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OpenCloudOS-Kernel/kernel/bpf/verifier.c

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bpf: verifier (add docs) this patch adds all of eBPF verfier documentation and empty bpf_check() The end goal for the verifier is to statically check safety of the program. Verifier will catch: - loops - out of range jumps - unreachable instructions - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention More details in Documentation/networking/filter.txt Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:02 +08:00
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
* Copyright (c) 2016 Facebook
bpf: verifier (add docs) this patch adds all of eBPF verfier documentation and empty bpf_check() The end goal for the verifier is to statically check safety of the program. Verifier will catch: - loops - out of range jumps - unreachable instructions - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention More details in Documentation/networking/filter.txt Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:02 +08:00
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*/
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <net/netlink.h>
#include <linux/file.h>
#include <linux/vmalloc.h>
/* bpf_check() is a static code analyzer that walks eBPF program
* instruction by instruction and updates register/stack state.
* All paths of conditional branches are analyzed until 'bpf_exit' insn.
*
* The first pass is depth-first-search to check that the program is a DAG.
* It rejects the following programs:
* - larger than BPF_MAXINSNS insns
* - if loop is present (detected via back-edge)
* - unreachable insns exist (shouldn't be a forest. program = one function)
* - out of bounds or malformed jumps
* The second pass is all possible path descent from the 1st insn.
* Since it's analyzing all pathes through the program, the length of the
* analysis is limited to 32k insn, which may be hit even if total number of
* insn is less then 4K, but there are too many branches that change stack/regs.
* Number of 'branches to be analyzed' is limited to 1k
*
* On entry to each instruction, each register has a type, and the instruction
* changes the types of the registers depending on instruction semantics.
* If instruction is BPF_MOV64_REG(BPF_REG_1, BPF_REG_5), then type of R5 is
* copied to R1.
*
* All registers are 64-bit.
* R0 - return register
* R1-R5 argument passing registers
* R6-R9 callee saved registers
* R10 - frame pointer read-only
*
* At the start of BPF program the register R1 contains a pointer to bpf_context
* and has type PTR_TO_CTX.
*
* Verifier tracks arithmetic operations on pointers in case:
* BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
* BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -20),
* 1st insn copies R10 (which has FRAME_PTR) type into R1
* and 2nd arithmetic instruction is pattern matched to recognize
* that it wants to construct a pointer to some element within stack.
* So after 2nd insn, the register R1 has type PTR_TO_STACK
* (and -20 constant is saved for further stack bounds checking).
* Meaning that this reg is a pointer to stack plus known immediate constant.
*
* Most of the time the registers have UNKNOWN_VALUE type, which
* means the register has some value, but it's not a valid pointer.
* (like pointer plus pointer becomes UNKNOWN_VALUE type)
*
* When verifier sees load or store instructions the type of base register
* can be: PTR_TO_MAP_VALUE, PTR_TO_CTX, FRAME_PTR. These are three pointer
* types recognized by check_mem_access() function.
*
* PTR_TO_MAP_VALUE means that this register is pointing to 'map element value'
* and the range of [ptr, ptr + map's value_size) is accessible.
*
* registers used to pass values to function calls are checked against
* function argument constraints.
*
* ARG_PTR_TO_MAP_KEY is one of such argument constraints.
* It means that the register type passed to this function must be
* PTR_TO_STACK and it will be used inside the function as
* 'pointer to map element key'
*
* For example the argument constraints for bpf_map_lookup_elem():
* .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
* .arg1_type = ARG_CONST_MAP_PTR,
* .arg2_type = ARG_PTR_TO_MAP_KEY,
*
* ret_type says that this function returns 'pointer to map elem value or null'
* function expects 1st argument to be a const pointer to 'struct bpf_map' and
* 2nd argument should be a pointer to stack, which will be used inside
* the helper function as a pointer to map element key.
*
* On the kernel side the helper function looks like:
* u64 bpf_map_lookup_elem(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
* {
* struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
* void *key = (void *) (unsigned long) r2;
* void *value;
*
* here kernel can access 'key' and 'map' pointers safely, knowing that
* [key, key + map->key_size) bytes are valid and were initialized on
* the stack of eBPF program.
* }
*
* Corresponding eBPF program may look like:
* BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), // after this insn R2 type is FRAME_PTR
* BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), // after this insn R2 type is PTR_TO_STACK
* BPF_LD_MAP_FD(BPF_REG_1, map_fd), // after this insn R1 type is CONST_PTR_TO_MAP
* BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
* here verifier looks at prototype of map_lookup_elem() and sees:
* .arg1_type == ARG_CONST_MAP_PTR and R1->type == CONST_PTR_TO_MAP, which is ok,
* Now verifier knows that this map has key of R1->map_ptr->key_size bytes
*
* Then .arg2_type == ARG_PTR_TO_MAP_KEY and R2->type == PTR_TO_STACK, ok so far,
* Now verifier checks that [R2, R2 + map's key_size) are within stack limits
* and were initialized prior to this call.
* If it's ok, then verifier allows this BPF_CALL insn and looks at
* .ret_type which is RET_PTR_TO_MAP_VALUE_OR_NULL, so it sets
* R0->type = PTR_TO_MAP_VALUE_OR_NULL which means bpf_map_lookup_elem() function
* returns ether pointer to map value or NULL.
*
* When type PTR_TO_MAP_VALUE_OR_NULL passes through 'if (reg != 0) goto +off'
* insn, the register holding that pointer in the true branch changes state to
* PTR_TO_MAP_VALUE and the same register changes state to CONST_IMM in the false
* branch. See check_cond_jmp_op().
*
* After the call R0 is set to return type of the function and registers R1-R5
* are set to NOT_INIT to indicate that they are no longer readable.
*/
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* types of values stored in eBPF registers */
enum bpf_reg_type {
NOT_INIT = 0, /* nothing was written into register */
UNKNOWN_VALUE, /* reg doesn't contain a valid pointer */
PTR_TO_CTX, /* reg points to bpf_context */
CONST_PTR_TO_MAP, /* reg points to struct bpf_map */
PTR_TO_MAP_VALUE, /* reg points to map element value */
PTR_TO_MAP_VALUE_OR_NULL,/* points to map elem value or NULL */
FRAME_PTR, /* reg == frame_pointer */
PTR_TO_STACK, /* reg == frame_pointer + imm */
CONST_IMM, /* constant integer value */
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
/* PTR_TO_PACKET represents:
* skb->data
* skb->data + imm
* skb->data + (u16) var
* skb->data + (u16) var + imm
* if (range > 0) then [ptr, ptr + range - off) is safe to access
* if (id > 0) means that some 'var' was added
* if (off > 0) menas that 'imm' was added
*/
PTR_TO_PACKET,
PTR_TO_PACKET_END, /* skb->data + headlen */
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
};
struct reg_state {
enum bpf_reg_type type;
union {
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
/* valid when type == CONST_IMM | PTR_TO_STACK | UNKNOWN_VALUE */
s64 imm;
/* valid when type == PTR_TO_PACKET* */
struct {
u32 id;
u16 off;
u16 range;
};
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
* PTR_TO_MAP_VALUE_OR_NULL
*/
struct bpf_map *map_ptr;
};
};
enum bpf_stack_slot_type {
STACK_INVALID, /* nothing was stored in this stack slot */
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
STACK_SPILL, /* register spilled into stack */
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
STACK_MISC /* BPF program wrote some data into this slot */
};
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
#define BPF_REG_SIZE 8 /* size of eBPF register in bytes */
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* state of the program:
* type of all registers and stack info
*/
struct verifier_state {
struct reg_state regs[MAX_BPF_REG];
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
u8 stack_slot_type[MAX_BPF_STACK];
struct reg_state spilled_regs[MAX_BPF_STACK / BPF_REG_SIZE];
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
};
/* linked list of verifier states used to prune search */
struct verifier_state_list {
struct verifier_state state;
struct verifier_state_list *next;
};
/* verifier_state + insn_idx are pushed to stack when branch is encountered */
struct verifier_stack_elem {
/* verifer state is 'st'
* before processing instruction 'insn_idx'
* and after processing instruction 'prev_insn_idx'
*/
struct verifier_state st;
int insn_idx;
int prev_insn_idx;
struct verifier_stack_elem *next;
};
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
/* single container for all structs
* one verifier_env per bpf_check() call
*/
struct verifier_env {
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
struct bpf_prog *prog; /* eBPF program being verified */
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
struct verifier_stack_elem *head; /* stack of verifier states to be processed */
int stack_size; /* number of states to be processed */
struct verifier_state cur_state; /* current verifier state */
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
struct verifier_state_list **explored_states; /* search pruning optimization */
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
u32 used_map_cnt; /* number of used maps */
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
bool allow_ptr_leaks;
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
};
bpf, verifier: further improve search pruning The verifier needs to go through every path of the program in order to check that it terminates safely, which can be quite a lot of instructions that need to be processed f.e. in cases with more branchy programs. With search pruning from f1bca824dabb ("bpf: add search pruning optimization to verifier") the search space can already be reduced significantly when the verifier detects that a previously walked path with same register and stack contents terminated already (see verifier's states_equal()), so the search can skip walking those states. When working with larger programs of > ~2000 (out of max 4096) insns, we found that the current limit of 32k instructions is easily hit. For example, a case we ran into is that the search space cannot be pruned due to branches at the beginning of the program that make use of certain stack space slots (STACK_MISC), which are never used in the remaining program (STACK_INVALID). Therefore, the verifier needs to walk paths for the slots in STACK_INVALID state, but also all remaining paths with a stack structure, where the slots are in STACK_MISC, which can nearly double the search space needed. After various experiments, we find that a limit of 64k processed insns is a more reasonable choice when dealing with larger programs in practice. This still allows to reject extreme crafted cases that can have a much higher complexity (f.e. > ~300k) within the 4096 insns limit due to search pruning not being able to take effect. Furthermore, we found that a lot of states can be pruned after a call instruction, f.e. we were able to reduce the search state by ~35% in some cases with this heuristic, trade-off is to keep a bit more states in env->explored_states. Usually, call instructions have a number of preceding register assignments and/or stack stores, where search pruning has a better chance to suceed in states_equal() test. The current code marks the branch targets with STATE_LIST_MARK in case of conditional jumps, and the next (t + 1) instruction in case of unconditional jump so that f.e. a backjump will walk it. We also did experiments with using t + insns[t].off + 1 as a marker in the unconditionally jump case instead of t + 1 with the rationale that these two branches of execution that converge after the label might have more potential of pruning. We found that it was a bit better, but not necessarily significantly better than the current state, perhaps also due to clang not generating back jumps often. Hence, we left that as is for now. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-06 04:33:17 +08:00
#define BPF_COMPLEXITY_LIMIT_INSNS 65536
#define BPF_COMPLEXITY_LIMIT_STACK 1024
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
struct bpf_call_arg_meta {
struct bpf_map *map_ptr;
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
bool raw_mode;
int regno;
int access_size;
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
};
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
/* verbose verifier prints what it's seeing
* bpf_check() is called under lock, so no race to access these global vars
*/
static u32 log_level, log_size, log_len;
static char *log_buf;
static DEFINE_MUTEX(bpf_verifier_lock);
/* log_level controls verbosity level of eBPF verifier.
* verbose() is used to dump the verification trace to the log, so the user
* can figure out what's wrong with the program
*/
bpf, verifier: annotate verbose printer with __printf The verbose() printer dumps the verifier state to user space, so let gcc take care to check calls to verbose() for (future) errors. make with W=1 correctly suggests: function might be possible candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-11-03 18:39:20 +08:00
static __printf(1, 2) void verbose(const char *fmt, ...)
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
{
va_list args;
if (log_level == 0 || log_len >= log_size - 1)
return;
va_start(args, fmt);
log_len += vscnprintf(log_buf + log_len, log_size - log_len, fmt, args);
va_end(args);
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* string representation of 'enum bpf_reg_type' */
static const char * const reg_type_str[] = {
[NOT_INIT] = "?",
[UNKNOWN_VALUE] = "inv",
[PTR_TO_CTX] = "ctx",
[CONST_PTR_TO_MAP] = "map_ptr",
[PTR_TO_MAP_VALUE] = "map_value",
[PTR_TO_MAP_VALUE_OR_NULL] = "map_value_or_null",
[FRAME_PTR] = "fp",
[PTR_TO_STACK] = "fp",
[CONST_IMM] = "imm",
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
[PTR_TO_PACKET] = "pkt",
[PTR_TO_PACKET_END] = "pkt_end",
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
};
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
static void print_verifier_state(struct verifier_state *state)
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
{
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
struct reg_state *reg;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
enum bpf_reg_type t;
int i;
for (i = 0; i < MAX_BPF_REG; i++) {
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
reg = &state->regs[i];
t = reg->type;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (t == NOT_INIT)
continue;
verbose(" R%d=%s", i, reg_type_str[t]);
if (t == CONST_IMM || t == PTR_TO_STACK)
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
verbose("%lld", reg->imm);
else if (t == PTR_TO_PACKET)
verbose("(id=%d,off=%d,r=%d)",
reg->id, reg->off, reg->range);
else if (t == UNKNOWN_VALUE && reg->imm)
verbose("%lld", reg->imm);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
else if (t == CONST_PTR_TO_MAP || t == PTR_TO_MAP_VALUE ||
t == PTR_TO_MAP_VALUE_OR_NULL)
verbose("(ks=%d,vs=%d)",
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
reg->map_ptr->key_size,
reg->map_ptr->value_size);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
}
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
if (state->stack_slot_type[i] == STACK_SPILL)
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose(" fp%d=%s", -MAX_BPF_STACK + i,
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
reg_type_str[state->spilled_regs[i / BPF_REG_SIZE].type]);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
}
verbose("\n");
}
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
static const char *const bpf_class_string[] = {
[BPF_LD] = "ld",
[BPF_LDX] = "ldx",
[BPF_ST] = "st",
[BPF_STX] = "stx",
[BPF_ALU] = "alu",
[BPF_JMP] = "jmp",
[BPF_RET] = "BUG",
[BPF_ALU64] = "alu64",
};
bpf: fix out of bounds access in verifier log when the verifier log is enabled the print_bpf_insn() is doing bpf_alu_string[BPF_OP(insn->code) >> 4] and bpf_jmp_string[BPF_OP(insn->code) >> 4] where BPF_OP is a 4-bit instruction opcode. Malformed insns can cause out of bounds access. Fix it by sizing arrays appropriately. The bug was found by clang address sanitizer with libfuzzer. Reported-by: Yonghong Song <yhs@plumgrid.com> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-09-09 04:40:01 +08:00
static const char *const bpf_alu_string[16] = {
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
[BPF_ADD >> 4] = "+=",
[BPF_SUB >> 4] = "-=",
[BPF_MUL >> 4] = "*=",
[BPF_DIV >> 4] = "/=",
[BPF_OR >> 4] = "|=",
[BPF_AND >> 4] = "&=",
[BPF_LSH >> 4] = "<<=",
[BPF_RSH >> 4] = ">>=",
[BPF_NEG >> 4] = "neg",
[BPF_MOD >> 4] = "%=",
[BPF_XOR >> 4] = "^=",
[BPF_MOV >> 4] = "=",
[BPF_ARSH >> 4] = "s>>=",
[BPF_END >> 4] = "endian",
};
static const char *const bpf_ldst_string[] = {
[BPF_W >> 3] = "u32",
[BPF_H >> 3] = "u16",
[BPF_B >> 3] = "u8",
[BPF_DW >> 3] = "u64",
};
bpf: fix out of bounds access in verifier log when the verifier log is enabled the print_bpf_insn() is doing bpf_alu_string[BPF_OP(insn->code) >> 4] and bpf_jmp_string[BPF_OP(insn->code) >> 4] where BPF_OP is a 4-bit instruction opcode. Malformed insns can cause out of bounds access. Fix it by sizing arrays appropriately. The bug was found by clang address sanitizer with libfuzzer. Reported-by: Yonghong Song <yhs@plumgrid.com> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-09-09 04:40:01 +08:00
static const char *const bpf_jmp_string[16] = {
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
[BPF_JA >> 4] = "jmp",
[BPF_JEQ >> 4] = "==",
[BPF_JGT >> 4] = ">",
[BPF_JGE >> 4] = ">=",
[BPF_JSET >> 4] = "&",
[BPF_JNE >> 4] = "!=",
[BPF_JSGT >> 4] = "s>",
[BPF_JSGE >> 4] = "s>=",
[BPF_CALL >> 4] = "call",
[BPF_EXIT >> 4] = "exit",
};
static void print_bpf_insn(struct bpf_insn *insn)
{
u8 class = BPF_CLASS(insn->code);
if (class == BPF_ALU || class == BPF_ALU64) {
if (BPF_SRC(insn->code) == BPF_X)
verbose("(%02x) %sr%d %s %sr%d\n",
insn->code, class == BPF_ALU ? "(u32) " : "",
insn->dst_reg,
bpf_alu_string[BPF_OP(insn->code) >> 4],
class == BPF_ALU ? "(u32) " : "",
insn->src_reg);
else
verbose("(%02x) %sr%d %s %s%d\n",
insn->code, class == BPF_ALU ? "(u32) " : "",
insn->dst_reg,
bpf_alu_string[BPF_OP(insn->code) >> 4],
class == BPF_ALU ? "(u32) " : "",
insn->imm);
} else if (class == BPF_STX) {
if (BPF_MODE(insn->code) == BPF_MEM)
verbose("(%02x) *(%s *)(r%d %+d) = r%d\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->dst_reg,
insn->off, insn->src_reg);
else if (BPF_MODE(insn->code) == BPF_XADD)
verbose("(%02x) lock *(%s *)(r%d %+d) += r%d\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->dst_reg, insn->off,
insn->src_reg);
else
verbose("BUG_%02x\n", insn->code);
} else if (class == BPF_ST) {
if (BPF_MODE(insn->code) != BPF_MEM) {
verbose("BUG_st_%02x\n", insn->code);
return;
}
verbose("(%02x) *(%s *)(r%d %+d) = %d\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->dst_reg,
insn->off, insn->imm);
} else if (class == BPF_LDX) {
if (BPF_MODE(insn->code) != BPF_MEM) {
