Commit 31fd85816d ("bpf: permits narrower load from bpf program
context fields") made the verifier add AND instructions to clear the
unwanted bits with a mask when doing a narrow load. The mask is
computed with
(1 << size * 8) - 1
where "size" is the size of the narrow load. When doing a 4 byte load
of a an 8 byte field the verifier shifts the literal 1 by 32 places to
the left. This results in an overflow of a signed integer, which is an
undefined behavior. Typically, the computed mask was zero, so the
result of the narrow load ended up being zero too.
Cast the literal to long long to avoid overflows. Note that narrow
load of the 4 byte fields does not have the undefined behavior,
because the load size can only be either 1 or 2 bytes, so shifting 1
by 8 or 16 places will not overflow it. And reading 4 bytes would not
be a narrow load of a 4 bytes field.
Fixes: 31fd85816d ("bpf: permits narrower load from bpf program context fields")
Reviewed-by: Alban Crequy <alban@kinvolk.io>
Reviewed-by: Iago López Galeiras <iago@kinvolk.io>
Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
Cc: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
After allowing a bpf prog to
- directly read the skb->sk ptr
- get the fullsock bpf_sock by "bpf_sk_fullsock()"
- get the bpf_tcp_sock by "bpf_tcp_sock()"
- get the listener sock by "bpf_get_listener_sock()"
- avoid duplicating the fields of "(bpf_)sock" and "(bpf_)tcp_sock"
into different bpf running context.
this patch is another effort to make bpf's network programming
more intuitive to do (together with memory and performance benefit).
When bpf prog needs to store data for a sk, the current practice is to
define a map with the usual 4-tuples (src/dst ip/port) as the key.
If multiple bpf progs require to store different sk data, multiple maps
have to be defined. Hence, wasting memory to store the duplicated
keys (i.e. 4 tuples here) in each of the bpf map.
[ The smallest key could be the sk pointer itself which requires
some enhancement in the verifier and it is a separate topic. ]
Also, the bpf prog needs to clean up the elem when sk is freed.
Otherwise, the bpf map will become full and un-usable quickly.
The sk-free tracking currently could be done during sk state
transition (e.g. BPF_SOCK_OPS_STATE_CB).
The size of the map needs to be predefined which then usually ended-up
with an over-provisioned map in production. Even the map was re-sizable,
while the sk naturally come and go away already, this potential re-size
operation is arguably redundant if the data can be directly connected
to the sk itself instead of proxy-ing through a bpf map.
This patch introduces sk->sk_bpf_storage to provide local storage space
at sk for bpf prog to use. The space will be allocated when the first bpf
prog has created data for this particular sk.
The design optimizes the bpf prog's lookup (and then optionally followed by
an inline update). bpf_spin_lock should be used if the inline update needs
to be protected.
BPF_MAP_TYPE_SK_STORAGE:
-----------------------
To define a bpf "sk-local-storage", a BPF_MAP_TYPE_SK_STORAGE map (new in
this patch) needs to be created. Multiple BPF_MAP_TYPE_SK_STORAGE maps can
be created to fit different bpf progs' needs. The map enforces
BTF to allow printing the sk-local-storage during a system-wise
sk dump (e.g. "ss -ta") in the future.
The purpose of a BPF_MAP_TYPE_SK_STORAGE map is not for lookup/update/delete
a "sk-local-storage" data from a particular sk.
Think of the map as a meta-data (or "type") of a "sk-local-storage". This
particular "type" of "sk-local-storage" data can then be stored in any sk.
The main purposes of this map are mostly:
1. Define the size of a "sk-local-storage" type.
2. Provide a similar syscall userspace API as the map (e.g. lookup/update,
map-id, map-btf...etc.)
3. Keep track of all sk's storages of this "type" and clean them up
when the map is freed.
sk->sk_bpf_storage:
------------------
The main lookup/update/delete is done on sk->sk_bpf_storage (which
is a "struct bpf_sk_storage"). When doing a lookup,
the "map" pointer is now used as the "key" to search on the
sk_storage->list. The "map" pointer is actually serving
as the "type" of the "sk-local-storage" that is being
requested.
To allow very fast lookup, it should be as fast as looking up an
array at a stable-offset. At the same time, it is not ideal to
set a hard limit on the number of sk-local-storage "type" that the
system can have. Hence, this patch takes a cache approach.
The last search result from sk_storage->list is cached in
sk_storage->cache[] which is a stable sized array. Each
"sk-local-storage" type has a stable offset to the cache[] array.
In the future, a map's flag could be introduced to do cache
opt-out/enforcement if it became necessary.
The cache size is 16 (i.e. 16 types of "sk-local-storage").
Programs can share map. On the program side, having a few bpf_progs
running in the networking hotpath is already a lot. The bpf_prog
should have already consolidated the existing sock-key-ed map usage
to minimize the map lookup penalty. 16 has enough runway to grow.
All sk-local-storage data will be removed from sk->sk_bpf_storage
during sk destruction.
bpf_sk_storage_get() and bpf_sk_storage_delete():
------------------------------------------------
Instead of using bpf_map_(lookup|update|delete)_elem(),
the bpf prog needs to use the new helper bpf_sk_storage_get() and
bpf_sk_storage_delete(). The verifier can then enforce the
ARG_PTR_TO_SOCKET argument. The bpf_sk_storage_get() also allows to
"create" new elem if one does not exist in the sk. It is done by
the new BPF_SK_STORAGE_GET_F_CREATE flag. An optional value can also be
provided as the initial value during BPF_SK_STORAGE_GET_F_CREATE.