verbose("BUG_ldx_%02x\n", insn->code);
return;
}
verbose("(%02x) r%d = *(%s *)(r%d %+d)\n",
insn->code, insn->dst_reg,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->src_reg, insn->off);
} else if (class == BPF_LD) {
if (BPF_MODE(insn->code) == BPF_ABS) {
verbose("(%02x) r0 = *(%s *)skb[%d]\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->imm);
} else if (BPF_MODE(insn->code) == BPF_IND) {
verbose("(%02x) r0 = *(%s *)skb[r%d + %d]\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->src_reg, insn->imm);
} else if (BPF_MODE(insn->code) == BPF_IMM) {
verbose("(%02x) r%d = 0x%x\n",
insn->code, insn->dst_reg, insn->imm);
} else {
verbose("BUG_ld_%02x\n", insn->code);
return;
}
} else if (class == BPF_JMP) {
u8 opcode = BPF_OP(insn->code);
if (opcode == BPF_CALL) {
verbose("(%02x) call %d\n", insn->code, insn->imm);
} else if (insn->code == (BPF_JMP | BPF_JA)) {
verbose("(%02x) goto pc%+d\n",
insn->code, insn->off);
} else if (insn->code == (BPF_JMP | BPF_EXIT)) {
verbose("(%02x) exit\n", insn->code);
} else if (BPF_SRC(insn->code) == BPF_X) {
verbose("(%02x) if r%d %s r%d goto pc%+d\n",
insn->code, insn->dst_reg,
bpf_jmp_string[BPF_OP(insn->code) >> 4],
insn->src_reg, insn->off);
} else {
verbose("(%02x) if r%d %s 0x%x goto pc%+d\n",
insn->code, insn->dst_reg,
bpf_jmp_string[BPF_OP(insn->code) >> 4],
insn->imm, insn->off);
}
} else {
verbose("(%02x) %s\n", insn->code, bpf_class_string[class]);
}
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
static int pop_stack(struct verifier_env *env, int *prev_insn_idx)
{
struct verifier_stack_elem *elem;
int insn_idx;
if (env->head == NULL)
return -1;
memcpy(&env->cur_state, &env->head->st, sizeof(env->cur_state));
insn_idx = env->head->insn_idx;
if (prev_insn_idx)
*prev_insn_idx = env->head->prev_insn_idx;
elem = env->head->next;
kfree(env->head);
env->head = elem;
env->stack_size--;
return insn_idx;
}
static struct verifier_state *push_stack(struct verifier_env *env, int insn_idx,
int prev_insn_idx)
{
struct verifier_stack_elem *elem;
elem = kmalloc(sizeof(struct verifier_stack_elem), GFP_KERNEL);
if (!elem)
goto err;
memcpy(&elem->st, &env->cur_state, sizeof(env->cur_state));
elem->insn_idx = insn_idx;
elem->prev_insn_idx = prev_insn_idx;
elem->next = env->head;
env->head = elem;
env->stack_size++;
bpf, verifier: further improve search pruning The verifier needs to go through every path of the program in order to check that it terminates safely, which can be quite a lot of instructions that need to be processed f.e. in cases with more branchy programs. With search pruning from f1bca824dabb ("bpf: add search pruning optimization to verifier") the search space can already be reduced significantly when the verifier detects that a previously walked path with same register and stack contents terminated already (see verifier's states_equal()), so the search can skip walking those states. When working with larger programs of > ~2000 (out of max 4096) insns, we found that the current limit of 32k instructions is easily hit. For example, a case we ran into is that the search space cannot be pruned due to branches at the beginning of the program that make use of certain stack space slots (STACK_MISC), which are never used in the remaining program (STACK_INVALID). Therefore, the verifier needs to walk paths for the slots in STACK_INVALID state, but also all remaining paths with a stack structure, where the slots are in STACK_MISC, which can nearly double the search space needed. After various experiments, we find that a limit of 64k processed insns is a more reasonable choice when dealing with larger programs in practice. This still allows to reject extreme crafted cases that can have a much higher complexity (f.e. > ~300k) within the 4096 insns limit due to search pruning not being able to take effect. Furthermore, we found that a lot of states can be pruned after a call instruction, f.e. we were able to reduce the search state by ~35% in some cases with this heuristic, trade-off is to keep a bit more states in env->explored_states. Usually, call instructions have a number of preceding register assignments and/or stack stores, where search pruning has a better chance to suceed in states_equal() test. The current code marks the branch targets with STATE_LIST_MARK in case of conditional jumps, and the next (t + 1) instruction in case of unconditional jump so that f.e. a backjump will walk it. We also did experiments with using t + insns[t].off + 1 as a marker in the unconditionally jump case instead of t + 1 with the rationale that these two branches of execution that converge after the label might have more potential of pruning. We found that it was a bit better, but not necessarily significantly better than the current state, perhaps also due to clang not generating back jumps often. Hence, we left that as is for now. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-06 04:33:17 +08:00
if (env->stack_size > BPF_COMPLEXITY_LIMIT_STACK) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("BPF program is too complex\n");
goto err;
}
return &elem->st;
err:
/* pop all elements and return */
while (pop_stack(env, NULL) >= 0);
return NULL;
}
#define CALLER_SAVED_REGS 6
static const int caller_saved[CALLER_SAVED_REGS] = {
BPF_REG_0, BPF_REG_1, BPF_REG_2, BPF_REG_3, BPF_REG_4, BPF_REG_5
};
static void init_reg_state(struct reg_state *regs)
{
int i;
for (i = 0; i < MAX_BPF_REG; i++) {
regs[i].type = NOT_INIT;
regs[i].imm = 0;
}
/* frame pointer */
regs[BPF_REG_FP].type = FRAME_PTR;
/* 1st arg to a function */
regs[BPF_REG_1].type = PTR_TO_CTX;
}
static void mark_reg_unknown_value(struct reg_state *regs, u32 regno)
{
BUG_ON(regno >= MAX_BPF_REG);
regs[regno].type = UNKNOWN_VALUE;
regs[regno].imm = 0;
}
enum reg_arg_type {
SRC_OP, /* register is used as source operand */
DST_OP, /* register is used as destination operand */
DST_OP_NO_MARK /* same as above, check only, don't mark */
};
static int check_reg_arg(struct reg_state *regs, u32 regno,
enum reg_arg_type t)
{
if (regno >= MAX_BPF_REG) {
verbose("R%d is invalid\n", regno);
return -EINVAL;
}
if (t == SRC_OP) {
/* check whether register used as source operand can be read */
if (regs[regno].type == NOT_INIT) {
verbose("R%d !read_ok\n", regno);
return -EACCES;
}
} else {
/* check whether register used as dest operand can be written to */
if (regno == BPF_REG_FP) {
verbose("frame pointer is read only\n");
return -EACCES;
}
if (t == DST_OP)
mark_reg_unknown_value(regs, regno);
}
return 0;
}
static int bpf_size_to_bytes(int bpf_size)
{
if (bpf_size == BPF_W)
return 4;
else if (bpf_size == BPF_H)
return 2;
else if (bpf_size == BPF_B)
return 1;
else if (bpf_size == BPF_DW)
return 8;
else
return -EINVAL;
}
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
static bool is_spillable_regtype(enum bpf_reg_type type)
{
switch (type) {
case PTR_TO_MAP_VALUE:
case PTR_TO_MAP_VALUE_OR_NULL:
case PTR_TO_STACK:
case PTR_TO_CTX:
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
case PTR_TO_PACKET:
case PTR_TO_PACKET_END:
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
case FRAME_PTR:
case CONST_PTR_TO_MAP:
return true;
default:
return false;
}
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* check_stack_read/write functions track spill/fill of registers,
* stack boundary and alignment are checked in check_mem_access()
*/
static int check_stack_write(struct verifier_state *state, int off, int size,
int value_regno)
{
int i;
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
/* caller checked that off % size == 0 and -MAX_BPF_STACK <= off < 0,
* so it's aligned access and [off, off + size) are within stack limits
*/
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (value_regno >= 0 &&
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
is_spillable_regtype(state->regs[value_regno].type)) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* register containing pointer is being spilled into stack */
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
if (size != BPF_REG_SIZE) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("invalid size of register spill\n");
return -EACCES;
}
/* save register state */
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE] =
state->regs[value_regno];
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
for (i = 0; i < BPF_REG_SIZE; i++)
state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_SPILL;
} else {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* regular write of data into stack */
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE] =
(struct reg_state) {};
for (i = 0; i < size; i++)
state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_MISC;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
}
return 0;
}
static int check_stack_read(struct verifier_state *state, int off, int size,
int value_regno)
{
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
u8 *slot_type;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
int i;
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
slot_type = &state->stack_slot_type[MAX_BPF_STACK + off];
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
if (slot_type[0] == STACK_SPILL) {
if (size != BPF_REG_SIZE) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("invalid size of register spill\n");
return -EACCES;
}
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
for (i = 1; i < BPF_REG_SIZE; i++) {
if (slot_type[i] != STACK_SPILL) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("corrupted spill memory\n");
return -EACCES;
}
}
if (value_regno >= 0)
/* restore register state from stack */
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
state->regs[value_regno] =
state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE];
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return 0;
} else {
for (i = 0; i < size; i++) {
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
if (slot_type[i] != STACK_MISC) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("invalid read from stack off %d+%d size %d\n",
off, i, size);
return -EACCES;
}
}
if (value_regno >= 0)
/* have read misc data from the stack */
mark_reg_unknown_value(state->regs, value_regno);
return 0;
}
}
/* check read/write into map element returned by bpf_map_lookup_elem() */
static int check_map_access(struct verifier_env *env, u32 regno, int off,
int size)
{
struct bpf_map *map = env->cur_state.regs[regno].map_ptr;
if (off < 0 || off + size > map->value_size) {
verbose("invalid access to map value, value_size=%d off=%d size=%d\n",
map->value_size, off, size);
return -EACCES;
}
return 0;
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
#define MAX_PACKET_OFF 0xffff
static int check_packet_access(struct verifier_env *env, u32 regno, int off,
int size)
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *reg = &regs[regno];
bpf: support decreasing order in direct packet access when packet headers are accessed in 'decreasing' order (like TCP port may be fetched before the program reads IP src) the llvm may generate the following code: [...] // R7=pkt(id=0,off=22,r=70) r2 = *(u32 *)(r7 +0) // good access [...] r7 += 40 // R7=pkt(id=0,off=62,r=70) r8 = *(u32 *)(r7 +0) // good access [...] r1 = *(u32 *)(r7 -20) // this one will fail though it's within a safe range // it's doing *(u32*)(skb->data + 42) Fix verifier to recognize such code pattern Alos turned out that 'off > range' condition is not a verifier bug. It's a buggy program that may do something like: if (ptr + 50 > data_end) return 0; ptr += 60; *(u32*)ptr; in such case emit "invalid access to packet, off=0 size=4, R1(id=0,off=60,r=50)" error message, so all information is available for the program author to fix the program. Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-20 09:17:13 +08:00
off += reg->off;
if (off < 0 || off + size > reg->range) {
verbose("invalid access to packet, off=%d size=%d, R%d(id=%d,off=%d,r=%d)\n",
off, size, regno, reg->id, reg->off, reg->range);
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
return -EACCES;
}
return 0;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* check access to 'struct bpf_context' fields */
static int check_ctx_access(struct verifier_env *env, int off, int size,
enum bpf_access_type t)
{
if (env->prog->aux->ops->is_valid_access &&
bpf: sanitize bpf tracepoint access during bpf program loading remember the last byte of ctx access and at the time of attaching the program to tracepoint check that the program doesn't access bytes beyond defined in tracepoint fields This also disallows access to __dynamic_array fields, but can be relaxed in the future. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-07 09:43:28 +08:00
env->prog->aux->ops->is_valid_access(off, size, t)) {
/* remember the offset of last byte accessed in ctx */
if (env->prog->aux->max_ctx_offset < off + size)
env->prog->aux->max_ctx_offset = off + size;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return 0;
bpf: sanitize bpf tracepoint access during bpf program loading remember the last byte of ctx access and at the time of attaching the program to tracepoint check that the program doesn't access bytes beyond defined in tracepoint fields This also disallows access to __dynamic_array fields, but can be relaxed in the future. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-07 09:43:28 +08:00
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("invalid bpf_context access off=%d size=%d\n", off, size);
return -EACCES;
}
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
static bool is_pointer_value(struct verifier_env *env, int regno)
{
if (env->allow_ptr_leaks)
return false;
switch (env->cur_state.regs[regno].type) {
case UNKNOWN_VALUE:
case CONST_IMM:
return false;
default:
return true;
}
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
static int check_ptr_alignment(struct verifier_env *env, struct reg_state *reg,
int off, int size)
{
if (reg->type != PTR_TO_PACKET) {
if (off % size != 0) {
verbose("misaligned access off %d size %d\n", off, size);
return -EACCES;
} else {
return 0;
}
}
switch (env->prog->type) {
case BPF_PROG_TYPE_SCHED_CLS:
case BPF_PROG_TYPE_SCHED_ACT:
break;
default:
verbose("verifier is misconfigured\n");
return -EACCES;
}
if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
/* misaligned access to packet is ok on x86,arm,arm64 */
return 0;
if (reg->id && size != 1) {
verbose("Unknown packet alignment. Only byte-sized access allowed\n");
return -EACCES;
}
/* skb->data is NET_IP_ALIGN-ed */
if ((NET_IP_ALIGN + reg->off + off) % size != 0) {
verbose("misaligned packet access off %d+%d+%d size %d\n",
NET_IP_ALIGN, reg->off, off, size);
return -EACCES;
}
return 0;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* check whether memory at (regno + off) is accessible for t = (read | write)
* if t==write, value_regno is a register which value is stored into memory
* if t==read, value_regno is a register which will receive the value from memory
* if t==write && value_regno==-1, some unknown value is stored into memory
* if t==read && value_regno==-1, don't care what we read from memory
*/
static int check_mem_access(struct verifier_env *env, u32 regno, int off,
int bpf_size, enum bpf_access_type t,
int value_regno)
{
struct verifier_state *state = &env->cur_state;
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
struct reg_state *reg = &state->regs[regno];
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
int size, err = 0;
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
if (reg->type == PTR_TO_STACK)
off += reg->imm;
ebpf: Allow dereferences of PTR_TO_STACK registers mov %rsp, %r1 ; r1 = rsp add $-8, %r1 ; r1 = rsp - 8 store_q $123, -8(%rsp) ; *(u64*)r1 = 123 <- valid store_q $123, (%r1) ; *(u64*)r1 = 123 <- previously invalid mov $0, %r0 exit ; Always need to exit And we'd get the following error: 0: (bf) r1 = r10 1: (07) r1 += -8 2: (7a) *(u64 *)(r10 -8) = 999 3: (7a) *(u64 *)(r1 +0) = 999 R1 invalid mem access 'fp' Unable to load program We already know that a register is a stack address and the appropriate offset, so we should be able to validate those references as well. Signed-off-by: Alex Gartrell <agartrell@fb.com> Acked-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-07-24 05:24:40 +08:00
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
size = bpf_size_to_bytes(bpf_size);
if (size < 0)
return size;
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
err = check_ptr_alignment(env, reg, off, size);
if (err)
return err;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
if (reg->type == PTR_TO_MAP_VALUE) {
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
if (t == BPF_WRITE && value_regno >= 0 &&
is_pointer_value(env, value_regno)) {
verbose("R%d leaks addr into map\n", value_regno);
return -EACCES;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
err = check_map_access(env, regno, off, size);
if (!err && t == BPF_READ && value_regno >= 0)
mark_reg_unknown_value(state->regs, value_regno);
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
} else if (reg->type == PTR_TO_CTX) {
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
if (t == BPF_WRITE && value_regno >= 0 &&
is_pointer_value(env, value_regno)) {
verbose("R%d leaks addr into ctx\n", value_regno);
return -EACCES;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
err = check_ctx_access(env, off, size, t);
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
if (!err && t == BPF_READ && value_regno >= 0) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
mark_reg_unknown_value(state->regs, value_regno);
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
if (off == offsetof(struct __sk_buff, data) &&
env->allow_ptr_leaks)
/* note that reg.[id|off|range] == 0 */
state->regs[value_regno].type = PTR_TO_PACKET;
else if (off == offsetof(struct __sk_buff, data_end) &&
env->allow_ptr_leaks)
state->regs[value_regno].type = PTR_TO_PACKET_END;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
} else if (reg->type == FRAME_PTR || reg->type == PTR_TO_STACK) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (off >= 0 || off < -MAX_BPF_STACK) {
verbose("invalid stack off=%d size=%d\n", off, size);
return -EACCES;
}
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
if (t == BPF_WRITE) {
if (!env->allow_ptr_leaks &&
state->stack_slot_type[MAX_BPF_STACK + off] == STACK_SPILL &&
size != BPF_REG_SIZE) {
verbose("attempt to corrupt spilled pointer on stack\n");
return -EACCES;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
err = check_stack_write(state, off, size, value_regno);
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
} else {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
err = check_stack_read(state, off, size, value_regno);
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
} else if (state->regs[regno].type == PTR_TO_PACKET) {
if (t == BPF_WRITE) {
verbose("cannot write into packet\n");
return -EACCES;
}
err = check_packet_access(env, regno, off, size);
if (!err && t == BPF_READ && value_regno >= 0)
mark_reg_unknown_value(state->regs, value_regno);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else {
verbose("R%d invalid mem access '%s'\n",
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
regno, reg_type_str[reg->type]);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return -EACCES;
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
if (!err && size <= 2 && value_regno >= 0 && env->allow_ptr_leaks &&
state->regs[value_regno].type == UNKNOWN_VALUE) {
/* 1 or 2 byte load zero-extends, determine the number of
* zero upper bits. Not doing it fo 4 byte load, since
* such values cannot be added to ptr_to_packet anyway.