The BPF_MAP_TYPE_SK_STORAGE also supports bpf_spin_lock. Together,
it has eliminated the potential use cases for an equivalent
bpf_map_update_elem() API (for bpf_prog) in this patch.
Misc notes:
----------
1. map_get_next_key is not supported. From the userspace syscall
perspective, the map has the socket fd as the key while the map
can be shared by pinned-file or map-id.
Since btf is enforced, the existing "ss" could be enhanced to pretty
print the local-storage.
Supporting a kernel defined btf with 4 tuples as the return key could
be explored later also.
2. The sk->sk_lock cannot be acquired. Atomic operations is used instead.
e.g. cmpxchg is done on the sk->sk_bpf_storage ptr.
Please refer to the source code comments for the details in
synchronization cases and considerations.
3. The mem is charged to the sk->sk_omem_alloc as the sk filter does.
Benchmark:
---------
Here is the benchmark data collected by turning on
the "kernel.bpf_stats_enabled" sysctl.
Two bpf progs are tested:
One bpf prog with the usual bpf hashmap (max_entries = 8192) with the
sk ptr as the key. (verifier is modified to support sk ptr as the key
That should have shortened the key lookup time.)
Another bpf prog is with the new BPF_MAP_TYPE_SK_STORAGE.
Both are storing a "u32 cnt", do a lookup on "egress_skb/cgroup" for
each egress skb and then bump the cnt. netperf is used to drive
data with 4096 connected UDP sockets.
BPF_MAP_TYPE_HASH with a modifier verifier (152ns per bpf run)
27: cgroup_skb name egress_sk_map tag 74f56e832918070b run_time_ns 58280107540 run_cnt 381347633
loaded_at 2019-04-15T13:46:39-0700 uid 0
xlated 344B jited 258B memlock 4096B map_ids 16
btf_id 5
BPF_MAP_TYPE_SK_STORAGE in this patch (66ns per bpf run)
30: cgroup_skb name egress_sk_stora tag d4aa70984cc7bbf6 run_time_ns 25617093319 run_cnt 390989739
loaded_at 2019-04-15T13:47:54-0700 uid 0
xlated 168B jited 156B memlock 4096B map_ids 17
btf_id 6
Here is a high-level picture on how are the objects organized:
sk
┌──────┐
│ │
│ │
│ │
│*sk_bpf_storage─────▶ bpf_sk_storage
└──────┘ ┌───────┐
┌───────────┤ list │
│ │ │
│ │ │
│ │ │
│ └───────┘
│
│ elem
│ ┌────────┐
├─▶│ snode │
│ ├────────┤
│ │ data │ bpf_map
│ ├────────┤ ┌─────────┐
│ │map_node│◀─┬─────┤ list │
│ └────────┘ │ │ │
│ │ │ │
│ elem │ │ │
│ ┌────────┐ │ └─────────┘
└─▶│ snode │ │
├────────┤ │
bpf_map │ data │ │
┌─────────┐ ├────────┤ │
│ list ├───────▶│map_node│ │
│ │ └────────┘ │
│ │ │
│ │ elem │
└─────────┘ ┌────────┐ │
┌─▶│ snode │ │
│ ├────────┤ │
│ │ data │ │
│ ├────────┤ │
│ │map_node│◀─┘
│ └────────┘
│
│
│ ┌───────┐
sk └──────────│ list │
┌──────┐ │ │
│ │ │ │
│ │ │ │
│ │ └───────┘
│*sk_bpf_storage───────▶bpf_sk_storage
└──────┘
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This is an opt-in interface that allows a tracepoint to provide a safe
buffer that can be written from a BPF_PROG_TYPE_RAW_TRACEPOINT program.
The size of the buffer must be a compile-time constant, and is checked
before allowing a BPF program to attach to a tracepoint that uses this
feature.
The pointer to this buffer will be the first argument of tracepoints
that opt in; the pointer is valid and can be bpf_probe_read() by both
BPF_PROG_TYPE_RAW_TRACEPOINT and BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE
programs that attach to such a tracepoint, but the buffer to which it
points may only be written by the latter.
Signed-off-by: Matt Mullins <mmullins@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
In case of a null check on a pointer inside a subprog, we should mark all
registers with this pointer as either safe or unknown, in both the current
and previous frames. Currently, only spilled registers and registers in
the current frame are marked. Packet bound checks in subprogs have the
same issue. This patch fixes it to mark registers in previous frames as
well.
A good reproducer for null checks looks as follow:
1: ptr = bpf_map_lookup_elem(map, &key);
2: ret = subprog(ptr) {
3: return ptr != NULL;
4: }
5: if (ret)
6: value = *ptr;
With the above, the verifier will complain on line 6 because it sees ptr
as map_value_or_null despite the null check in subprog 1.
Note that this patch fixes another resulting bug when using
bpf_sk_release():
1: sk = bpf_sk_lookup_tcp(...);
2: subprog(sk) {
3: if (sk)
4: bpf_sk_release(sk);
5: }
6: if (!sk)
7: return 0;
8: return 1;
In the above, mark_ptr_or_null_regs will warn on line 6 because it will
try to free the reference state, even though it was already freed on
line 3.
Fixes: f4d7e40a5b ("bpf: introduce function calls (verification)")
Signed-off-by: Paul Chaignon <paul.chaignon@orange.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Drop bpf_verifier_lock for root to avoid being DoS-ed by unprivileged.
The BPF verifier is now fully parallel.
All unpriv users are still serialized by bpf_verifier_lock to avoid
exhausting kernel memory by running N parallel verifications.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Move three global variables protected by bpf_verifier_lock into
'struct bpf_verifier_env' to allow parallel verification.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
verifier.c uses BPF_CAST_CALL for casting bpf call except at one
place in jit_subprogs(). Let's use the macro for consistency.
Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
There are a few "regs[regno]" here are there across "check_reg_arg", this
patch factor it out into a simple "reg" pointer. The intention is to
simplify code indentation and make the later patches in this set look
cleaner.
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
After code refactor in previous patches, the propagation logic inside the
for loop in "propagate_liveness" becomes clear that they are good enough to
be factored out into a common function "propagate_liveness_reg".
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Access to reg states were not factored out, the consequence is long code
for dereferencing them which made the indentation not good for reading.
This patch factor out these code so the core code in the loop could be
easier to follow.
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Propagation for register and stack slot are finished in separate for loop,
while they are perfect to be put into a single loop.
This could also let them share some common variables in later patches.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Currently the way to pass result from BPF helper to BPF program is to
provide memory area defined by pointer and size: func(void *, size_t).
It works great for generic use-case, but for simple types, such as int,
it's overkill and consumes two arguments when it could use just one.
Introduce new argument types ARG_PTR_TO_INT and ARG_PTR_TO_LONG to be
able to pass result from helper to program via pointer to int and long
correspondingly: func(int *) or func(long *).
New argument types are similar to ARG_PTR_TO_MEM with the following
differences:
* they don't require corresponding ARG_CONST_SIZE argument, predefined
access sizes are used instead (32bit for int, 64bit for long);
* it's possible to use more than one such an argument in a helper;
* provided pointers have to be aligned.
It's easy to introduce similar ARG_PTR_TO_CHAR and ARG_PTR_TO_SHORT
argument types. It's not done due to lack of use-case though.
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Containerized applications may run as root and it may create problems
for whole host. Specifically such applications may change a sysctl and
affect applications in other containers.
Furthermore in existing infrastructure it may not be possible to just
completely disable writing to sysctl, instead such a process should be
gradual with ability to log what sysctl are being changed by a
container, investigate, limit the set of writable sysctl to currently
used ones (so that new ones can not be changed) and eventually reduce
this set to zero.
The patch introduces new program type BPF_PROG_TYPE_CGROUP_SYSCTL and
attach type BPF_CGROUP_SYSCTL to solve these problems on cgroup basis.
New program type has access to following minimal context:
struct bpf_sysctl {
__u32 write;
};
Where @write indicates whether sysctl is being read (= 0) or written (=
1).
Helpers to access sysctl name and value will be introduced separately.
BPF_CGROUP_SYSCTL attach point is added to sysctl code right before
passing control to ctl_table->proc_handler so that BPF program can
either allow or deny access to sysctl.
Suggested-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Daniel Borkmann says:
====================
pull-request: bpf-next 2019-04-12
The following pull-request contains BPF updates for your *net-next* tree.
The main changes are:
1) Improve BPF verifier scalability for large programs through two
optimizations: i) remove verifier states that are not useful in pruning,
ii) stop walking parentage chain once first LIVE_READ is seen. Combined
gives approx 20x speedup. Increase limits for accepting large programs
under root, and add various stress tests, from Alexei.
2) Implement global data support in BPF. This enables static global variables
for .data, .rodata and .bss sections to be properly handled which allows
for more natural program development. This also opens up the possibility
to optimize program workflow by compiling ELFs only once and later only
rewriting section data before reload, from Daniel and with test cases and
libbpf refactoring from Joe.
3) Add config option to generate BTF type info for vmlinux as part of the
kernel build process. DWARF debug info is converted via pahole to BTF.
Latter relies on libbpf and makes use of BTF deduplication algorithm which
results in 100x savings compared to DWARF data. Resulting .BTF section is
typically about 2MB in size, from Andrii.
4) Add BPF verifier support for stack access with variable offset from
helpers and add various test cases along with it, from Andrey.
5) Extend bpf_skb_adjust_room() growth BPF helper to mark inner MAC header
so that L2 encapsulation can be used for tc tunnels, from Alan.
6) Add support for input __sk_buff context in BPF_PROG_TEST_RUN so that
users can define a subset of allowed __sk_buff fields that get fed into
the test program, from Stanislav.
7) Add bpf fs multi-dimensional array tests for BTF test suite and fix up
various UBSAN warnings in bpftool, from Yonghong.
8) Generate a pkg-config file for libbpf, from Luca.
9) Dump program's BTF id in bpftool, from Prashant.
10) libbpf fix to use smaller BPF log buffer size for AF_XDP's XDP
program, from Magnus.
11) kallsyms related fixes for the case when symbols are not present in
BPF selftests and samples, from Daniel
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
This work adds two new map creation flags BPF_F_RDONLY_PROG
and BPF_F_WRONLY_PROG in order to allow for read-only or
write-only BPF maps from a BPF program side.