*/
state->regs[value_regno].imm = 64 - size * 8;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return err;
}
static int check_xadd(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
int err;
if ((BPF_SIZE(insn->code) != BPF_W && BPF_SIZE(insn->code) != BPF_DW) ||
insn->imm != 0) {
verbose("BPF_XADD uses reserved fields\n");
return -EINVAL;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
/* check src2 operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
/* check whether atomic_add can read the memory */
err = check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_READ, -1);
if (err)
return err;
/* check whether atomic_add can write into the same memory */
return check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE, -1);
}
/* when register 'regno' is passed into function that will read 'access_size'
* bytes from that pointer, make sure that it's within stack boundary
* and all elements of stack are initialized
*/
bpf: add new arg_type that allows for 0 sized stack buffer Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-02-20 06:05:22 +08:00
static int check_stack_boundary(struct verifier_env *env, int regno,
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
int access_size, bool zero_size_allowed,
struct bpf_call_arg_meta *meta)
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
{
struct verifier_state *state = &env->cur_state;
struct reg_state *regs = state->regs;
int off, i;
bpf: add new arg_type that allows for 0 sized stack buffer Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-02-20 06:05:22 +08:00
if (regs[regno].type != PTR_TO_STACK) {
if (zero_size_allowed && access_size == 0 &&
regs[regno].type == CONST_IMM &&
regs[regno].imm == 0)
return 0;
verbose("R%d type=%s expected=%s\n", regno,
reg_type_str[regs[regno].type],
reg_type_str[PTR_TO_STACK]);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return -EACCES;
bpf: add new arg_type that allows for 0 sized stack buffer Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-02-20 06:05:22 +08:00
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
off = regs[regno].imm;
if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
access_size <= 0) {
verbose("invalid stack type R%d off=%d access_size=%d\n",
regno, off, access_size);
return -EACCES;
}
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
if (meta && meta->raw_mode) {
meta->access_size = access_size;
meta->regno = regno;
return 0;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
for (i = 0; i < access_size; i++) {
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
if (state->stack_slot_type[MAX_BPF_STACK + off + i] != STACK_MISC) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("invalid indirect read from stack off %d+%d size %d\n",
off, i, access_size);
return -EACCES;
}
}
return 0;
}
static int check_func_arg(struct verifier_env *env, u32 regno,
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
enum bpf_arg_type arg_type,
struct bpf_call_arg_meta *meta)
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
{
struct reg_state *reg = env->cur_state.regs + regno;
enum bpf_reg_type expected_type;
int err = 0;
ebpf: verifier: check that call reg with ARG_ANYTHING is initialized I noticed that a helper function with argument type ARG_ANYTHING does not need to have an initialized value (register). This can worst case lead to unintented stack memory leakage in future helper functions if they are not carefully designed, or unintended application behaviour in case the application developer was not careful enough to match a correct helper function signature in the API. The underlying issue is that ARG_ANYTHING should actually be split into two different semantics: 1) ARG_DONTCARE for function arguments that the helper function does not care about (in other words: the default for unused function arguments), and 2) ARG_ANYTHING that is an argument actually being used by a helper function and *guaranteed* to be an initialized register. The current risk is low: ARG_ANYTHING is only used for the 'flags' argument (r4) in bpf_map_update_elem() that internally does strict checking. Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-13 00:21:42 +08:00
if (arg_type == ARG_DONTCARE)
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return 0;
if (reg->type == NOT_INIT) {
verbose("R%d !read_ok\n", regno);
return -EACCES;
}
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
if (arg_type == ARG_ANYTHING) {
if (is_pointer_value(env, regno)) {
verbose("R%d leaks addr into helper function\n", regno);
return -EACCES;
}
ebpf: verifier: check that call reg with ARG_ANYTHING is initialized I noticed that a helper function with argument type ARG_ANYTHING does not need to have an initialized value (register). This can worst case lead to unintented stack memory leakage in future helper functions if they are not carefully designed, or unintended application behaviour in case the application developer was not careful enough to match a correct helper function signature in the API. The underlying issue is that ARG_ANYTHING should actually be split into two different semantics: 1) ARG_DONTCARE for function arguments that the helper function does not care about (in other words: the default for unused function arguments), and 2) ARG_ANYTHING that is an argument actually being used by a helper function and *guaranteed* to be an initialized register. The current risk is low: ARG_ANYTHING is only used for the 'flags' argument (r4) in bpf_map_update_elem() that internally does strict checking. Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-13 00:21:42 +08:00
return 0;
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
}
ebpf: verifier: check that call reg with ARG_ANYTHING is initialized I noticed that a helper function with argument type ARG_ANYTHING does not need to have an initialized value (register). This can worst case lead to unintented stack memory leakage in future helper functions if they are not carefully designed, or unintended application behaviour in case the application developer was not careful enough to match a correct helper function signature in the API. The underlying issue is that ARG_ANYTHING should actually be split into two different semantics: 1) ARG_DONTCARE for function arguments that the helper function does not care about (in other words: the default for unused function arguments), and 2) ARG_ANYTHING that is an argument actually being used by a helper function and *guaranteed* to be an initialized register. The current risk is low: ARG_ANYTHING is only used for the 'flags' argument (r4) in bpf_map_update_elem() that internally does strict checking. Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-13 00:21:42 +08:00
bpf: add new arg_type that allows for 0 sized stack buffer Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-02-20 06:05:22 +08:00
if (arg_type == ARG_PTR_TO_MAP_KEY ||
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
arg_type == ARG_PTR_TO_MAP_VALUE) {
expected_type = PTR_TO_STACK;
bpf: add new arg_type that allows for 0 sized stack buffer Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-02-20 06:05:22 +08:00
} else if (arg_type == ARG_CONST_STACK_SIZE ||
arg_type == ARG_CONST_STACK_SIZE_OR_ZERO) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
expected_type = CONST_IMM;
} else if (arg_type == ARG_CONST_MAP_PTR) {
expected_type = CONST_PTR_TO_MAP;
tc: bpf: generalize pedit action existing TC action 'pedit' can munge any bits of the packet. Generalize it for use in bpf programs attached as cls_bpf and act_bpf via bpf_skb_store_bytes() helper function. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Jiri Pirko <jiri@resnulli.us> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-27 10:53:57 +08:00
} else if (arg_type == ARG_PTR_TO_CTX) {
expected_type = PTR_TO_CTX;
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
} else if (arg_type == ARG_PTR_TO_STACK ||
arg_type == ARG_PTR_TO_RAW_STACK) {
bpf: add new arg_type that allows for 0 sized stack buffer Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-02-20 06:05:22 +08:00
expected_type = PTR_TO_STACK;
/* One exception here. In case function allows for NULL to be
* passed in as argument, it's a CONST_IMM type. Final test
* happens during stack boundary checking.
*/
if (reg->type == CONST_IMM && reg->imm == 0)
expected_type = CONST_IMM;
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
meta->raw_mode = arg_type == ARG_PTR_TO_RAW_STACK;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else {
verbose("unsupported arg_type %d\n", arg_type);
return -EFAULT;
}
if (reg->type != expected_type) {
verbose("R%d type=%s expected=%s\n", regno,
reg_type_str[reg->type], reg_type_str[expected_type]);
return -EACCES;
}
if (arg_type == ARG_CONST_MAP_PTR) {
/* bpf_map_xxx(map_ptr) call: remember that map_ptr */
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
meta->map_ptr = reg->map_ptr;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else if (arg_type == ARG_PTR_TO_MAP_KEY) {
/* bpf_map_xxx(..., map_ptr, ..., key) call:
* check that [key, key + map->key_size) are within
* stack limits and initialized
*/
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
if (!meta->map_ptr) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* in function declaration map_ptr must come before
* map_key, so that it's verified and known before
* we have to check map_key here. Otherwise it means
* that kernel subsystem misconfigured verifier
*/
verbose("invalid map_ptr to access map->key\n");
return -EACCES;
}
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
err = check_stack_boundary(env, regno, meta->map_ptr->key_size,
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
false, NULL);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else if (arg_type == ARG_PTR_TO_MAP_VALUE) {
/* bpf_map_xxx(..., map_ptr, ..., value) call:
* check [value, value + map->value_size) validity
*/
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
if (!meta->map_ptr) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* kernel subsystem misconfigured verifier */
verbose("invalid map_ptr to access map->value\n");
return -EACCES;
}
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
err = check_stack_boundary(env, regno,
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
meta->map_ptr->value_size,
false, NULL);
bpf: add new arg_type that allows for 0 sized stack buffer Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-02-20 06:05:22 +08:00
} else if (arg_type == ARG_CONST_STACK_SIZE ||
arg_type == ARG_CONST_STACK_SIZE_OR_ZERO) {
bool zero_size_allowed = (arg_type == ARG_CONST_STACK_SIZE_OR_ZERO);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* bpf_xxx(..., buf, len) call will access 'len' bytes
* from stack pointer 'buf'. Check it
* note: regno == len, regno - 1 == buf
*/
if (regno == 0) {
/* kernel subsystem misconfigured verifier */
verbose("ARG_CONST_STACK_SIZE cannot be first argument\n");
return -EACCES;
}
bpf: add new arg_type that allows for 0 sized stack buffer Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-02-20 06:05:22 +08:00
err = check_stack_boundary(env, regno - 1, reg->imm,
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
zero_size_allowed, meta);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
}
return err;
}
bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter According to the perf_event_map_fd and index, the function bpf_perf_event_read() can convert the corresponding map value to the pointer to struct perf_event and return the Hardware PMU counter value. Signed-off-by: Kaixu Xia <xiakaixu@huawei.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-08-06 15:02:35 +08:00
static int check_map_func_compatibility(struct bpf_map *map, int func_id)
{
if (!map)
return 0;
bpf: fix check_map_func_compatibility logic The commit 35578d798400 ("bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter") introduced clever way to check bpf_helper<->map_type compatibility. Later on commit a43eec304259 ("bpf: introduce bpf_perf_event_output() helper") adjusted the logic and inadvertently broke it. Get rid of the clever bool compare and go back to two-way check from map and from helper perspective. Fixes: a43eec304259 ("bpf: introduce bpf_perf_event_output() helper") Reported-by: Jann Horn <jannh@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-28 09:56:21 +08:00
/* We need a two way check, first is from map perspective ... */
switch (map->map_type) {
case BPF_MAP_TYPE_PROG_ARRAY:
if (func_id != BPF_FUNC_tail_call)
goto error;
break;
case BPF_MAP_TYPE_PERF_EVENT_ARRAY:
if (func_id != BPF_FUNC_perf_event_read &&
func_id != BPF_FUNC_perf_event_output)
goto error;
break;
case BPF_MAP_TYPE_STACK_TRACE:
if (func_id != BPF_FUNC_get_stackid)
goto error;
break;
default:
break;
}
/* ... and second from the function itself. */
switch (func_id) {
case BPF_FUNC_tail_call:
if (map->map_type != BPF_MAP_TYPE_PROG_ARRAY)
goto error;
break;
case BPF_FUNC_perf_event_read:
case BPF_FUNC_perf_event_output:
if (map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
goto error;
break;
case BPF_FUNC_get_stackid:
if (map->map_type != BPF_MAP_TYPE_STACK_TRACE)
goto error;
break;
default:
break;
bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter According to the perf_event_map_fd and index, the function bpf_perf_event_read() can convert the corresponding map value to the pointer to struct perf_event and return the Hardware PMU counter value. Signed-off-by: Kaixu Xia <xiakaixu@huawei.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-08-06 15:02:35 +08:00
}
return 0;
bpf: fix check_map_func_compatibility logic The commit 35578d798400 ("bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter") introduced clever way to check bpf_helper<->map_type compatibility. Later on commit a43eec304259 ("bpf: introduce bpf_perf_event_output() helper") adjusted the logic and inadvertently broke it. Get rid of the clever bool compare and go back to two-way check from map and from helper perspective. Fixes: a43eec304259 ("bpf: introduce bpf_perf_event_output() helper") Reported-by: Jann Horn <jannh@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-28 09:56:21 +08:00
error:
verbose("cannot pass map_type %d into func %d\n",
map->map_type, func_id);
return -EINVAL;
bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter According to the perf_event_map_fd and index, the function bpf_perf_event_read() can convert the corresponding map value to the pointer to struct perf_event and return the Hardware PMU counter value. Signed-off-by: Kaixu Xia <xiakaixu@huawei.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-08-06 15:02:35 +08:00
}
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
static int check_raw_mode(const struct bpf_func_proto *fn)
{
int count = 0;
if (fn->arg1_type == ARG_PTR_TO_RAW_STACK)
count++;
if (fn->arg2_type == ARG_PTR_TO_RAW_STACK)
count++;
if (fn->arg3_type == ARG_PTR_TO_RAW_STACK)
count++;
if (fn->arg4_type == ARG_PTR_TO_RAW_STACK)
count++;
if (fn->arg5_type == ARG_PTR_TO_RAW_STACK)
count++;
return count > 1 ? -EINVAL : 0;
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
static void clear_all_pkt_pointers(struct verifier_env *env)
{
struct verifier_state *state = &env->cur_state;
struct reg_state *regs = state->regs, *reg;
int i;
for (i = 0; i < MAX_BPF_REG; i++)
if (regs[i].type == PTR_TO_PACKET ||
regs[i].type == PTR_TO_PACKET_END)
mark_reg_unknown_value(regs, i);
for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
if (state->stack_slot_type[i] != STACK_SPILL)
continue;
reg = &state->spilled_regs[i / BPF_REG_SIZE];
if (reg->type != PTR_TO_PACKET &&
reg->type != PTR_TO_PACKET_END)
continue;
reg->type = UNKNOWN_VALUE;
reg->imm = 0;
}
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
static int check_call(struct verifier_env *env, int func_id)
{
struct verifier_state *state = &env->cur_state;
const struct bpf_func_proto *fn = NULL;
struct reg_state *regs = state->regs;
struct reg_state *reg;
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
struct bpf_call_arg_meta meta;
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
bool changes_data;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
int i, err;
/* find function prototype */
if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID) {
verbose("invalid func %d\n", func_id);
return -EINVAL;
}
if (env->prog->aux->ops->get_func_proto)
fn = env->prog->aux->ops->get_func_proto(func_id);
if (!fn) {
verbose("unknown func %d\n", func_id);
return -EINVAL;
}
/* eBPF programs must be GPL compatible to use GPL-ed functions */
ebpf: move read-only fields to bpf_prog and shrink bpf_prog_aux is_gpl_compatible and prog_type should be moved directly into bpf_prog as they stay immutable during bpf_prog's lifetime, are core attributes and they can be locked as read-only later on via bpf_prog_select_runtime(). With a bit of rearranging, this also allows us to shrink bpf_prog_aux to exactly 1 cacheline. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-01 19:31:47 +08:00
if (!env->prog->gpl_compatible && fn->gpl_only) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("cannot call GPL only function from proprietary program\n");
return -EINVAL;
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
changes_data = bpf_helper_changes_skb_data(fn->func);
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
memset(&meta, 0, sizeof(meta));
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
/* We only support one arg being in raw mode at the moment, which
* is sufficient for the helper functions we have right now.
*/
err = check_raw_mode(fn);
if (err) {
verbose("kernel subsystem misconfigured func %d\n", func_id);
return err;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* check args */
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
err = check_func_arg(env, BPF_REG_1, fn->arg1_type, &meta);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (err)
return err;
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
err = check_func_arg(env, BPF_REG_2, fn->arg2_type, &meta);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (err)
return err;
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
err = check_func_arg(env, BPF_REG_3, fn->arg3_type, &meta);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (err)
return err;
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
err = check_func_arg(env, BPF_REG_4, fn->arg4_type, &meta);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (err)
return err;
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
err = check_func_arg(env, BPF_REG_5, fn->arg5_type, &meta);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (err)
return err;
bpf, verifier: add ARG_PTR_TO_RAW_STACK type When passing buffers from eBPF stack space into a helper function, we have ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure that such buffers are initialized, within boundaries, etc. However, the downside with this is that we have a couple of helper functions such as bpf_skb_load_bytes() that fill out the passed buffer in the expected success case anyway, so zero initializing them prior to the helper call is unneeded/wasted instructions in the eBPF program that can be avoided. Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK. The idea is to skip the STACK_MISC check in check_stack_boundary() and color the related stack slots as STACK_MISC after we checked all call arguments. Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of the helper function will fill the provided buffer area, so that we cannot leak any uninitialized stack memory. This f.e. means that error paths need to memset() the buffers, but the expected fast-path doesn't have to do this anymore. Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK argument, we can keep it simple and don't need to check for multiple areas. Should in future such a use-case really appear, we have check_raw_mode() that will make sure we implement support for it first. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:51 +08:00
/* Mark slots with STACK_MISC in case of raw mode, stack offset
* is inferred from register state.