Today we have BPF_F_RDONLY and BPF_F_WRONLY, but this only
applies to system call side, meaning the BPF program has full
read/write access to the map as usual while bpf(2) calls with
map fd can either only read or write into the map depending
on the flags. BPF_F_RDONLY_PROG and BPF_F_WRONLY_PROG allows
for the exact opposite such that verifier is going to reject
program loads if write into a read-only map or a read into a
write-only map is detected. For read-only map case also some
helpers are forbidden for programs that would alter the map
state such as map deletion, update, etc. As opposed to the two
BPF_F_RDONLY / BPF_F_WRONLY flags, BPF_F_RDONLY_PROG as well
as BPF_F_WRONLY_PROG really do correspond to the map lifetime.
We've enabled this generic map extension to various non-special
maps holding normal user data: array, hash, lru, lpm, local
storage, queue and stack. Further generic map types could be
followed up in future depending on use-case. Main use case
here is to forbid writes into .rodata map values from verifier
side.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This generic extension to BPF maps allows for directly loading
an address residing inside a BPF map value as a single BPF
ldimm64 instruction!
The idea is similar to what BPF_PSEUDO_MAP_FD does today, which
is a special src_reg flag for ldimm64 instruction that indicates
that inside the first part of the double insns's imm field is a
file descriptor which the verifier then replaces as a full 64bit
address of the map into both imm parts. For the newly added
BPF_PSEUDO_MAP_VALUE src_reg flag, the idea is the following:
the first part of the double insns's imm field is again a file
descriptor corresponding to the map, and the second part of the
imm field is an offset into the value. The verifier will then
replace both imm parts with an address that points into the BPF
map value at the given value offset for maps that support this
operation. Currently supported is array map with single entry.
It is possible to support more than just single map element by
reusing both 16bit off fields of the insns as a map index, so
full array map lookup could be expressed that way. It hasn't
been implemented here due to lack of concrete use case, but
could easily be done so in future in a compatible way, since
both off fields right now have to be 0 and would correctly
denote a map index 0.
The BPF_PSEUDO_MAP_VALUE is a distinct flag as otherwise with
BPF_PSEUDO_MAP_FD we could not differ offset 0 between load of
map pointer versus load of map's value at offset 0, and changing
BPF_PSEUDO_MAP_FD's encoding into off by one to differ between
regular map pointer and map value pointer would add unnecessary
complexity and increases barrier for debugability thus less
suitable. Using the second part of the imm field as an offset
into the value does /not/ come with limitations since maximum
possible value size is in u32 universe anyway.
This optimization allows for efficiently retrieving an address
to a map value memory area without having to issue a helper call
which needs to prepare registers according to calling convention,
etc, without needing the extra NULL test, and without having to
add the offset in an additional instruction to the value base
pointer. The verifier then treats the destination register as
PTR_TO_MAP_VALUE with constant reg->off from the user passed
offset from the second imm field, and guarantees that this is
within bounds of the map value. Any subsequent operations are
normally treated as typical map value handling without anything
extra needed from verification side.
The two map operations for direct value access have been added to
array map for now. In future other types could be supported as
well depending on the use case. The main use case for this commit
is to allow for BPF loader support for global variables that
reside in .data/.rodata/.bss sections such that we can directly
load the address of them with minimal additional infrastructure
required. Loader support has been added in subsequent commits for
libbpf library.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Minor comment merge conflict in mlx5.
Staging driver has a fixup due to the skb->xmit_more changes
in 'net-next', but was removed in 'net'.
Signed-off-by: David S. Miller <davem@davemloft.net>
check_stack_access() that prints verbose log is used in
adjust_ptr_min_max_vals() that prints its own verbose log and now they
stick together, e.g.:
variable stack access var_off=(0xfffffffffffffff0; 0x4) off=-16
size=1R2 stack pointer arithmetic goes out of range, prohibited for
!root
Add missing newline so that log is more readable:
variable stack access var_off=(0xfffffffffffffff0; 0x4) off=-16 size=1
R2 stack pointer arithmetic goes out of range, prohibited for !root
Fixes: f1174f77b5 ("bpf/verifier: rework value tracking")
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
As discussed in [1] max value of variable offset has to be checked for
overflow on stack access otherwise verifier would accept code like this:
0: (b7) r2 = 6
1: (b7) r3 = 28
2: (7a) *(u64 *)(r10 -16) = 0
3: (7a) *(u64 *)(r10 -8) = 0
4: (79) r4 = *(u64 *)(r1 +168)
5: (c5) if r4 s< 0x0 goto pc+4
R1=ctx(id=0,off=0,imm=0) R2=inv6 R3=inv28
R4=inv(id=0,umax_value=9223372036854775807,var_off=(0x0;
0x7fffffffffffffff)) R10=fp0,call_-1 fp-8=mmmmmmmm fp-16=mmmmmmmm
6: (17) r4 -= 16
7: (0f) r4 += r10
8: (b7) r5 = 8
9: (85) call bpf_getsockopt#57
10: (b7) r0 = 0
11: (95) exit
, where R4 obviosly has unbounded max value.
Fix it by checking that reg->smax_value is inside (-BPF_MAX_VAR_OFF;
BPF_MAX_VAR_OFF) range.
reg->smax_value is used instead of reg->umax_value because stack
pointers are calculated using negative offset from fp. This is opposite
to e.g. map access where offset must be non-negative and where
umax_value is used.
Also dedicated verbose logs are added for both min and max bound check
failures to have diagnostics consistent with variable offset handling in
check_map_access().
[1] https://marc.info/?l=linux-netdev&m=155433357510597&w=2
Fixes: 2011fccfb6 ("bpf: Support variable offset stack access from helpers")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Proper support of indirect stack access with variable offset in
unprivileged mode (!root) requires corresponding support in Spectre
masking for stack ALU in retrieve_ptr_limit().
There are no use-case for variable offset in unprivileged mode though so
make verifier reject such accesses for simplicity.
Pointer arithmetics is one (and only?) way to cause variable offset and
it's already rejected in unpriv mode so that verifier won't even get to
helper function whose argument contains variable offset, e.g.:
0: (7a) *(u64 *)(r10 -16) = 0
1: (7a) *(u64 *)(r10 -8) = 0
2: (61) r2 = *(u32 *)(r1 +0)
3: (57) r2 &= 4
4: (17) r2 -= 16
5: (0f) r2 += r10
variable stack access var_off=(0xfffffffffffffff0; 0x4) off=-16 size=1R2
stack pointer arithmetic goes out of range, prohibited for !root
Still it looks like a good idea to reject variable offset indirect stack
access for unprivileged mode in check_stack_boundary() explicitly.
Fixes: 2011fccfb6 ("bpf: Support variable offset stack access from helpers")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
It's hard to guarantee that whole memory is marked as initialized on
helper return if uninitialized stack is accessed with variable offset
since specific bounds are unknown to verifier. This may cause
uninitialized stack leaking.
Reject such an access in check_stack_boundary to prevent possible
leaking.
There are no known use-cases for indirect uninitialized stack access
with variable offset so it shouldn't break anything.
Fixes: 2011fccfb6 ("bpf: Support variable offset stack access from helpers")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
The existing 16Mbyte verifier log limit is not enough for log_level=2
even for small programs. Increase it to 1Gbyte.
Note it's not a kernel memory limit.
It's an amount of memory user space provides to store
the verifier log. The kernel populates it 1k at a time.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Large verifier speed improvements allow to increase
verifier complexity limit.
Now regardless of the program composition and its size it takes
little time for the verifier to hit insn_processed limit.
On typical x86 machine non-debug kernel processes 1M instructions
in 1/10 of a second.
(before these speed improvements specially crafted programs
could be hitting multi-second verification times)
Full kasan kernel with debug takes ~1 second for the same 1M insns.
Hence bump the BPF_COMPLEXITY_LIMIT_INSNS limit to 1M.
Also increase the number of instructions per program
from 4k to internal BPF_COMPLEXITY_LIMIT_INSNS limit.
4k limit was confusing to users, since small programs with hundreds
of insns could be hitting BPF_COMPLEXITY_LIMIT_INSNS limit.
Sometimes adding more insns and bpf_trace_printk debug statements
would make the verifier accept the program while removing
code would make the verifier reject it.
Some user space application started to add #define MAX_FOO to
their programs and do:
MAX_FOO=100;
again:
compile with MAX_FOO;
try to load;
if (fails_to_load) { reduce MAX_FOO; goto again; }
to be able to fit maximum amount of processing into single program.
Other users artificially split their single program into a set of programs
and use all 32 iterations of tail_calls to increase compute limits.
And the most advanced folks used unlimited tc-bpf filter list
to execute many bpf programs.
Essentially the users managed to workaround 4k insn limit.
This patch removes the limit for root programs from uapi.
BPF_COMPLEXITY_LIMIT_INSNS is the kernel internal limit
and success to load the program no longer depends on program size,
but on 'smartness' of the verifier only.
The verifier will continue to get smarter with every kernel release.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Larger programs may trigger 16-bit jump offset overflow check
during instruction patching. Make this error verbose otherwise
users cannot decipher error code without printks in the verifier.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Temporary arrays used during program verification need to be vmalloc-ed
to support large bpf programs.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
With large verifier speed improvement brought by the previous patch
mark_reg_read() becomes the hottest function during verification.
On a typical program it consumes 40% of cpu.
mark_reg_read() walks parentage chain of registers to mark parents as LIVE_READ.
Once the register is marked there is no need to remark it again in the future.
Hence stop walking the chain once first LIVE_READ is seen.
This optimization drops mark_reg_read() time from 40% of cpu to <1%
and overall 2x improvement of verification speed.
For some programs the longest_mark_read_walk counter improves from ~500 to ~5
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Branch instructions, branch targets and calls in a bpf program are
the places where the verifier remembers states that led to successful
verification of the program.
These states are used to prune brute force program analysis.
For unprivileged programs there is a limit of 64 states per such
'branching' instructions (maximum length is tracked by max_states_per_insn
counter introduced in the previous patch).
Simply reducing this threshold to 32 or lower increases insn_processed
metric to the point that small valid programs get rejected.
For root programs there is no limit and cilium programs can have
max_states_per_insn to be 100 or higher.
Walking 100+ states multiplied by number of 'branching' insns during
verification consumes significant amount of cpu time.
Turned out simple LRU-like mechanism can be used to remove states
that unlikely will be helpful in future search pruning.
This patch introduces hit_cnt and miss_cnt counters:
hit_cnt - this many times this state successfully pruned the search
miss_cnt - this many times this state was not equivalent to other states
(and that other states were added to state list)
The heuristic introduced in this patch is:
if (sl->miss_cnt > sl->hit_cnt * 3 + 3)
/* drop this state from future considerations */
Higher numbers increase max_states_per_insn (allow more states to be
considered for pruning) and slow verification speed, but do not meaningfully
reduce insn_processed metric.