*/
for (i = 0; i < meta.access_size; i++) {
err = check_mem_access(env, meta.regno, i, BPF_B, BPF_WRITE, -1);
if (err)
return err;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* reset caller saved regs */
for (i = 0; i < CALLER_SAVED_REGS; i++) {
reg = regs + caller_saved[i];
reg->type = NOT_INIT;
reg->imm = 0;
}
/* update return register */
if (fn->ret_type == RET_INTEGER) {
regs[BPF_REG_0].type = UNKNOWN_VALUE;
} else if (fn->ret_type == RET_VOID) {
regs[BPF_REG_0].type = NOT_INIT;
} else if (fn->ret_type == RET_PTR_TO_MAP_VALUE_OR_NULL) {
regs[BPF_REG_0].type = PTR_TO_MAP_VALUE_OR_NULL;
/* remember map_ptr, so that check_map_access()
* can check 'value_size' boundary of memory access
* to map element returned from bpf_map_lookup_elem()
*/
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
if (meta.map_ptr == NULL) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("kernel subsystem misconfigured verifier\n");
return -EINVAL;
}
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
regs[BPF_REG_0].map_ptr = meta.map_ptr;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else {
verbose("unknown return type %d of func %d\n",
fn->ret_type, func_id);
return -EINVAL;
}
bpf: allow bpf programs to tail-call other bpf programs introduce bpf_tail_call(ctx, &jmp_table, index) helper function which can be used from BPF programs like: int bpf_prog(struct pt_regs *ctx) { ... bpf_tail_call(ctx, &jmp_table, index); ... } that is roughly equivalent to: int bpf_prog(struct pt_regs *ctx) { ... if (jmp_table[index]) return (*jmp_table[index])(ctx); ... } The important detail that it's not a normal call, but a tail call. The kernel stack is precious, so this helper reuses the current stack frame and jumps into another BPF program without adding extra call frame. It's trivially done in interpreter and a bit trickier in JITs. In case of x64 JIT the bigger part of generated assembler prologue is common for all programs, so it is simply skipped while jumping. Other JITs can do similar prologue-skipping optimization or do stack unwind before jumping into the next program. bpf_tail_call() arguments: ctx - context pointer jmp_table - one of BPF_MAP_TYPE_PROG_ARRAY maps used as the jump table index - index in the jump table Since all BPF programs are idenitified by file descriptor, user space need to populate the jmp_table with FDs of other BPF programs. If jmp_table[index] is empty the bpf_tail_call() doesn't jump anywhere and program execution continues as normal. New BPF_MAP_TYPE_PROG_ARRAY map type is introduced so that user space can populate this jmp_table array with FDs of other bpf programs. Programs can share the same jmp_table array or use multiple jmp_tables. The chain of tail calls can form unpredictable dynamic loops therefore tail_call_cnt is used to limit the number of calls and currently is set to 32. Use cases: Acked-by: Daniel Borkmann <daniel@iogearbox.net> ========== - simplify complex programs by splitting them into a sequence of small programs - dispatch routine For tracing and future seccomp the program may be triggered on all system calls, but processing of syscall arguments will be different. It's more efficient to implement them as: int syscall_entry(struct seccomp_data *ctx) { bpf_tail_call(ctx, &syscall_jmp_table, ctx->nr /* syscall number */); ... default: process unknown syscall ... } int sys_write_event(struct seccomp_data *ctx) {...} int sys_read_event(struct seccomp_data *ctx) {...} syscall_jmp_table[__NR_write] = sys_write_event; syscall_jmp_table[__NR_read] = sys_read_event; For networking the program may call into different parsers depending on packet format, like: int packet_parser(struct __sk_buff *skb) { ... parse L2, L3 here ... __u8 ipproto = load_byte(skb, ... offsetof(struct iphdr, protocol)); bpf_tail_call(skb, &ipproto_jmp_table, ipproto); ... default: process unknown protocol ... } int parse_tcp(struct __sk_buff *skb) {...} int parse_udp(struct __sk_buff *skb) {...} ipproto_jmp_table[IPPROTO_TCP] = parse_tcp; ipproto_jmp_table[IPPROTO_UDP] = parse_udp; - for TC use case, bpf_tail_call() allows to implement reclassify-like logic - bpf_map_update_elem/delete calls into BPF_MAP_TYPE_PROG_ARRAY jump table are atomic, so user space can build chains of BPF programs on the fly Implementation details: ======================= - high performance of bpf_tail_call() is the goal. It could have been implemented without JIT changes as a wrapper on top of BPF_PROG_RUN() macro, but with two downsides: . all programs would have to pay performance penalty for this feature and tail call itself would be slower, since mandatory stack unwind, return, stack allocate would be done for every tailcall. . tailcall would be limited to programs running preempt_disabled, since generic 'void *ctx' doesn't have room for 'tail_call_cnt' and it would need to be either global per_cpu variable accessed by helper and by wrapper or global variable protected by locks. In this implementation x64 JIT bypasses stack unwind and jumps into the callee program after prologue. - bpf_prog_array_compatible() ensures that prog_type of callee and caller are the same and JITed/non-JITed flag is the same, since calling JITed program from non-JITed is invalid, since stack frames are different. Similarly calling kprobe type program from socket type program is invalid. - jump table is implemented as BPF_MAP_TYPE_PROG_ARRAY to reuse 'map' abstraction, its user space API and all of verifier logic. It's in the existing arraymap.c file, since several functions are shared with regular array map. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-05-20 07:59:03 +08:00
bpf, verifier: add bpf_call_arg_meta for passing meta data Currently, when the verifier checks calls in check_call() function, we call check_func_arg() for all 5 arguments e.g. to make sure expected types are correct. In some cases, we collect meta data (here: map pointer) to perform additional checks such as checking stack boundary on key/value sizes for subsequent arguments. As we're going to extend the meta data, add a generic struct bpf_call_arg_meta that we can use for passing into check_func_arg(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 06:10:50 +08:00
err = check_map_func_compatibility(meta.map_ptr, func_id);
bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter According to the perf_event_map_fd and index, the function bpf_perf_event_read() can convert the corresponding map value to the pointer to struct perf_event and return the Hardware PMU counter value. Signed-off-by: Kaixu Xia <xiakaixu@huawei.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-08-06 15:02:35 +08:00
if (err)
return err;
bpf: allow bpf programs to tail-call other bpf programs introduce bpf_tail_call(ctx, &jmp_table, index) helper function which can be used from BPF programs like: int bpf_prog(struct pt_regs *ctx) { ... bpf_tail_call(ctx, &jmp_table, index); ... } that is roughly equivalent to: int bpf_prog(struct pt_regs *ctx) { ... if (jmp_table[index]) return (*jmp_table[index])(ctx); ... } The important detail that it's not a normal call, but a tail call. The kernel stack is precious, so this helper reuses the current stack frame and jumps into another BPF program without adding extra call frame. It's trivially done in interpreter and a bit trickier in JITs. In case of x64 JIT the bigger part of generated assembler prologue is common for all programs, so it is simply skipped while jumping. Other JITs can do similar prologue-skipping optimization or do stack unwind before jumping into the next program. bpf_tail_call() arguments: ctx - context pointer jmp_table - one of BPF_MAP_TYPE_PROG_ARRAY maps used as the jump table index - index in the jump table Since all BPF programs are idenitified by file descriptor, user space need to populate the jmp_table with FDs of other BPF programs. If jmp_table[index] is empty the bpf_tail_call() doesn't jump anywhere and program execution continues as normal. New BPF_MAP_TYPE_PROG_ARRAY map type is introduced so that user space can populate this jmp_table array with FDs of other bpf programs. Programs can share the same jmp_table array or use multiple jmp_tables. The chain of tail calls can form unpredictable dynamic loops therefore tail_call_cnt is used to limit the number of calls and currently is set to 32. Use cases: Acked-by: Daniel Borkmann <daniel@iogearbox.net> ========== - simplify complex programs by splitting them into a sequence of small programs - dispatch routine For tracing and future seccomp the program may be triggered on all system calls, but processing of syscall arguments will be different. It's more efficient to implement them as: int syscall_entry(struct seccomp_data *ctx) { bpf_tail_call(ctx, &syscall_jmp_table, ctx->nr /* syscall number */); ... default: process unknown syscall ... } int sys_write_event(struct seccomp_data *ctx) {...} int sys_read_event(struct seccomp_data *ctx) {...} syscall_jmp_table[__NR_write] = sys_write_event; syscall_jmp_table[__NR_read] = sys_read_event; For networking the program may call into different parsers depending on packet format, like: int packet_parser(struct __sk_buff *skb) { ... parse L2, L3 here ... __u8 ipproto = load_byte(skb, ... offsetof(struct iphdr, protocol)); bpf_tail_call(skb, &ipproto_jmp_table, ipproto); ... default: process unknown protocol ... } int parse_tcp(struct __sk_buff *skb) {...} int parse_udp(struct __sk_buff *skb) {...} ipproto_jmp_table[IPPROTO_TCP] = parse_tcp; ipproto_jmp_table[IPPROTO_UDP] = parse_udp; - for TC use case, bpf_tail_call() allows to implement reclassify-like logic - bpf_map_update_elem/delete calls into BPF_MAP_TYPE_PROG_ARRAY jump table are atomic, so user space can build chains of BPF programs on the fly Implementation details: ======================= - high performance of bpf_tail_call() is the goal. It could have been implemented without JIT changes as a wrapper on top of BPF_PROG_RUN() macro, but with two downsides: . all programs would have to pay performance penalty for this feature and tail call itself would be slower, since mandatory stack unwind, return, stack allocate would be done for every tailcall. . tailcall would be limited to programs running preempt_disabled, since generic 'void *ctx' doesn't have room for 'tail_call_cnt' and it would need to be either global per_cpu variable accessed by helper and by wrapper or global variable protected by locks. In this implementation x64 JIT bypasses stack unwind and jumps into the callee program after prologue. - bpf_prog_array_compatible() ensures that prog_type of callee and caller are the same and JITed/non-JITed flag is the same, since calling JITed program from non-JITed is invalid, since stack frames are different. Similarly calling kprobe type program from socket type program is invalid. - jump table is implemented as BPF_MAP_TYPE_PROG_ARRAY to reuse 'map' abstraction, its user space API and all of verifier logic. It's in the existing arraymap.c file, since several functions are shared with regular array map. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-05-20 07:59:03 +08:00
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
if (changes_data)
clear_all_pkt_pointers(env);
return 0;
}
static int check_packet_ptr_add(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *dst_reg = &regs[insn->dst_reg];
struct reg_state *src_reg = &regs[insn->src_reg];
bpf: teach verifier to recognize imm += ptr pattern Humans don't write C code like: u8 *ptr = skb->data; int imm = 4; imm += ptr; but from llvm backend point of view 'imm' and 'ptr' are registers and imm += ptr may be preferred vs ptr += imm depending which register value will be used further in the code, while verifier can only recognize ptr += imm. That caused small unrelated changes in the C code of the bpf program to trigger rejection by the verifier. Therefore teach the verifier to recognize both ptr += imm and imm += ptr. For example: when R6=pkt(id=0,off=0,r=62) R7=imm22 after r7 += r6 instruction will be R6=pkt(id=0,off=0,r=62) R7=pkt(id=0,off=22,r=62) Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-20 09:17:14 +08:00
struct reg_state tmp_reg;
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
s32 imm;
if (BPF_SRC(insn->code) == BPF_K) {
/* pkt_ptr += imm */
imm = insn->imm;
add_imm:
if (imm <= 0) {
verbose("addition of negative constant to packet pointer is not allowed\n");
return -EACCES;
}
if (imm >= MAX_PACKET_OFF ||
imm + dst_reg->off >= MAX_PACKET_OFF) {
verbose("constant %d is too large to add to packet pointer\n",
imm);
return -EACCES;
}
/* a constant was added to pkt_ptr.
* Remember it while keeping the same 'id'
*/
dst_reg->off += imm;
} else {
bpf: teach verifier to recognize imm += ptr pattern Humans don't write C code like: u8 *ptr = skb->data; int imm = 4; imm += ptr; but from llvm backend point of view 'imm' and 'ptr' are registers and imm += ptr may be preferred vs ptr += imm depending which register value will be used further in the code, while verifier can only recognize ptr += imm. That caused small unrelated changes in the C code of the bpf program to trigger rejection by the verifier. Therefore teach the verifier to recognize both ptr += imm and imm += ptr. For example: when R6=pkt(id=0,off=0,r=62) R7=imm22 after r7 += r6 instruction will be R6=pkt(id=0,off=0,r=62) R7=pkt(id=0,off=22,r=62) Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-20 09:17:14 +08:00
if (src_reg->type == PTR_TO_PACKET) {
/* R6=pkt(id=0,off=0,r=62) R7=imm22; r7 += r6 */
tmp_reg = *dst_reg; /* save r7 state */
*dst_reg = *src_reg; /* copy pkt_ptr state r6 into r7 */
src_reg = &tmp_reg; /* pretend it's src_reg state */
/* if the checks below reject it, the copy won't matter,
* since we're rejecting the whole program. If all ok,
* then imm22 state will be added to r7
* and r7 will be pkt(id=0,off=22,r=62) while
* r6 will stay as pkt(id=0,off=0,r=62)
*/
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
if (src_reg->type == CONST_IMM) {
/* pkt_ptr += reg where reg is known constant */
imm = src_reg->imm;
goto add_imm;
}
/* disallow pkt_ptr += reg
* if reg is not uknown_value with guaranteed zero upper bits
* otherwise pkt_ptr may overflow and addition will become
* subtraction which is not allowed
*/
if (src_reg->type != UNKNOWN_VALUE) {
verbose("cannot add '%s' to ptr_to_packet\n",
reg_type_str[src_reg->type]);
return -EACCES;
}
if (src_reg->imm < 48) {
verbose("cannot add integer value with %lld upper zero bits to ptr_to_packet\n",
src_reg->imm);
return -EACCES;
}
/* dst_reg stays as pkt_ptr type and since some positive
* integer value was added to the pointer, increment its 'id'
*/
dst_reg->id++;
/* something was added to pkt_ptr, set range and off to zero */
dst_reg->off = 0;
dst_reg->range = 0;
}
return 0;
}
static int evaluate_reg_alu(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *dst_reg = &regs[insn->dst_reg];
u8 opcode = BPF_OP(insn->code);
s64 imm_log2;
/* for type == UNKNOWN_VALUE:
* imm > 0 -> number of zero upper bits
* imm == 0 -> don't track which is the same as all bits can be non-zero
*/
if (BPF_SRC(insn->code) == BPF_X) {
struct reg_state *src_reg = &regs[insn->src_reg];
if (src_reg->type == UNKNOWN_VALUE && src_reg->imm > 0 &&
dst_reg->imm && opcode == BPF_ADD) {
/* dreg += sreg
* where both have zero upper bits. Adding them
* can only result making one more bit non-zero
* in the larger value.
* Ex. 0xffff (imm=48) + 1 (imm=63) = 0x10000 (imm=47)
* 0xffff (imm=48) + 0xffff = 0x1fffe (imm=47)
*/
dst_reg->imm = min(dst_reg->imm, src_reg->imm);
dst_reg->imm--;
return 0;
}
if (src_reg->type == CONST_IMM && src_reg->imm > 0 &&
dst_reg->imm && opcode == BPF_ADD) {
/* dreg += sreg
* where dreg has zero upper bits and sreg is const.
* Adding them can only result making one more bit
* non-zero in the larger value.
*/
imm_log2 = __ilog2_u64((long long)src_reg->imm);
dst_reg->imm = min(dst_reg->imm, 63 - imm_log2);
dst_reg->imm--;
return 0;
}
/* all other cases non supported yet, just mark dst_reg */
dst_reg->imm = 0;
return 0;
}
/* sign extend 32-bit imm into 64-bit to make sure that
* negative values occupy bit 63. Note ilog2() would have
* been incorrect, since sizeof(insn->imm) == 4
*/
imm_log2 = __ilog2_u64((long long)insn->imm);
if (dst_reg->imm && opcode == BPF_LSH) {
/* reg <<= imm
* if reg was a result of 2 byte load, then its imm == 48
* which means that upper 48 bits are zero and shifting this reg
* left by 4 would mean that upper 44 bits are still zero
*/
dst_reg->imm -= insn->imm;
} else if (dst_reg->imm && opcode == BPF_MUL) {
/* reg *= imm
* if multiplying by 14 subtract 4
* This is conservative calculation of upper zero bits.
* It's not trying to special case insn->imm == 1 or 0 cases
*/
dst_reg->imm -= imm_log2 + 1;
} else if (opcode == BPF_AND) {
/* reg &= imm */
dst_reg->imm = 63 - imm_log2;
} else if (dst_reg->imm && opcode == BPF_ADD) {
/* reg += imm */
dst_reg->imm = min(dst_reg->imm, 63 - imm_log2);
dst_reg->imm--;
} else if (opcode == BPF_RSH) {
/* reg >>= imm
* which means that after right shift, upper bits will be zero
* note that verifier already checked that
* 0 <= imm < 64 for shift insn
*/
dst_reg->imm += insn->imm;
if (unlikely(dst_reg->imm > 64))
/* some dumb code did:
* r2 = *(u32 *)mem;
* r2 >>= 32;
* and all bits are zero now */
dst_reg->imm = 64;
} else {
/* all other alu ops, means that we don't know what will
* happen to the value, mark it with unknown number of zero bits
*/
dst_reg->imm = 0;
}
if (dst_reg->imm < 0) {
/* all 64 bits of the register can contain non-zero bits
* and such value cannot be added to ptr_to_packet, since it
* may overflow, mark it as unknown to avoid further eval
*/
dst_reg->imm = 0;
}
return 0;
}
static int evaluate_reg_imm_alu(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
struct reg_state *dst_reg = &regs[insn->dst_reg];
struct reg_state *src_reg = &regs[insn->src_reg];
u8 opcode = BPF_OP(insn->code);
/* dst_reg->type == CONST_IMM here, simulate execution of 'add' insn.