Lower numbers drop too many states and insn_processed increases too much.
Many different formulas were considered.
This one is simple and works well enough in practice.
(the analysis was done on selftests/progs/* and on cilium programs)
The end result is this heuristic improves verification speed by 10 times.
Large synthetic programs that used to take a second more now take
1/10 of a second.
In cases where max_states_per_insn used to be 100 or more, now it's ~10.
There is a slight increase in insn_processed for cilium progs:
before after
bpf_lb-DLB_L3.o 1831 1838
bpf_lb-DLB_L4.o 3029 3218
bpf_lb-DUNKNOWN.o 1064 1064
bpf_lxc-DDROP_ALL.o 26309 26935
bpf_lxc-DUNKNOWN.o 33517 34439
bpf_netdev.o 9713 9721
bpf_overlay.o 6184 6184
bpf_lcx_jit.o 37335 39389
And 2-3 times improvement in the verification speed.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
In order to understand the verifier bottlenecks add various stats
and extend log_level:
log_level 1 and 2 are kept as-is:
bit 0 - level=1 - print every insn and verifier state at branch points
bit 1 - level=2 - print every insn and verifier state at every insn
bit 2 - level=4 - print verifier error and stats at the end of verification
When verifier rejects the program the libbpf is trying to load the program twice.
Once with log_level=0 (no messages, only error code is reported to user space)
and second time with log_level=1 to tell the user why the verifier rejected it.
With introduction of bit 2 - level=4 the libbpf can choose to always use that
level and load programs once, since the verification speed is not affected and
in case of error the verbose message will be available.
Note that the verifier stats are not part of uapi just like all other
verbose messages. They're expected to change in the future.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Currently there is a difference in how verifier checks memory access for
helper arguments for PTR_TO_MAP_VALUE and PTR_TO_STACK with regard to
variable part of offset.
check_map_access, that is used for PTR_TO_MAP_VALUE, can handle variable
offsets just fine, so that BPF program can call a helper like this:
some_helper(map_value_ptr + off, size);
, where offset is unknown at load time, but is checked by program to be
in a safe rage (off >= 0 && off + size < map_value_size).
But it's not the case for check_stack_boundary, that is used for
PTR_TO_STACK, and same code with pointer to stack is rejected by
verifier:
some_helper(stack_value_ptr + off, size);
For example:
0: (7a) *(u64 *)(r10 -16) = 0
1: (7a) *(u64 *)(r10 -8) = 0
2: (61) r2 = *(u32 *)(r1 +0)
3: (57) r2 &= 4
4: (17) r2 -= 16
5: (0f) r2 += r10
6: (18) r1 = 0xffff888111343a80
8: (85) call bpf_map_lookup_elem#1
invalid variable stack read R2 var_off=(0xfffffffffffffff0; 0x4)
Add support for variable offset access to check_stack_boundary so that
if offset is checked by program to be in a safe range it's accepted by
verifier.
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
The BPF verifier checks the maximum number of call stack frames twice,
first in the main CFG traversal (do_check) and then in a subsequent
traversal (check_max_stack_depth). If the second check fails, it logs a
'verifier bug' warning and errors out, as the number of call stack frames
should have been verified already.
However, the second check may fail without indicating a verifier bug: if
the excessive function calls reside in dead code, the main CFG traversal
may not visit them; the subsequent traversal visits all instructions,
including dead code.
This case raises the question of how invalid dead code should be treated.
This patch implements the conservative option and rejects such code.
Signed-off-by: Paul Chaignon <paul.chaignon@orange.com>
Tested-by: Xiao Han <xiao.han@orange.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Commit 7640ead939 ("bpf: verifier: make sure callees don't prune
with caller differences") connected up parentage chains of all
frames of the stack. It didn't, however, ensure propagate_liveness()
propagates all liveness information along those chains.
This means pruning happening in the callee may generate explored
states with incomplete liveness for the chains in lower frames
of the stack.
The included selftest is similar to the prior one from commit
7640ead939 ("bpf: verifier: make sure callees don't prune with
caller differences"), where callee would prune regardless of the
difference in r8 state.
Now we also initialize r9 to 0 or 1 based on a result from get_random().
r9 is never read so the walk with r9 = 0 gets pruned (correctly) after
the walk with r9 = 1 completes.
The selftest is so arranged that the pruning will happen in the
callee. Since callee does not propagate read marks of r8, the
explored state at the pruning point prior to the callee will
now ignore r8.
Propagate liveness on all frames of the stack when pruning.
Fixes: f4d7e40a5b ("bpf: introduce function calls (verification)")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Allow looking up a sock_common. This gives eBPF programs
access to timewait and request sockets.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
It's currently not possible to access timewait or request sockets
from eBPF, since there is no way to return a PTR_TO_SOCK_COMMON
from a helper. Introduce RET_PTR_TO_SOCK_COMMON to enable this
behaviour.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
So far, the verifier only acquires reference tracking state for
RET_PTR_TO_SOCKET_OR_NULL. Instead of extending this for every
new return type which desires these semantics, acquire reference
tracking state iff the called helper is an acquire function.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Syzkaller hit 'KASAN: use-after-free Write in sanitize_ptr_alu' bug.