* Don't care about overflow or negative values, just add them
*/
if (opcode == BPF_ADD && BPF_SRC(insn->code) == BPF_K)
dst_reg->imm += insn->imm;
else if (opcode == BPF_ADD && BPF_SRC(insn->code) == BPF_X &&
src_reg->type == CONST_IMM)
dst_reg->imm += src_reg->imm;
else
mark_reg_unknown_value(regs, insn->dst_reg);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return 0;
}
/* check validity of 32-bit and 64-bit arithmetic operations */
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
static int check_alu_op(struct verifier_env *env, struct bpf_insn *insn)
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
{
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
struct reg_state *regs = env->cur_state.regs, *dst_reg;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
u8 opcode = BPF_OP(insn->code);
int err;
if (opcode == BPF_END || opcode == BPF_NEG) {
if (opcode == BPF_NEG) {
if (BPF_SRC(insn->code) != 0 ||
insn->src_reg != BPF_REG_0 ||
insn->off != 0 || insn->imm != 0) {
verbose("BPF_NEG uses reserved fields\n");
return -EINVAL;
}
} else {
if (insn->src_reg != BPF_REG_0 || insn->off != 0 ||
(insn->imm != 16 && insn->imm != 32 && insn->imm != 64)) {
verbose("BPF_END uses reserved fields\n");
return -EINVAL;
}
}
/* check src operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer arithmetic prohibited\n",
insn->dst_reg);
return -EACCES;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* check dest operand */
err = check_reg_arg(regs, insn->dst_reg, DST_OP);
if (err)
return err;
} else if (opcode == BPF_MOV) {
if (BPF_SRC(insn->code) == BPF_X) {
if (insn->imm != 0 || insn->off != 0) {
verbose("BPF_MOV uses reserved fields\n");
return -EINVAL;
}
/* check src operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
} else {
if (insn->src_reg != BPF_REG_0 || insn->off != 0) {
verbose("BPF_MOV uses reserved fields\n");
return -EINVAL;
}
}
/* check dest operand */
err = check_reg_arg(regs, insn->dst_reg, DST_OP);
if (err)
return err;
if (BPF_SRC(insn->code) == BPF_X) {
if (BPF_CLASS(insn->code) == BPF_ALU64) {
/* case: R1 = R2
* copy register state to dest reg
*/
regs[insn->dst_reg] = regs[insn->src_reg];
} else {
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
if (is_pointer_value(env, insn->src_reg)) {
verbose("R%d partial copy of pointer\n",
insn->src_reg);
return -EACCES;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
regs[insn->dst_reg].type = UNKNOWN_VALUE;
regs[insn->dst_reg].map_ptr = NULL;
}
} else {
/* case: R = imm
* remember the value we stored into this reg
*/
regs[insn->dst_reg].type = CONST_IMM;
regs[insn->dst_reg].imm = insn->imm;
}
} else if (opcode > BPF_END) {
verbose("invalid BPF_ALU opcode %x\n", opcode);
return -EINVAL;
} else { /* all other ALU ops: and, sub, xor, add, ... */
if (BPF_SRC(insn->code) == BPF_X) {
if (insn->imm != 0 || insn->off != 0) {
verbose("BPF_ALU uses reserved fields\n");
return -EINVAL;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
} else {
if (insn->src_reg != BPF_REG_0 || insn->off != 0) {
verbose("BPF_ALU uses reserved fields\n");
return -EINVAL;
}
}
/* check src2 operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
if ((opcode == BPF_MOD || opcode == BPF_DIV) &&
BPF_SRC(insn->code) == BPF_K && insn->imm == 0) {
verbose("div by zero\n");
return -EINVAL;
}
net: bpf: reject invalid shifts On ARM64, a BUG() is triggered in the eBPF JIT if a filter with a constant shift that can't be encoded in the immediate field of the UBFM/SBFM instructions is passed to the JIT. Since these shifts amounts, which are negative or >= regsize, are invalid, reject them in the eBPF verifier and the classic BPF filter checker, for all architectures. Signed-off-by: Rabin Vincent <rabin@rab.in> Acked-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-01-13 03:17:08 +08:00
if ((opcode == BPF_LSH || opcode == BPF_RSH ||
opcode == BPF_ARSH) && BPF_SRC(insn->code) == BPF_K) {
int size = BPF_CLASS(insn->code) == BPF_ALU64 ? 64 : 32;
if (insn->imm < 0 || insn->imm >= size) {
verbose("invalid shift %d\n", insn->imm);
return -EINVAL;
}
}
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
/* check dest operand */
err = check_reg_arg(regs, insn->dst_reg, DST_OP_NO_MARK);
if (err)
return err;
dst_reg = &regs[insn->dst_reg];
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* pattern match 'bpf_add Rx, imm' instruction */
if (opcode == BPF_ADD && BPF_CLASS(insn->code) == BPF_ALU64 &&
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
dst_reg->type == FRAME_PTR && BPF_SRC(insn->code) == BPF_K) {
dst_reg->type = PTR_TO_STACK;
dst_reg->imm = insn->imm;
return 0;
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
} else if (opcode == BPF_ADD &&
BPF_CLASS(insn->code) == BPF_ALU64 &&
bpf: teach verifier to recognize imm += ptr pattern Humans don't write C code like: u8 *ptr = skb->data; int imm = 4; imm += ptr; but from llvm backend point of view 'imm' and 'ptr' are registers and imm += ptr may be preferred vs ptr += imm depending which register value will be used further in the code, while verifier can only recognize ptr += imm. That caused small unrelated changes in the C code of the bpf program to trigger rejection by the verifier. Therefore teach the verifier to recognize both ptr += imm and imm += ptr. For example: when R6=pkt(id=0,off=0,r=62) R7=imm22 after r7 += r6 instruction will be R6=pkt(id=0,off=0,r=62) R7=pkt(id=0,off=22,r=62) Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-20 09:17:14 +08:00
(dst_reg->type == PTR_TO_PACKET ||
(BPF_SRC(insn->code) == BPF_X &&
regs[insn->src_reg].type == PTR_TO_PACKET))) {
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
/* ptr_to_packet += K|X */
return check_packet_ptr_add(env, insn);
} else if (BPF_CLASS(insn->code) == BPF_ALU64 &&
dst_reg->type == UNKNOWN_VALUE &&
env->allow_ptr_leaks) {
/* unknown += K|X */
return evaluate_reg_alu(env, insn);
} else if (BPF_CLASS(insn->code) == BPF_ALU64 &&
dst_reg->type == CONST_IMM &&
env->allow_ptr_leaks) {
/* reg_imm += K|X */
return evaluate_reg_imm_alu(env, insn);
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
} else if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer arithmetic prohibited\n",
insn->dst_reg);
return -EACCES;
} else if (BPF_SRC(insn->code) == BPF_X &&
is_pointer_value(env, insn->src_reg)) {
verbose("R%d pointer arithmetic prohibited\n",
insn->src_reg);
return -EACCES;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
/* mark dest operand */
mark_reg_unknown_value(regs, insn->dst_reg);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
}
return 0;
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
static void find_good_pkt_pointers(struct verifier_env *env,
struct reg_state *dst_reg)
{
struct verifier_state *state = &env->cur_state;
struct reg_state *regs = state->regs, *reg;
int i;
/* r2 = r3;
* r2 += 8
* if (r2 > pkt_end) goto somewhere
* r2 == dst_reg, pkt_end == src_reg,
* r2=pkt(id=n,off=8,r=0)
* r3=pkt(id=n,off=0,r=0)
* find register r3 and mark its range as r3=pkt(id=n,off=0,r=8)
* so that range of bytes [r3, r3 + 8) is safe to access
*/
for (i = 0; i < MAX_BPF_REG; i++)
if (regs[i].type == PTR_TO_PACKET && regs[i].id == dst_reg->id)
regs[i].range = dst_reg->off;
for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
if (state->stack_slot_type[i] != STACK_SPILL)
continue;
reg = &state->spilled_regs[i / BPF_REG_SIZE];
if (reg->type == PTR_TO_PACKET && reg->id == dst_reg->id)
reg->range = dst_reg->off;
}
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
static int check_cond_jmp_op(struct verifier_env *env,
struct bpf_insn *insn, int *insn_idx)
{
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
struct reg_state *regs = env->cur_state.regs, *dst_reg;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
struct verifier_state *other_branch;
u8 opcode = BPF_OP(insn->code);
int err;
if (opcode > BPF_EXIT) {
verbose("invalid BPF_JMP opcode %x\n", opcode);
return -EINVAL;
}
if (BPF_SRC(insn->code) == BPF_X) {
if (insn->imm != 0) {
verbose("BPF_JMP uses reserved fields\n");
return -EINVAL;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
if (is_pointer_value(env, insn->src_reg)) {
verbose("R%d pointer comparison prohibited\n",
insn->src_reg);
return -EACCES;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else {
if (insn->src_reg != BPF_REG_0) {
verbose("BPF_JMP uses reserved fields\n");
return -EINVAL;
}
}
/* check src2 operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
dst_reg = &regs[insn->dst_reg];
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* detect if R == 0 where R was initialized to zero earlier */
if (BPF_SRC(insn->code) == BPF_K &&
(opcode == BPF_JEQ || opcode == BPF_JNE) &&
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
dst_reg->type == CONST_IMM && dst_reg->imm == insn->imm) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (opcode == BPF_JEQ) {
/* if (imm == imm) goto pc+off;
* only follow the goto, ignore fall-through
*/
*insn_idx += insn->off;
return 0;
} else {
/* if (imm != imm) goto pc+off;
* only follow fall-through branch, since
* that's where the program will go
*/
return 0;
}
}
other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx);
if (!other_branch)
return -EFAULT;
/* detect if R == 0 where R is returned value from bpf_map_lookup_elem() */
if (BPF_SRC(insn->code) == BPF_K &&
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
insn->imm == 0 && (opcode == BPF_JEQ || opcode == BPF_JNE) &&
dst_reg->type == PTR_TO_MAP_VALUE_OR_NULL) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (opcode == BPF_JEQ) {
/* next fallthrough insn can access memory via
* this register
*/
regs[insn->dst_reg].type = PTR_TO_MAP_VALUE;
/* branch targer cannot access it, since reg == 0 */
bpf: improve verifier state equivalence since UNKNOWN_VALUE type is weaker than CONST_IMM we can un-teach verifier its recognition of constants in conditional branches without affecting safety. Ex: if (reg == 123) { .. here verifier was marking reg->type as CONST_IMM instead keep reg as UNKNOWN_VALUE } Two verifier states with UNKNOWN_VALUE are equivalent, whereas CONST_IMM_X != CONST_IMM_Y, since CONST_IMM is used for stack range verification and other cases. So help search pruning by marking registers as UNKNOWN_VALUE where possible instead of CONST_IMM. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:11 +08:00
mark_reg_unknown_value(other_branch->regs,
insn->dst_reg);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else {
other_branch->regs[insn->dst_reg].type = PTR_TO_MAP_VALUE;
bpf: improve verifier state equivalence since UNKNOWN_VALUE type is weaker than CONST_IMM we can un-teach verifier its recognition of constants in conditional branches without affecting safety. Ex: if (reg == 123) { .. here verifier was marking reg->type as CONST_IMM instead keep reg as UNKNOWN_VALUE } Two verifier states with UNKNOWN_VALUE are equivalent, whereas CONST_IMM_X != CONST_IMM_Y, since CONST_IMM is used for stack range verification and other cases. So help search pruning by marking registers as UNKNOWN_VALUE where possible instead of CONST_IMM. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:11 +08:00
mark_reg_unknown_value(regs, insn->dst_reg);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGT &&
dst_reg->type == PTR_TO_PACKET &&
regs[insn->src_reg].type == PTR_TO_PACKET_END) {
find_good_pkt_pointers(env, dst_reg);
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
} else if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer comparison prohibited\n", insn->dst_reg);
return -EACCES;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
}
if (log_level)
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
print_verifier_state(&env->cur_state);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return 0;
}
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
/* return the map pointer stored inside BPF_LD_IMM64 instruction */
static struct bpf_map *ld_imm64_to_map_ptr(struct bpf_insn *insn)
{
u64 imm64 = ((u64) (u32) insn[0].imm) | ((u64) (u32) insn[1].imm) << 32;
return (struct bpf_map *) (unsigned long) imm64;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* verify BPF_LD_IMM64 instruction */
static int check_ld_imm(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
int err;
if (BPF_SIZE(insn->code) != BPF_DW) {
verbose("invalid BPF_LD_IMM insn\n");
return -EINVAL;
}
if (insn->off != 0) {
verbose("BPF_LD_IMM64 uses reserved fields\n");
return -EINVAL;
}
err = check_reg_arg(regs, insn->dst_reg, DST_OP);
if (err)
return err;
if (insn->src_reg == 0)
/* generic move 64-bit immediate into a register */
return 0;
/* replace_map_fd_with_map_ptr() should have caught bad ld_imm64 */
BUG_ON(insn->src_reg != BPF_PSEUDO_MAP_FD);
regs[insn->dst_reg].type = CONST_PTR_TO_MAP;
regs[insn->dst_reg].map_ptr = ld_imm64_to_map_ptr(insn);
return 0;
}
ebpf: add sched_cls_type and map it to sk_filter's verifier ops As discussed recently and at netconf/netdev01, we want to prevent making bpf_verifier_ops registration available for modules, but have them at a controlled place inside the kernel instead. The reason for this is, that out-of-tree modules can go crazy and define and register any verfifier ops they want, doing all sorts of crap, even bypassing available GPLed eBPF helper functions. We don't want to offer such a shiny playground, of course, but keep strict control to ourselves inside the core kernel. This also encourages us to design eBPF user helpers carefully and generically, so they can be shared among various subsystems using eBPF. For the eBPF traffic classifier (cls_bpf), it's a good start to share the same helper facilities as we currently do in eBPF for socket filters. That way, we have BPF_PROG_TYPE_SCHED_CLS look like it's own type, thus one day if there's a good reason to diverge the set of helper functions from the set available to socket filters, we keep ABI compatibility. In future, we could place all bpf_prog_type_list at a central place, perhaps. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-01 19:31:46 +08:00
static bool may_access_skb(enum bpf_prog_type type)
{
switch (type) {
case BPF_PROG_TYPE_SOCKET_FILTER:
case BPF_PROG_TYPE_SCHED_CLS:
ebpf: add sched_act_type and map it to sk_filter's verifier ops In order to prepare eBPF support for tc action, we need to add sched_act_type, so that the eBPF verifier is aware of what helper function act_bpf may use, that it can load skb data and read out currently available skb fields. This is bascially analogous to 96be4325f443 ("ebpf: add sched_cls_type and map it to sk_filter's verifier ops"). BPF_PROG_TYPE_SCHED_CLS and BPF_PROG_TYPE_SCHED_ACT need to be separate since both will have a different set of functionality in future (classifier vs action), thus we won't run into ABI troubles when the point in time comes to diverge functionality from the classifier. The future plan for act_bpf would be that it will be able to write into skb->data and alter selected fields mirrored in struct __sk_buff. For an initial support, it's sufficient to map it to sk_filter_ops. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Cc: Jiri Pirko <jiri@resnulli.us> Reviewed-by: Jiri Pirko <jiri@resnulli.us> Acked-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-20 22:11:11 +08:00
case BPF_PROG_TYPE_SCHED_ACT:
ebpf: add sched_cls_type and map it to sk_filter's verifier ops As discussed recently and at netconf/netdev01, we want to prevent making bpf_verifier_ops registration available for modules, but have them at a controlled place inside the kernel instead. The reason for this is, that out-of-tree modules can go crazy and define and register any verfifier ops they want, doing all sorts of crap, even bypassing available GPLed eBPF helper functions. We don't want to offer such a shiny playground, of course, but keep strict control to ourselves inside the core kernel. This also encourages us to design eBPF user helpers carefully and generically, so they can be shared among various subsystems using eBPF. For the eBPF traffic classifier (cls_bpf), it's a good start to share the same helper facilities as we currently do in eBPF for socket filters. That way, we have BPF_PROG_TYPE_SCHED_CLS look like it's own type, thus one day if there's a good reason to diverge the set of helper functions from the set available to socket filters, we keep ABI compatibility. In future, we could place all bpf_prog_type_list at a central place, perhaps. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-01 19:31:46 +08:00
return true;
default:
return false;
}
}
bpf: verifier: add checks for BPF_ABS | BPF_IND instructions introduce program type BPF_PROG_TYPE_SOCKET_FILTER that is used for attaching programs to sockets where ctx == skb. add verifier checks for ABS/IND instructions which can only be seen in socket filters, therefore the check: if (env->prog->aux->prog_type != BPF_PROG_TYPE_SOCKET_FILTER) verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n"); Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-02 07:06:34 +08:00
/* verify safety of LD_ABS|LD_IND instructions:
* - they can only appear in the programs where ctx == skb
* - since they are wrappers of function calls, they scratch R1-R5 registers,
* preserve R6-R9, and store return value into R0
*
* Implicit input:
* ctx == skb == R6 == CTX
*
* Explicit input:
* SRC == any register
* IMM == 32-bit immediate
*
* Output:
* R0 - 8/16/32-bit skb data converted to cpu endianness
*/
static int check_ld_abs(struct verifier_env *env, struct bpf_insn *insn)
{
struct reg_state *regs = env->cur_state.regs;
u8 mode = BPF_MODE(insn->code);
struct reg_state *reg;
int i, err;
ebpf: move read-only fields to bpf_prog and shrink bpf_prog_aux is_gpl_compatible and prog_type should be moved directly into bpf_prog as they stay immutable during bpf_prog's lifetime, are core attributes and they can be locked as read-only later on via bpf_prog_select_runtime(). With a bit of rearranging, this also allows us to shrink bpf_prog_aux to exactly 1 cacheline. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-01 19:31:47 +08:00
if (!may_access_skb(env->prog->type)) {
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
verbose("BPF_LD_[ABS|IND] instructions not allowed for this program type\n");
bpf: verifier: add checks for BPF_ABS | BPF_IND instructions introduce program type BPF_PROG_TYPE_SOCKET_FILTER that is used for attaching programs to sockets where ctx == skb. add verifier checks for ABS/IND instructions which can only be seen in socket filters, therefore the check: if (env->prog->aux->prog_type != BPF_PROG_TYPE_SOCKET_FILTER) verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n"); Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-02 07:06:34 +08:00
return -EINVAL;
}
if (insn->dst_reg != BPF_REG_0 || insn->off != 0 ||
bpf/verifier: reject invalid LD_ABS | BPF_DW instruction verifier must check for reserved size bits in instruction opcode and reject BPF_LD | BPF_ABS | BPF_DW and BPF_LD | BPF_IND | BPF_DW instructions, otherwise interpreter will WARN_RATELIMIT on them during execution. Fixes: ddd872bc3098 ("bpf: verifier: add checks for BPF_ABS | BPF_IND instructions") Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-13 01:26:19 +08:00
BPF_SIZE(insn->code) == BPF_DW ||
bpf: verifier: add checks for BPF_ABS | BPF_IND instructions introduce program type BPF_PROG_TYPE_SOCKET_FILTER that is used for attaching programs to sockets where ctx == skb. add verifier checks for ABS/IND instructions which can only be seen in socket filters, therefore the check: if (env->prog->aux->prog_type != BPF_PROG_TYPE_SOCKET_FILTER) verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n"); Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-02 07:06:34 +08:00
(mode == BPF_ABS && insn->src_reg != BPF_REG_0)) {
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
verbose("BPF_LD_[ABS|IND] uses reserved fields\n");
bpf: verifier: add checks for BPF_ABS | BPF_IND instructions introduce program type BPF_PROG_TYPE_SOCKET_FILTER that is used for attaching programs to sockets where ctx == skb. add verifier checks for ABS/IND instructions which can only be seen in socket filters, therefore the check: if (env->prog->aux->prog_type != BPF_PROG_TYPE_SOCKET_FILTER) verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n"); Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-02 07:06:34 +08:00
return -EINVAL;
}
/* check whether implicit source operand (register R6) is readable */
err = check_reg_arg(regs, BPF_REG_6, SRC_OP);
if (err)
return err;
if (regs[BPF_REG_6].type != PTR_TO_CTX) {
verbose("at the time of BPF_LD_ABS|IND R6 != pointer to skb\n");
return -EINVAL;
}
if (mode == BPF_IND) {
/* check explicit source operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
}
/* reset caller saved regs to unreadable */
for (i = 0; i < CALLER_SAVED_REGS; i++) {
reg = regs + caller_saved[i];
reg->type = NOT_INIT;
reg->imm = 0;
}
/* mark destination R0 register as readable, since it contains
* the value fetched from the packet
*/
regs[BPF_REG_0].type = UNKNOWN_VALUE;
return 0;
}
bpf: verifier (add branch/goto checks) check that control flow graph of eBPF program is a directed acyclic graph check_cfg() does: - detect loops - detect unreachable instructions - check that program terminates with BPF_EXIT insn - check that all branches are within program boundary Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:05 +08:00
/* non-recursive DFS pseudo code
* 1 procedure DFS-iterative(G,v):
* 2 label v as discovered
* 3 let S be a stack
* 4 S.push(v)
* 5 while S is not empty
* 6 t <- S.pop()
* 7 if t is what we're looking for:
* 8 return t
* 9 for all edges e in G.adjacentEdges(t) do
* 10 if edge e is already labelled
* 11 continue with the next edge
* 12 w <- G.adjacentVertex(t,e)
* 13 if vertex w is not discovered and not explored
* 14 label e as tree-edge
* 15 label w as discovered
* 16 S.push(w)
* 17 continue at 5
* 18 else if vertex w is discovered
* 19 label e as back-edge
* 20 else
* 21 // vertex w is explored
* 22 label e as forward- or cross-edge
* 23 label t as explored
* 24 S.pop()
*
* convention:
* 0x10 - discovered
* 0x11 - discovered and fall-through edge labelled
* 0x12 - discovered and fall-through and branch edges labelled
* 0x20 - explored
*/
enum {
DISCOVERED = 0x10,
EXPLORED = 0x20,
FALLTHROUGH = 1,
BRANCH = 2,
};
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
#define STATE_LIST_MARK ((struct verifier_state_list *) -1L)
bpf: verifier (add branch/goto checks) check that control flow graph of eBPF program is a directed acyclic graph check_cfg() does: - detect loops - detect unreachable instructions - check that program terminates with BPF_EXIT insn - check that all branches are within program boundary Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:05 +08:00
static int *insn_stack; /* stack of insns to process */
static int cur_stack; /* current stack index */
static int *insn_state;
/* t, w, e - match pseudo-code above:
* t - index of current instruction
* w - next instruction
* e - edge
*/
static int push_insn(int t, int w, int e, struct verifier_env *env)
{
if (e == FALLTHROUGH && insn_state[t] >= (DISCOVERED | FALLTHROUGH))
return 0;
if (e == BRANCH && insn_state[t] >= (DISCOVERED | BRANCH))
return 0;
if (w < 0 || w >= env->prog->len) {
verbose("jump out of range from insn %d to %d\n", t, w);
return -EINVAL;
}
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
if (e == BRANCH)
/* mark branch target for state pruning */
env->explored_states[w] = STATE_LIST_MARK;
bpf: verifier (add branch/goto checks) check that control flow graph of eBPF program is a directed acyclic graph check_cfg() does: - detect loops - detect unreachable instructions - check that program terminates with BPF_EXIT insn - check that all branches are within program boundary Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:05 +08:00
if (insn_state[w] == 0) {
/* tree-edge */
insn_state[t] = DISCOVERED | e;
insn_state[w] = DISCOVERED;
if (cur_stack >= env->prog->len)
return -E2BIG;
insn_stack[cur_stack++] = w;
return 1;
} else if ((insn_state[w] & 0xF0) == DISCOVERED) {
verbose("back-edge from insn %d to %d\n", t, w);
return -EINVAL;
} else if (insn_state[w] == EXPLORED) {
/* forward- or cross-edge */
insn_state[t] = DISCOVERED | e;
} else {
verbose("insn state internal bug\n");
return -EFAULT;
}
return 0;
}
/* non-recursive depth-first-search to detect loops in BPF program
* loop == back-edge in directed graph
*/
static int check_cfg(struct verifier_env *env)
{
struct bpf_insn *insns = env->prog->insnsi;
int insn_cnt = env->prog->len;
int ret = 0;
int i, t;
insn_state = kcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
if (!insn_state)
return -ENOMEM;
insn_stack = kcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
if (!insn_stack) {
kfree(insn_state);
return -ENOMEM;
}
insn_state[0] = DISCOVERED; /* mark 1st insn as discovered */
insn_stack[0] = 0; /* 0 is the first instruction */
cur_stack = 1;
peek_stack:
if (cur_stack == 0)
goto check_state;
t = insn_stack[cur_stack - 1];
if (BPF_CLASS(insns[t].code) == BPF_JMP) {
u8 opcode = BPF_OP(insns[t].code);
if (opcode == BPF_EXIT) {
goto mark_explored;
} else if (opcode == BPF_CALL) {
ret = push_insn(t, t + 1, FALLTHROUGH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
bpf, verifier: further improve search pruning The verifier needs to go through every path of the program in order to check that it terminates safely, which can be quite a lot of instructions that need to be processed f.e. in cases with more branchy programs. With search pruning from f1bca824dabb ("bpf: add search pruning optimization to verifier") the search space can already be reduced significantly when the verifier detects that a previously walked path with same register and stack contents terminated already (see verifier's states_equal()), so the search can skip walking those states. When working with larger programs of > ~2000 (out of max 4096) insns, we found that the current limit of 32k instructions is easily hit. For example, a case we ran into is that the search space cannot be pruned due to branches at the beginning of the program that make use of certain stack space slots (STACK_MISC), which are never used in the remaining program (STACK_INVALID). Therefore, the verifier needs to walk paths for the slots in STACK_INVALID state, but also all remaining paths with a stack structure, where the slots are in STACK_MISC, which can nearly double the search space needed. After various experiments, we find that a limit of 64k processed insns is a more reasonable choice when dealing with larger programs in practice. This still allows to reject extreme crafted cases that can have a much higher complexity (f.e. > ~300k) within the 4096 insns limit due to search pruning not being able to take effect. Furthermore, we found that a lot of states can be pruned after a call instruction, f.e. we were able to reduce the search state by ~35% in some cases with this heuristic, trade-off is to keep a bit more states in env->explored_states. Usually, call instructions have a number of preceding register assignments and/or stack stores, where search pruning has a better chance to suceed in states_equal() test. The current code marks the branch targets with STATE_LIST_MARK in case of conditional jumps, and the next (t + 1) instruction in case of unconditional jump so that f.e. a backjump will walk it. We also did experiments with using t + insns[t].off + 1 as a marker in the unconditionally jump case instead of t + 1 with the rationale that these two branches of execution that converge after the label might have more potential of pruning. We found that it was a bit better, but not necessarily significantly better than the current state, perhaps also due to clang not generating back jumps often. Hence, we left that as is for now. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-06 04:33:17 +08:00
if (t + 1 < insn_cnt)
env->explored_states[t + 1] = STATE_LIST_MARK;
bpf: verifier (add branch/goto checks) check that control flow graph of eBPF program is a directed acyclic graph check_cfg() does: - detect loops - detect unreachable instructions - check that program terminates with BPF_EXIT insn - check that all branches are within program boundary Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:05 +08:00
} else if (opcode == BPF_JA) {
if (BPF_SRC(insns[t].code) != BPF_K) {
ret = -EINVAL;
goto err_free;
}
/* unconditional jump with single edge */
ret = push_insn(t, t + insns[t].off + 1,
FALLTHROUGH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
/* tell verifier to check for equivalent states
* after every call and jump
*/
bpf: fix verifier memory corruption Due to missing bounds check the DAG pass of the BPF verifier can corrupt the memory which can cause random crashes during program loading: [8.449451] BUG: unable to handle kernel paging request at ffffffffffffffff [8.451293] IP: [<ffffffff811de33d>] kmem_cache_alloc_trace+0x8d/0x2f0 [8.452329] Oops: 0000 [#1] SMP [8.452329] Call Trace: [8.452329] [<ffffffff8116cc82>] bpf_check+0x852/0x2000 [8.452329] [<ffffffff8116b7e4>] bpf_prog_load+0x1e4/0x310 [8.452329] [<ffffffff811b190f>] ? might_fault+0x5f/0xb0 [8.452329] [<ffffffff8116c206>] SyS_bpf+0x806/0xa30 Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier") Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-15 06:57:13 +08:00
if (t + 1 < insn_cnt)
env->explored_states[t + 1] = STATE_LIST_MARK;
bpf: verifier (add branch/goto checks) check that control flow graph of eBPF program is a directed acyclic graph check_cfg() does: - detect loops - detect unreachable instructions - check that program terminates with BPF_EXIT insn - check that all branches are within program boundary Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:05 +08:00
} else {
/* conditional jump with two edges */
ret = push_insn(t, t + 1, FALLTHROUGH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
ret = push_insn(t, t + insns[t].off + 1, BRANCH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
}
} else {
/* all other non-branch instructions with single
* fall-through edge
*/
ret = push_insn(t, t + 1, FALLTHROUGH, env);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
}
mark_explored:
insn_state[t] = EXPLORED;
if (cur_stack-- <= 0) {
verbose("pop stack internal bug\n");
ret = -EFAULT;
goto err_free;
}
goto peek_stack;
check_state:
for (i = 0; i < insn_cnt; i++) {
if (insn_state[i] != EXPLORED) {
verbose("unreachable insn %d\n", i);
ret = -EINVAL;
goto err_free;
}
}
ret = 0; /* cfg looks good */
err_free:
kfree(insn_state);
kfree(insn_stack);
return ret;
}
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
/* the following conditions reduce the number of explored insns
* from ~140k to ~80k for ultra large programs that use a lot of ptr_to_packet
*/
static bool compare_ptrs_to_packet(struct reg_state *old, struct reg_state *cur)
{
if (old->id != cur->id)
return false;
/* old ptr_to_packet is more conservative, since it allows smaller
* range. Ex:
* old(off=0,r=10) is equal to cur(off=0,r=20), because
* old(off=0,r=10) means that with range=10 the verifier proceeded
* further and found no issues with the program. Now we're in the same
* spot with cur(off=0,r=20), so we're safe too, since anything further
* will only be looking at most 10 bytes after this pointer.
*/
if (old->off == cur->off && old->range < cur->range)
return true;
/* old(off=20,r=10) is equal to cur(off=22,re=22 or 5 or 0)
* since both cannot be used for packet access and safe(old)
* pointer has smaller off that could be used for further
* 'if (ptr > data_end)' check
* Ex:
* old(off=20,r=10) and cur(off=22,r=22) and cur(off=22,r=0) mean
* that we cannot access the packet.
* The safe range is:
* [ptr, ptr + range - off)
* so whenever off >=range, it means no safe bytes from this pointer.
* When comparing old->off <= cur->off, it means that older code
* went with smaller offset and that offset was later
* used to figure out the safe range after 'if (ptr > data_end)' check
* Say, 'old' state was explored like:
* ... R3(off=0, r=0)
* R4 = R3 + 20
* ... now R4(off=20,r=0) <-- here
* if (R4 > data_end)
* ... R4(off=20,r=20), R3(off=0,r=20) and R3 can be used to access.
* ... the code further went all the way to bpf_exit.
* Now the 'cur' state at the mark 'here' has R4(off=30,r=0).
* old_R4(off=20,r=0) equal to cur_R4(off=30,r=0), since if the verifier
* goes further, such cur_R4 will give larger safe packet range after
* 'if (R4 > data_end)' and all further insn were already good with r=20,
* so they will be good with r=30 and we can prune the search.
*/
if (old->off <= cur->off &&
old->off >= old->range && cur->off >= cur->range)
return true;
return false;
}
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
/* compare two verifier states
*
* all states stored in state_list are known to be valid, since
* verifier reached 'bpf_exit' instruction through them
*
* this function is called when verifier exploring different branches of
* execution popped from the state stack. If it sees an old state that has
* more strict register state and more strict stack state then this execution
* branch doesn't need to be explored further, since verifier already
* concluded that more strict state leads to valid finish.
*
* Therefore two states are equivalent if register state is more conservative
* and explored stack state is more conservative than the current one.
* Example:
* explored current
* (slot1=INV slot2=MISC) == (slot1=MISC slot2=MISC)
* (slot1=MISC slot2=MISC) != (slot1=INV slot2=MISC)
*
* In other words if current stack state (one being explored) has more
* valid slots than old one that already passed validation, it means
* the verifier can stop exploring and conclude that current state is valid too
*
* Similarly with registers. If explored state has register type as invalid
* whereas register type in current state is meaningful, it means that
* the current state will reach 'bpf_exit' instruction safely
*/
static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
{
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
struct reg_state *rold, *rcur;
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
int i;
for (i = 0; i < MAX_BPF_REG; i++) {
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
rold = &old->regs[i];
rcur = &cur->regs[i];
if (memcmp(rold, rcur, sizeof(*rold)) == 0)
continue;
if (rold->type == NOT_INIT ||
(rold->type == UNKNOWN_VALUE && rcur->type != NOT_INIT))
continue;
bpf: direct packet access Extended BPF carried over two instructions from classic to access packet data: LD_ABS and LD_IND. They're highly optimized in JITs, but due to their design they have to do length check for every access. When BPF is processing 20M packets per second single LD_ABS after JIT is consuming 3% cpu. Hence the need to optimize it further by amortizing the cost of 'off < skb_headlen' over multiple packet accesses. One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW with similar usage as skb_header_pointer(). The kernel part for interpreter and x64 JIT was implemented in [1], but such new insns behave like old ld_abs and abort the program with 'return 0' if access is beyond linear data. Such hidden control flow is hard to workaround plus changing JITs and rolling out new llvm is incovenient. Therefore allow cls_bpf/act_bpf program access skb->data directly: int bpf_prog(struct __sk_buff *skb) { struct iphdr *ip; if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end) /* packet too small */ return 0; ip = skb->data + ETH_HLEN; /* access IP header fields with direct loads */ if (ip->version != 4 || ip->saddr == 0x7f000001) return 1; [...] } This solution avoids introduction of new instructions. llvm stays the same and all JITs stay the same, but verifier has to work extra hard to prove safety of the above program. For XDP the direct store instructions can be allowed as well. The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check the alignment. The complex packet parsers where packet pointer is adjusted incrementally cannot be tracked for alignment, so allow byte access in such cases and misaligned access on architectures that define efficient_unaligned_access [1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dw Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:10 +08:00
if (rold->type == PTR_TO_PACKET && rcur->type == PTR_TO_PACKET &&
compare_ptrs_to_packet(rold, rcur))
continue;
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
return false;
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
}
for (i = 0; i < MAX_BPF_STACK; i++) {
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
if (old->stack_slot_type[i] == STACK_INVALID)
continue;
if (old->stack_slot_type[i] != cur->stack_slot_type[i])
/* Ex: old explored (safe) state has STACK_SPILL in
* this stack slot, but current has has STACK_MISC ->
* this verifier states are not equivalent,
* return false to continue verification of this path
*/
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
return false;
bpf: reduce verifier memory consumption verifier keeps track of register state spilled to stack. registers are 8-byte wide and always aligned, so instead of tracking them in every byte-sized stack slot, use MAX_BPF_STACK / 8 array to track spilled register state. Though verifier runs in user context and its state freed immediately after verification, it makes sense to reduce its memory usage. This optimization reduces sizeof(struct verifier_state) from 12464 to 1712 on 64-bit and from 6232 to 1112 on 32-bit. Note, this patch doesn't change existing limits, which are there to bound time and memory during verification: 4k total number of insns in a program, 1k number of jumps (states to visit) and 32k number of processed insn (since an insn may be visited multiple times). Theoretical worst case memory during verification is 1712 * 1k = 17Mbyte. Out-of-memory situation triggers cleanup and rejects the program. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-29 06:11:41 +08:00
if (i % BPF_REG_SIZE)
continue;
if (memcmp(&old->spilled_regs[i / BPF_REG_SIZE],
&cur->spilled_regs[i / BPF_REG_SIZE],
sizeof(old->spilled_regs[0])))
/* when explored and current stack slot types are
* the same, check that stored pointers types
* are the same as well.