Call trace:
dump_stack+0xbf/0x12e
print_address_description+0x6a/0x280
kasan_report+0x237/0x360
sanitize_ptr_alu+0x85a/0x8d0
adjust_ptr_min_max_vals+0x8f2/0x1ca0
adjust_reg_min_max_vals+0x8ed/0x22e0
do_check+0x1ca6/0x5d00
bpf_check+0x9ca/0x2570
bpf_prog_load+0xc91/0x1030
__se_sys_bpf+0x61e/0x1f00
do_syscall_64+0xc8/0x550
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Fault injection trace:
kfree+0xea/0x290
free_func_state+0x4a/0x60
free_verifier_state+0x61/0xe0
push_stack+0x216/0x2f0 <- inject failslab
sanitize_ptr_alu+0x2b1/0x8d0
adjust_ptr_min_max_vals+0x8f2/0x1ca0
adjust_reg_min_max_vals+0x8ed/0x22e0
do_check+0x1ca6/0x5d00
bpf_check+0x9ca/0x2570
bpf_prog_load+0xc91/0x1030
__se_sys_bpf+0x61e/0x1f00
do_syscall_64+0xc8/0x550
entry_SYSCALL_64_after_hwframe+0x49/0xbe
When kzalloc() fails in push_stack(), free_verifier_state() will free
current verifier state. As push_stack() returns, dst_reg was restored
if ptr_is_dst_reg is false. However, as member of the cur_state,
dst_reg is also freed, and error occurs when dereferencing dst_reg.
Simply fix it by testing ret of push_stack() before restoring dst_reg.
Fixes: 979d63d50c ("bpf: prevent out of bounds speculation on pointer arithmetic")
Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Naresh reported that test_align fails because of the mismatch at the
verbose printout of the register states. The reason is due to the newly
added ref_obj_id.
ref_obj_id is only useful for refcounted reg. Thus, this patch fixes it
by only printing ref_obj_id for refcounted reg. While at it, it also uses
comma instead of space to separate between "id" and "ref_obj_id".
Fixes: 1b98658968 ("bpf: Fix bpf_tcp_sock and bpf_sk_fullsock issue related to bpf_sk_release")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Lorenz Bauer [thanks!] reported that a ptr returned by bpf_tcp_sock(sk)
can still be accessed after bpf_sk_release(sk).
Both bpf_tcp_sock() and bpf_sk_fullsock() have the same issue.
This patch addresses them together.
A simple reproducer looks like this:
sk = bpf_sk_lookup_tcp();
/* if (!sk) ... */
tp = bpf_tcp_sock(sk);
/* if (!tp) ... */
bpf_sk_release(sk);
snd_cwnd = tp->snd_cwnd; /* oops! The verifier does not complain. */
The problem is the verifier did not scrub the register's states of
the tcp_sock ptr (tp) after bpf_sk_release(sk).
[ Note that when calling bpf_tcp_sock(sk), the sk is not always
refcount-acquired. e.g. bpf_tcp_sock(skb->sk). The verifier works
fine for this case. ]
Currently, the verifier does not track if a helper's return ptr (in REG_0)
is "carry"-ing one of its argument's refcount status. To carry this info,
the reg1->id needs to be stored in reg0.
One approach was tried, like "reg0->id = reg1->id", when calling
"bpf_tcp_sock()". The main idea was to avoid adding another "ref_obj_id"
for the same reg. However, overlapping the NULL marking and ref
tracking purpose in one "id" does not work well:
ref_sk = bpf_sk_lookup_tcp();
fullsock = bpf_sk_fullsock(ref_sk);
tp = bpf_tcp_sock(ref_sk);
if (!fullsock) {
bpf_sk_release(ref_sk);
return 0;
}
/* fullsock_reg->id is marked for NOT-NULL.
* Same for tp_reg->id because they have the same id.
*/
/* oops. verifier did not complain about the missing !tp check */
snd_cwnd = tp->snd_cwnd;
Hence, a new "ref_obj_id" is needed in "struct bpf_reg_state".
With a new ref_obj_id, when bpf_sk_release(sk) is called, the verifier can
scrub all reg states which has a ref_obj_id match. It is done with the
changes in release_reg_references() in this patch.
While fixing it, sk_to_full_sk() is removed from bpf_tcp_sock() and
bpf_sk_fullsock() to avoid these helpers from returning
another ptr. It will make bpf_sk_release(tp) possible:
sk = bpf_sk_lookup_tcp();
/* if (!sk) ... */
tp = bpf_tcp_sock(sk);
/* if (!tp) ... */
bpf_sk_release(tp);
A separate helper "bpf_get_listener_sock()" will be added in a later
patch to do sk_to_full_sk().
Misc change notes:
- To allow bpf_sk_release(tp), the arg of bpf_sk_release() is changed
from ARG_PTR_TO_SOCKET to ARG_PTR_TO_SOCK_COMMON. ARG_PTR_TO_SOCKET
is removed from bpf.h since no helper is using it.
- arg_type_is_refcounted() is renamed to arg_type_may_be_refcounted()
because ARG_PTR_TO_SOCK_COMMON is the only one and skb->sk is not
refcounted. All bpf_sk_release(), bpf_sk_fullsock() and bpf_tcp_sock()
take ARG_PTR_TO_SOCK_COMMON.
- check_refcount_ok() ensures is_acquire_function() cannot take
arg_type_may_be_refcounted() as its argument.
- The check_func_arg() can only allow one refcount-ed arg. It is
guaranteed by check_refcount_ok() which ensures at most one arg can be
refcounted. Hence, it is a verifier internal error if >1 refcount arg
found in check_func_arg().