* Ex: explored safe path could have stored
* (struct reg_state) {.type = PTR_TO_STACK, .imm = -8}
* but current path has stored:
* (struct reg_state) {.type = PTR_TO_STACK, .imm = -16}
* such verifier states are not equivalent.
* return false to continue verification of this path
*/
return false;
else
continue;
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
}
return true;
}
static int is_state_visited(struct verifier_env *env, int insn_idx)
{
struct verifier_state_list *new_sl;
struct verifier_state_list *sl;
sl = env->explored_states[insn_idx];
if (!sl)
/* this 'insn_idx' instruction wasn't marked, so we will not
* be doing state search here
*/
return 0;
while (sl != STATE_LIST_MARK) {
if (states_equal(&sl->state, &env->cur_state))
/* reached equivalent register/stack state,
* prune the search
*/
return 1;
sl = sl->next;
}
/* there were no equivalent states, remember current one.
* technically the current state is not proven to be safe yet,
* but it will either reach bpf_exit (which means it's safe) or
* it will be rejected. Since there are no loops, we won't be
* seeing this 'insn_idx' instruction again on the way to bpf_exit
*/
new_sl = kmalloc(sizeof(struct verifier_state_list), GFP_USER);
if (!new_sl)
return -ENOMEM;
/* add new state to the head of linked list */
memcpy(&new_sl->state, &env->cur_state, sizeof(env->cur_state));
new_sl->next = env->explored_states[insn_idx];
env->explored_states[insn_idx] = new_sl;
return 0;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
static int do_check(struct verifier_env *env)
{
struct verifier_state *state = &env->cur_state;
struct bpf_insn *insns = env->prog->insnsi;
struct reg_state *regs = state->regs;
int insn_cnt = env->prog->len;
int insn_idx, prev_insn_idx = 0;
int insn_processed = 0;
bool do_print_state = false;
init_reg_state(regs);
insn_idx = 0;
for (;;) {
struct bpf_insn *insn;
u8 class;
int err;
if (insn_idx >= insn_cnt) {
verbose("invalid insn idx %d insn_cnt %d\n",
insn_idx, insn_cnt);
return -EFAULT;
}
insn = &insns[insn_idx];
class = BPF_CLASS(insn->code);
bpf, verifier: further improve search pruning The verifier needs to go through every path of the program in order to check that it terminates safely, which can be quite a lot of instructions that need to be processed f.e. in cases with more branchy programs. With search pruning from f1bca824dabb ("bpf: add search pruning optimization to verifier") the search space can already be reduced significantly when the verifier detects that a previously walked path with same register and stack contents terminated already (see verifier's states_equal()), so the search can skip walking those states. When working with larger programs of > ~2000 (out of max 4096) insns, we found that the current limit of 32k instructions is easily hit. For example, a case we ran into is that the search space cannot be pruned due to branches at the beginning of the program that make use of certain stack space slots (STACK_MISC), which are never used in the remaining program (STACK_INVALID). Therefore, the verifier needs to walk paths for the slots in STACK_INVALID state, but also all remaining paths with a stack structure, where the slots are in STACK_MISC, which can nearly double the search space needed. After various experiments, we find that a limit of 64k processed insns is a more reasonable choice when dealing with larger programs in practice. This still allows to reject extreme crafted cases that can have a much higher complexity (f.e. > ~300k) within the 4096 insns limit due to search pruning not being able to take effect. Furthermore, we found that a lot of states can be pruned after a call instruction, f.e. we were able to reduce the search state by ~35% in some cases with this heuristic, trade-off is to keep a bit more states in env->explored_states. Usually, call instructions have a number of preceding register assignments and/or stack stores, where search pruning has a better chance to suceed in states_equal() test. The current code marks the branch targets with STATE_LIST_MARK in case of conditional jumps, and the next (t + 1) instruction in case of unconditional jump so that f.e. a backjump will walk it. We also did experiments with using t + insns[t].off + 1 as a marker in the unconditionally jump case instead of t + 1 with the rationale that these two branches of execution that converge after the label might have more potential of pruning. We found that it was a bit better, but not necessarily significantly better than the current state, perhaps also due to clang not generating back jumps often. Hence, we left that as is for now. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-06 04:33:17 +08:00
if (++insn_processed > BPF_COMPLEXITY_LIMIT_INSNS) {
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
verbose("BPF program is too large. Proccessed %d insn\n",
insn_processed);
return -E2BIG;
}
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
err = is_state_visited(env, insn_idx);
if (err < 0)
return err;
if (err == 1) {
/* found equivalent state, can prune the search */
if (log_level) {
if (do_print_state)
verbose("\nfrom %d to %d: safe\n",
prev_insn_idx, insn_idx);
else
verbose("%d: safe\n", insn_idx);
}
goto process_bpf_exit;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (log_level && do_print_state) {
verbose("\nfrom %d to %d:", prev_insn_idx, insn_idx);
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
print_verifier_state(&env->cur_state);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
do_print_state = false;
}
if (log_level) {
verbose("%d: ", insn_idx);
print_bpf_insn(insn);
}
if (class == BPF_ALU || class == BPF_ALU64) {
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
err = check_alu_op(env, insn);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (err)
return err;
} else if (class == BPF_LDX) {
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
enum bpf_reg_type src_reg_type;
/* check for reserved fields is already done */
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* check src operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
err = check_reg_arg(regs, insn->dst_reg, DST_OP_NO_MARK);
if (err)
return err;
bpf: fix two bugs in verification logic when accessing 'ctx' pointer 1. first bug is a silly mistake. It broke tracing examples and prevented simple bpf programs from loading. In the following code: if (insn->imm == 0 && BPF_SIZE(insn->code) == BPF_W) { } else if (...) { // this part should have been executed when // insn->code == BPF_W and insn->imm != 0 } Obviously it's not doing that. So simple instructions like: r2 = *(u64 *)(r1 + 8) will be rejected. Note the comments in the code around these branches were and still valid and indicate the true intent. Replace it with: if (BPF_SIZE(insn->code) != BPF_W) continue; if (insn->imm == 0) { } else if (...) { // now this code will be executed when // insn->code == BPF_W and insn->imm != 0 } 2. second bug is more subtle. If malicious code is using the same dest register as source register, the checks designed to prevent the same instruction to be used with different pointer types will fail to trigger, since we were assigning src_reg_type when it was already overwritten by check_mem_access(). The fix is trivial. Just move line: src_reg_type = regs[insn->src_reg].type; before check_mem_access(). Add new 'access skb fields bad4' test to check this case. Fixes: 9bac3d6d548e ("bpf: allow extended BPF programs access skb fields") Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-16 07:19:33 +08:00
src_reg_type = regs[insn->src_reg].type;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* check that memory (src_reg + off) is readable,
* the state of dst_reg will be updated by this func
*/
err = check_mem_access(env, insn->src_reg, insn->off,
BPF_SIZE(insn->code), BPF_READ,
insn->dst_reg);
if (err)
return err;
bpf: fix two bugs in verification logic when accessing 'ctx' pointer 1. first bug is a silly mistake. It broke tracing examples and prevented simple bpf programs from loading. In the following code: if (insn->imm == 0 && BPF_SIZE(insn->code) == BPF_W) { } else if (...) { // this part should have been executed when // insn->code == BPF_W and insn->imm != 0 } Obviously it's not doing that. So simple instructions like: r2 = *(u64 *)(r1 + 8) will be rejected. Note the comments in the code around these branches were and still valid and indicate the true intent. Replace it with: if (BPF_SIZE(insn->code) != BPF_W) continue; if (insn->imm == 0) { } else if (...) { // now this code will be executed when // insn->code == BPF_W and insn->imm != 0 } 2. second bug is more subtle. If malicious code is using the same dest register as source register, the checks designed to prevent the same instruction to be used with different pointer types will fail to trigger, since we were assigning src_reg_type when it was already overwritten by check_mem_access(). The fix is trivial. Just move line: src_reg_type = regs[insn->src_reg].type; before check_mem_access(). Add new 'access skb fields bad4' test to check this case. Fixes: 9bac3d6d548e ("bpf: allow extended BPF programs access skb fields") Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-16 07:19:33 +08:00
if (BPF_SIZE(insn->code) != BPF_W) {
insn_idx++;
continue;
}
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
bpf: fix two bugs in verification logic when accessing 'ctx' pointer 1. first bug is a silly mistake. It broke tracing examples and prevented simple bpf programs from loading. In the following code: if (insn->imm == 0 && BPF_SIZE(insn->code) == BPF_W) { } else if (...) { // this part should have been executed when // insn->code == BPF_W and insn->imm != 0 } Obviously it's not doing that. So simple instructions like: r2 = *(u64 *)(r1 + 8) will be rejected. Note the comments in the code around these branches were and still valid and indicate the true intent. Replace it with: if (BPF_SIZE(insn->code) != BPF_W) continue; if (insn->imm == 0) { } else if (...) { // now this code will be executed when // insn->code == BPF_W and insn->imm != 0 } 2. second bug is more subtle. If malicious code is using the same dest register as source register, the checks designed to prevent the same instruction to be used with different pointer types will fail to trigger, since we were assigning src_reg_type when it was already overwritten by check_mem_access(). The fix is trivial. Just move line: src_reg_type = regs[insn->src_reg].type; before check_mem_access(). Add new 'access skb fields bad4' test to check this case. Fixes: 9bac3d6d548e ("bpf: allow extended BPF programs access skb fields") Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-04-16 07:19:33 +08:00
if (insn->imm == 0) {
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
/* saw a valid insn
* dst_reg = *(u32 *)(src_reg + off)
* use reserved 'imm' field to mark this insn
*/
insn->imm = src_reg_type;
} else if (src_reg_type != insn->imm &&
(src_reg_type == PTR_TO_CTX ||
insn->imm == PTR_TO_CTX)) {
/* ABuser program is trying to use the same insn
* dst_reg = *(u32*) (src_reg + off)
* with different pointer types:
* src_reg == ctx in one branch and
* src_reg == stack|map in some other branch.
* Reject it.
*/
verbose("same insn cannot be used with different pointers\n");
return -EINVAL;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else if (class == BPF_STX) {
bpf: allow programs to write to certain skb fields allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-06-05 01:11:54 +08:00
enum bpf_reg_type dst_reg_type;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
if (BPF_MODE(insn->code) == BPF_XADD) {
err = check_xadd(env, insn);
if (err)
return err;
insn_idx++;
continue;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
return err;
/* check src2 operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
bpf: allow programs to write to certain skb fields allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-06-05 01:11:54 +08:00
dst_reg_type = regs[insn->dst_reg].type;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
insn->src_reg);
if (err)
return err;
bpf: allow programs to write to certain skb fields allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-06-05 01:11:54 +08:00
if (insn->imm == 0) {
insn->imm = dst_reg_type;
} else if (dst_reg_type != insn->imm &&
(dst_reg_type == PTR_TO_CTX ||
insn->imm == PTR_TO_CTX)) {
verbose("same insn cannot be used with different pointers\n");
return -EINVAL;
}
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else if (class == BPF_ST) {
if (BPF_MODE(insn->code) != BPF_MEM ||
insn->src_reg != BPF_REG_0) {
verbose("BPF_ST uses reserved fields\n");
return -EINVAL;
}
/* check src operand */
err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
if (err)
return err;
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
-1);
if (err)
return err;
} else if (class == BPF_JMP) {
u8 opcode = BPF_OP(insn->code);
if (opcode == BPF_CALL) {
if (BPF_SRC(insn->code) != BPF_K ||
insn->off != 0 ||
insn->src_reg != BPF_REG_0 ||
insn->dst_reg != BPF_REG_0) {
verbose("BPF_CALL uses reserved fields\n");
return -EINVAL;
}
err = check_call(env, insn->imm);
if (err)
return err;
} else if (opcode == BPF_JA) {
if (BPF_SRC(insn->code) != BPF_K ||
insn->imm != 0 ||
insn->src_reg != BPF_REG_0 ||
insn->dst_reg != BPF_REG_0) {
verbose("BPF_JA uses reserved fields\n");
return -EINVAL;
}
insn_idx += insn->off + 1;
continue;
} else if (opcode == BPF_EXIT) {
if (BPF_SRC(insn->code) != BPF_K ||
insn->imm != 0 ||
insn->src_reg != BPF_REG_0 ||
insn->dst_reg != BPF_REG_0) {
verbose("BPF_EXIT uses reserved fields\n");
return -EINVAL;
}
/* eBPF calling convetion is such that R0 is used
* to return the value from eBPF program.
* Make sure that it's readable at this time
* of bpf_exit, which means that program wrote
* something into it earlier
*/
err = check_reg_arg(regs, BPF_REG_0, SRC_OP);
if (err)
return err;
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
if (is_pointer_value(env, BPF_REG_0)) {
verbose("R0 leaks addr as return value\n");
return -EACCES;
}
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
process_bpf_exit:
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
insn_idx = pop_stack(env, &prev_insn_idx);
if (insn_idx < 0) {
break;
} else {
do_print_state = true;
continue;
}
} else {
err = check_cond_jmp_op(env, insn, &insn_idx);
if (err)
return err;
}
} else if (class == BPF_LD) {
u8 mode = BPF_MODE(insn->code);
if (mode == BPF_ABS || mode == BPF_IND) {
bpf: verifier: add checks for BPF_ABS | BPF_IND instructions introduce program type BPF_PROG_TYPE_SOCKET_FILTER that is used for attaching programs to sockets where ctx == skb. add verifier checks for ABS/IND instructions which can only be seen in socket filters, therefore the check: if (env->prog->aux->prog_type != BPF_PROG_TYPE_SOCKET_FILTER) verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n"); Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-02 07:06:34 +08:00
err = check_ld_abs(env, insn);
if (err)
return err;
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
} else if (mode == BPF_IMM) {
err = check_ld_imm(env, insn);
if (err)
return err;
insn_idx++;
} else {
verbose("invalid BPF_LD mode\n");
return -EINVAL;
}
} else {
verbose("unknown insn class %d\n", class);
return -EINVAL;
}
insn_idx++;
}
bpf: cleanup verifier code cleanup verifier code and prepare it for addition of "pointer to packet" logic Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-06 10:49:09 +08:00
verbose("processed %d insns\n", insn_processed);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
return 0;
}
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
/* look for pseudo eBPF instructions that access map FDs and
* replace them with actual map pointers
*/
static int replace_map_fd_with_map_ptr(struct verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
int i, j;
for (i = 0; i < insn_cnt; i++, insn++) {
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
if (BPF_CLASS(insn->code) == BPF_LDX &&
bpf: allow programs to write to certain skb fields allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-06-05 01:11:54 +08:00
(BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
verbose("BPF_LDX uses reserved fields\n");
return -EINVAL;
}
bpf: allow programs to write to certain skb fields allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-06-05 01:11:54 +08:00
if (BPF_CLASS(insn->code) == BPF_STX &&
((BPF_MODE(insn->code) != BPF_MEM &&
BPF_MODE(insn->code) != BPF_XADD) || insn->imm != 0)) {
verbose("BPF_STX uses reserved fields\n");
return -EINVAL;
}
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
struct bpf_map *map;
struct fd f;
if (i == insn_cnt - 1 || insn[1].code != 0 ||
insn[1].dst_reg != 0 || insn[1].src_reg != 0 ||
insn[1].off != 0) {
verbose("invalid bpf_ld_imm64 insn\n");
return -EINVAL;
}
if (insn->src_reg == 0)
/* valid generic load 64-bit imm */
goto next_insn;
if (insn->src_reg != BPF_PSEUDO_MAP_FD) {
verbose("unrecognized bpf_ld_imm64 insn\n");
return -EINVAL;
}
f = fdget(insn->imm);
bpf: align and clean bpf_{map,prog}_get helpers Add a bpf_map_get() function that we're going to use later on and align/clean the remaining helpers a bit so that we have them a bit more consistent: - __bpf_map_get() and __bpf_prog_get() that both work on the fd struct, check whether the descriptor is eBPF and return the pointer to the map/prog stored in the private data. Also, we can return f.file->private_data directly, the function signature is enough of a documentation already. - bpf_map_get() and bpf_prog_get() that both work on u32 user fd, call their respective __bpf_map_get()/__bpf_prog_get() variants, and take a reference. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-29 21:58:07 +08:00
map = __bpf_map_get(f);
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
if (IS_ERR(map)) {
verbose("fd %d is not pointing to valid bpf_map\n",
insn->imm);
return PTR_ERR(map);
}
/* store map pointer inside BPF_LD_IMM64 instruction */
insn[0].imm = (u32) (unsigned long) map;
insn[1].imm = ((u64) (unsigned long) map) >> 32;
/* check whether we recorded this map already */
for (j = 0; j < env->used_map_cnt; j++)
if (env->used_maps[j] == map) {
fdput(f);
goto next_insn;
}
if (env->used_map_cnt >= MAX_USED_MAPS) {
fdput(f);
return -E2BIG;
}
/* hold the map. If the program is rejected by verifier,
* the map will be released by release_maps() or it
* will be used by the valid program until it's unloaded
* and all maps are released in free_bpf_prog_info()
*/
bpf: fix refcnt overflow On a system with >32Gbyte of phyiscal memory and infinite RLIMIT_MEMLOCK, the malicious application may overflow 32-bit bpf program refcnt. It's also possible to overflow map refcnt on 1Tb system. Impose 32k hard limit which means that the same bpf program or map cannot be shared by more than 32k processes. Fixes: 1be7f75d1668 ("bpf: enable non-root eBPF programs") Reported-by: Jann Horn <jannh@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-28 09:56:20 +08:00
map = bpf_map_inc(map, false);
if (IS_ERR(map)) {
fdput(f);
return PTR_ERR(map);
}
env->used_maps[env->used_map_cnt++] = map;
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
fdput(f);
next_insn:
insn++;
i++;
}
}
/* now all pseudo BPF_LD_IMM64 instructions load valid
* 'struct bpf_map *' into a register instead of user map_fd.
* These pointers will be used later by verifier to validate map access.
*/
return 0;
}
/* drop refcnt of maps used by the rejected program */
static void release_maps(struct verifier_env *env)
{
int i;
for (i = 0; i < env->used_map_cnt; i++)
bpf_map_put(env->used_maps[i]);
}
/* convert pseudo BPF_LD_IMM64 into generic BPF_LD_IMM64 */
static void convert_pseudo_ld_imm64(struct verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
int i;
for (i = 0; i < insn_cnt; i++, insn++)
if (insn->code == (BPF_LD | BPF_IMM | BPF_DW))
insn->src_reg = 0;
}
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
/* convert load instructions that access fields of 'struct __sk_buff'
* into sequence of instructions that access fields of 'struct sk_buff'
*/
static int convert_ctx_accesses(struct verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
struct bpf_insn insn_buf[16];
struct bpf_prog *new_prog;
bpf: allow programs to write to certain skb fields allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-06-05 01:11:54 +08:00
enum bpf_access_type type;
bpf: add bpf_patch_insn_single helper Move the functionality to patch instructions out of the verifier code and into the core as the new bpf_patch_insn_single() helper will be needed later on for blinding as well. No changes in functionality. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-14 01:08:30 +08:00
int i;
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
if (!env->prog->aux->ops->convert_ctx_access)
return 0;
for (i = 0; i < insn_cnt; i++, insn++) {
bpf: add bpf_patch_insn_single helper Move the functionality to patch instructions out of the verifier code and into the core as the new bpf_patch_insn_single() helper will be needed later on for blinding as well. No changes in functionality. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-14 01:08:30 +08:00
u32 insn_delta, cnt;
bpf: allow programs to write to certain skb fields allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-06-05 01:11:54 +08:00
if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
type = BPF_READ;
else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
type = BPF_WRITE;
else
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
continue;
if (insn->imm != PTR_TO_CTX) {
/* clear internal mark */
insn->imm = 0;
continue;
}
cnt = env->prog->aux->ops->
bpf: allow programs to write to certain skb fields allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-06-05 01:11:54 +08:00
convert_ctx_access(type, insn->dst_reg, insn->src_reg,
bpf: fix cb access in socket filter programs eBPF socket filter programs may see junk in 'u32 cb[5]' area, since it could have been used by protocol layers earlier. For socket filter programs used in af_packet we need to clean 20 bytes of skb->cb area if it could be used by the program. For programs attached to TCP/UDP sockets we need to save/restore these 20 bytes, since it's used by protocol layers. Remove SK_RUN_FILTER macro, since it's no longer used. Long term we may move this bpf cb area to per-cpu scratch, but that requires addition of new 'per-cpu load/store' instructions, so not suitable as a short term fix. Fixes: d691f9e8d440 ("bpf: allow programs to write to certain skb fields") Reported-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 01:55:41 +08:00
insn->off, insn_buf, env->prog);
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
verbose("bpf verifier is misconfigured\n");
return -EINVAL;
}
bpf: add bpf_patch_insn_single helper Move the functionality to patch instructions out of the verifier code and into the core as the new bpf_patch_insn_single() helper will be needed later on for blinding as well. No changes in functionality. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-14 01:08:30 +08:00
new_prog = bpf_patch_insn_single(env->prog, i, insn_buf, cnt);
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
if (!new_prog)
return -ENOMEM;
bpf: add bpf_patch_insn_single helper Move the functionality to patch instructions out of the verifier code and into the core as the new bpf_patch_insn_single() helper will be needed later on for blinding as well. No changes in functionality. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-14 01:08:30 +08:00
insn_delta = cnt - 1;
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
/* keep walking new program and skip insns we just inserted */
env->prog = new_prog;
bpf: add bpf_patch_insn_single helper Move the functionality to patch instructions out of the verifier code and into the core as the new bpf_patch_insn_single() helper will be needed later on for blinding as well. No changes in functionality. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-14 01:08:30 +08:00
insn = new_prog->insnsi + i + insn_delta;
insn_cnt += insn_delta;
i += insn_delta;
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
}
return 0;
}
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
static void free_states(struct verifier_env *env)
{
struct verifier_state_list *sl, *sln;
int i;
if (!env->explored_states)
return;
for (i = 0; i < env->prog->len; i++) {
sl = env->explored_states[i];
if (sl)
while (sl != STATE_LIST_MARK) {
sln = sl->next;
kfree(sl);
sl = sln;
}
}
kfree(env->explored_states);
}
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
bpf: verifier (add docs) this patch adds all of eBPF verfier documentation and empty bpf_check() The end goal for the verifier is to statically check safety of the program. Verifier will catch: - loops - out of range jumps - unreachable instructions - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention More details in Documentation/networking/filter.txt Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:02 +08:00
{
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
char __user *log_ubuf = NULL;
struct verifier_env *env;
bpf: verifier (add docs) this patch adds all of eBPF verfier documentation and empty bpf_check() The end goal for the verifier is to statically check safety of the program. Verifier will catch: - loops - out of range jumps - unreachable instructions - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention More details in Documentation/networking/filter.txt Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:02 +08:00
int ret = -EINVAL;
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
if ((*prog)->len <= 0 || (*prog)->len > BPF_MAXINSNS)
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
return -E2BIG;
/* 'struct verifier_env' can be global, but since it's not small,
* allocate/free it every time bpf_check() is called
*/
env = kzalloc(sizeof(struct verifier_env), GFP_KERNEL);
if (!env)
return -ENOMEM;
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
env->prog = *prog;
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
/* grab the mutex to protect few globals used by verifier */
mutex_lock(&bpf_verifier_lock);
if (attr->log_level || attr->log_buf || attr->log_size) {
/* user requested verbose verifier output
* and supplied buffer to store the verification trace
*/
log_level = attr->log_level;
log_ubuf = (char __user *) (unsigned long) attr->log_buf;
log_size = attr->log_size;
log_len = 0;
ret = -EINVAL;
/* log_* values have to be sane */
if (log_size < 128 || log_size > UINT_MAX >> 8 ||
log_level == 0 || log_ubuf == NULL)
goto free_env;
ret = -ENOMEM;
log_buf = vmalloc(log_size);
if (!log_buf)
goto free_env;
} else {
log_level = 0;
}
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
ret = replace_map_fd_with_map_ptr(env);
if (ret < 0)
goto skip_full_check;
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
env->explored_states = kcalloc(env->prog->len,
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
sizeof(struct verifier_state_list *),
GFP_USER);
ret = -ENOMEM;
if (!env->explored_states)
goto skip_full_check;
bpf: verifier (add branch/goto checks) check that control flow graph of eBPF program is a directed acyclic graph check_cfg() does: - detect loops - detect unreachable instructions - check that program terminates with BPF_EXIT insn - check that all branches are within program boundary Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:05 +08:00
ret = check_cfg(env);
if (ret < 0)
goto skip_full_check;
bpf: enable non-root eBPF programs In order to let unprivileged users load and execute eBPF programs teach verifier to prevent pointer leaks. Verifier will prevent - any arithmetic on pointers (except R10+Imm which is used to compute stack addresses) - comparison of pointers (except if (map_value_ptr == 0) ... ) - passing pointers to helper functions - indirectly passing pointers in stack to helper functions - returning pointer from bpf program - storing pointers into ctx or maps Spill/fill of pointers into stack is allowed, but mangling of pointers stored in the stack or reading them byte by byte is not. Within bpf programs the pointers do exist, since programs need to be able to access maps, pass skb pointer to LD_ABS insns, etc but programs cannot pass such pointer values to the outside or obfuscate them. Only allow BPF_PROG_TYPE_SOCKET_FILTER unprivileged programs, so that socket filters (tcpdump), af_packet (quic acceleration) and future kcm can use it. tracing and tc cls/act program types still require root permissions, since tracing actually needs to be able to see all kernel pointers and tc is for root only. For example, the following unprivileged socket filter program is allowed: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += skb->len; return 0; } but the following program is not: int bpf_prog1(struct __sk_buff *skb) { u32 index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); u64 *value = bpf_map_lookup_elem(&my_map, &index); if (value) *value += (u64) skb; return 0; } since it would leak the kernel address into the map. Unprivileged socket filter bpf programs have access to the following helper functions: - map lookup/update/delete (but they cannot store kernel pointers into them) - get_random (it's already exposed to unprivileged user space) - get_smp_processor_id - tail_call into another socket filter program - ktime_get_ns The feature is controlled by sysctl kernel.unprivileged_bpf_disabled. This toggle defaults to off (0), but can be set true (1). Once true, bpf programs and maps cannot be accessed from unprivileged process, and the toggle cannot be set back to false. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-08 13:23:21 +08:00
env->allow_ptr_leaks = capable(CAP_SYS_ADMIN);
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
ret = do_check(env);
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
skip_full_check:
bpf: verifier (add verifier core) This patch adds verifier core which simulates execution of every insn and records the state of registers and program stack. Every branch instruction seen during simulation is pushed into state stack. When verifier reaches BPF_EXIT, it pops the state from the stack and continues until it reaches BPF_EXIT again. For program: 1: bpf_mov r1, xxx 2: if (r1 == 0) goto 5 3: bpf_mov r0, 1 4: goto 6 5: bpf_mov r0, 2 6: bpf_exit The verifier will walk insns: 1, 2, 3, 4, 6 then it will pop the state recorded at insn#2 and will continue: 5, 6 This way it walks all possible paths through the program and checks all possible values of registers. While doing so, it checks for: - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention - instruction encoding is not using reserved fields Kernel subsystem configures the verifier with two callbacks: - bool (*is_valid_access)(int off, int size, enum bpf_access_type type); that provides information to the verifer which fields of 'ctx' are accessible (remember 'ctx' is the first argument to eBPF program) - const struct bpf_func_proto *(*get_func_proto)(enum bpf_func_id func_id); returns argument constraints of kernel helper functions that eBPF program may call, so that verifier can checks that R1-R5 types match the prototype More details in Documentation/networking/filter.txt and in kernel/bpf/verifier.c Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:06 +08:00
while (pop_stack(env, NULL) >= 0);
bpf: add search pruning optimization to verifier consider C program represented in eBPF: int filter(int arg) { int a, b, c, *ptr; if (arg == 1) ptr = &a; else if (arg == 2) ptr = &b; else ptr = &c; *ptr = 0; return 0; } eBPF verifier has to follow all possible paths through the program to recognize that '*ptr = 0' instruction would be safe to execute in all situations. It's doing it by picking a path towards the end and observes changes to registers and stack at every insn until it reaches bpf_exit. Then it comes back to one of the previous branches and goes towards the end again with potentially different values in registers. When program has a lot of branches, the number of possible combinations of branches is huge, so verifer has a hard limit of walking no more than 32k instructions. This limit can be reached and complex (but valid) programs could be rejected. Therefore it's important to recognize equivalent verifier states to prune this depth first search. Basic idea can be illustrated by the program (where .. are some eBPF insns): 1: .. 2: if (rX == rY) goto 4 3: .. 4: .. 5: .. 6: bpf_exit In the first pass towards bpf_exit the verifier will walk insns: 1, 2, 3, 4, 5, 6 Since insn#2 is a branch the verifier will remember its state in verifier stack to come back to it later. Since insn#4 is marked as 'branch target', the verifier will remember its state in explored_states[4] linked list. Once it reaches insn#6 successfully it will pop the state recorded at insn#2 and will continue. Without search pruning optimization verifier would have to walk 4, 5, 6 again, effectively simulating execution of insns 1, 2, 4, 5, 6 With search pruning it will check whether state at #4 after jumping from #2 is equivalent to one recorded in explored_states[4] during first pass. If there is an equivalent state, verifier can prune the search at #4 and declare this path to be safe as well. In other words two states at #4 are equivalent if execution of 1, 2, 3, 4 insns and 1, 2, 4 insns produces equivalent registers and stack. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-30 09:50:01 +08:00
free_states(env);
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
if (ret == 0)
/* program is valid, convert *(u32*)(ctx + off) accesses */
ret = convert_ctx_accesses(env);
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
if (log_level && log_len >= log_size - 1) {
BUG_ON(log_len >= log_size);
/* verifier log exceeded user supplied buffer */
ret = -ENOSPC;
/* fall through to return what was recorded */
}
/* copy verifier log back to user space including trailing zero */
if (log_level && copy_to_user(log_ubuf, log_buf, log_len + 1) != 0) {
ret = -EFAULT;
goto free_log_buf;
}
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
if (ret == 0 && env->used_map_cnt) {
/* if program passed verifier, update used_maps in bpf_prog_info */
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
env->prog->aux->used_maps = kmalloc_array(env->used_map_cnt,
sizeof(env->used_maps[0]),
GFP_KERNEL);
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
if (!env->prog->aux->used_maps) {
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
ret = -ENOMEM;
goto free_log_buf;
}
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
memcpy(env->prog->aux->used_maps, env->used_maps,
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
sizeof(env->used_maps[0]) * env->used_map_cnt);
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
env->prog->aux->used_map_cnt = env->used_map_cnt;
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
/* program is valid. Convert pseudo bpf_ld_imm64 into generic
* bpf_ld_imm64 instructions
*/
convert_pseudo_ld_imm64(env);
}
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
free_log_buf:
if (log_level)
vfree(log_buf);
free_env:
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
if (!env->prog->aux->used_maps)
bpf: handle pseudo BPF_LD_IMM64 insn eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions to refer to process-local map_fd. Scan the program for such instructions and if FDs are valid, convert them to 'struct bpf_map' pointers which will be used by verifier to check access to maps in bpf_map_lookup/update() calls. If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping BPF_PSEUDO_MAP_FD flag. Note that eBPF interpreter is generic and knows nothing about pseudo insns. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:04 +08:00
/* if we didn't copy map pointers into bpf_prog_info, release
* them now. Otherwise free_bpf_prog_info() will release them.
*/
release_maps(env);
bpf: allow extended BPF programs access skb fields introduce user accessible mirror of in-kernel 'struct sk_buff': struct __sk_buff { __u32 len; __u32 pkt_type; __u32 mark; __u32 queue_mapping; }; bpf programs can do: int bpf_prog(struct __sk_buff *skb) { __u32 var = skb->pkt_type; which will be compiled to bpf assembler as: dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type) bpf verifier will check validity of access and will convert it to: dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset)) dst_reg &= 7 since skb->pkt_type is a bitfield. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-14 02:57:42 +08:00
*prog = env->prog;
bpf: verifier (add ability to receive verification log) add optional attributes for BPF_PROG_LOAD syscall: union bpf_attr { struct { ... __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *buffer' */ }; }; when log_level > 0 the verifier will return its verification log in the user supplied buffer 'log_buf' which can be used by program author to analyze why verifier rejected given program. 'Understanding eBPF verifier messages' section of Documentation/networking/filter.txt provides several examples of these messages, like the program: BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), BPF_LD_MAP_FD(BPF_REG_1, 0), BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), BPF_EXIT_INSN(), will be rejected with the following multi-line message in log_buf: 0: (7a) *(u64 *)(r10 -8) = 0 1: (bf) r2 = r10 2: (07) r2 += -8 3: (b7) r1 = 0 4: (85) call 1 5: (15) if r0 == 0x0 goto pc+1 R0=map_ptr R10=fp 6: (7a) *(u64 *)(r0 +4) = 0 misaligned access off 4 size 8 The format of the output can change at any time as verifier evolves. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:03 +08:00
kfree(env);
mutex_unlock(&bpf_verifier_lock);
bpf: verifier (add docs) this patch adds all of eBPF verfier documentation and empty bpf_check() The end goal for the verifier is to statically check safety of the program. Verifier will catch: - loops - out of range jumps - unreachable instructions - invalid instructions - uninitialized register access - uninitialized stack access - misaligned stack access - out of range stack access - invalid calling convention More details in Documentation/networking/filter.txt Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-26 15:17:02 +08:00
return ret;
}