- In release_reference(), release_reference_state() is called
first to ensure a match on "reg->ref_obj_id" can be found before
scrubbing the reg states with release_reg_references().
- reg_is_refcounted() is no longer needed.
1. In mark_ptr_or_null_regs(), its usage is replaced by
"ref_obj_id && ref_obj_id == id" because,
when is_null == true, release_reference_state() should only be
called on the ref_obj_id obtained by a acquire helper (i.e.
is_acquire_function() == true). Otherwise, the following
would happen:
sk = bpf_sk_lookup_tcp();
/* if (!sk) { ... } */
fullsock = bpf_sk_fullsock(sk);
if (!fullsock) {
/*
* release_reference_state(fullsock_reg->ref_obj_id)
* where fullsock_reg->ref_obj_id == sk_reg->ref_obj_id.
*
* Hence, the following bpf_sk_release(sk) will fail
* because the ref state has already been released in the
* earlier release_reference_state(fullsock_reg->ref_obj_id).
*/
bpf_sk_release(sk);
}
2. In release_reg_references(), the current reg_is_refcounted() call
is unnecessary because the id check is enough.
- The type_is_refcounted() and type_is_refcounted_or_null()
are no longer needed also because reg_is_refcounted() is removed.
Fixes: 655a51e536 ("bpf: Add struct bpf_tcp_sock and BPF_FUNC_tcp_sock")
Reported-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Non-zero imm value in the second part of the ldimm64 instruction for
BPF_PSEUDO_MAP_FD is invalid, and thus must be rejected. The map fd
only ever sits in the first instructions' imm field. None of the BPF
loaders known to us are using it, so risk of regression is minimal.
For clarity and consistency, the few insn->{src_reg,imm} occurrences
are rewritten into insn[0].{src_reg,imm}. Add a test case to the BPF
selftest suite as well.
Fixes: 0246e64d9a ("bpf: handle pseudo BPF_LD_IMM64 insn")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Daniel Borkmann says:
====================
pull-request: bpf-next 2019-03-04
The following pull-request contains BPF updates for your *net-next* tree.
The main changes are:
1) Add AF_XDP support to libbpf. Rationale is to facilitate writing
AF_XDP applications by offering higher-level APIs that hide many
of the details of the AF_XDP uapi. Sample programs are converted
over to this new interface as well, from Magnus.
2) Introduce a new cant_sleep() macro for annotation of functions
that cannot sleep and use it in BPF_PROG_RUN() to assert that
BPF programs run under preemption disabled context, from Peter.
3) Introduce per BPF prog stats in order to monitor the usage
of BPF; this is controlled by kernel.bpf_stats_enabled sysctl
knob where monitoring tools can make use of this to efficiently
determine the average cost of programs, from Alexei.
4) Split up BPF selftest's test_progs similarly as we already
did with test_verifier. This allows to further reduce merge
conflicts in future and to get more structure into our
quickly growing BPF selftest suite, from Stanislav.
5) Fix a bug in BTF's dedup algorithm which can cause an infinite
loop in some circumstances; also various BPF doc fixes and
improvements, from Andrii.
6) Various BPF sample cleanups and migration to libbpf in order
to further isolate the old sample loader code (so we can get
rid of it at some point), from Jakub.
7) Add a new BPF helper for BPF cgroup skb progs that allows
to set ECN CE code point and a Host Bandwidth Manager (HBM)
sample program for limiting the bandwidth used by v2 cgroups,
from Lawrence.
8) Enable write access to skb->queue_mapping from tc BPF egress
programs in order to let BPF pick TX queue, from Jesper.
9) Fix a bug in BPF spinlock handling for map-in-map which did
not propagate spin_lock_off to the meta map, from Yonghong.
10) Fix a bug in the new per-CPU BPF prog counters to properly
initialize stats for each CPU, from Eric.
11) Add various BPF helper prototypes to selftest's bpf_helpers.h,
from Willem.
12) Fix various BPF samples bugs in XDP and tracing progs,
from Toke, Daniel and Yonghong.
13) Silence preemption splat in test_bpf after BPF_PROG_RUN()
enforces it now everywhere, from Anders.
14) Fix a signedness bug in libbpf's btf_dedup_ref_type() to
get error handling working, from Dan.
15) Fix bpftool documentation and auto-completion with regards
to stream_{verdict,parser} attach types, from Alban.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
Marek reported that he saw an issue with the below snippet in that
timing measurements where off when loaded as unpriv while results
were reasonable when loaded as privileged:
[...]
uint64_t a = bpf_ktime_get_ns();
uint64_t b = bpf_ktime_get_ns();
uint64_t delta = b - a;
if ((int64_t)delta > 0) {
[...]
Turns out there is a bug where a corner case is missing in the fix
d3bd7413e0 ("bpf: fix sanitation of alu op with pointer / scalar
type from different paths"), namely fixup_bpf_calls() only checks
whether aux has a non-zero alu_state, but it also needs to test for
the case of BPF_ALU_NON_POINTER since in both occasions we need to
skip the masking rewrite (as there is nothing to mask).
Fixes: d3bd7413e0 ("bpf: fix sanitation of alu op with pointer / scalar type from different paths")
Reported-by: Marek Majkowski <marek@cloudflare.com>
Reported-by: Arthur Fabre <afabre@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/netdev/CAJPywTJqP34cK20iLM5YmUMz9KXQOdu1-+BZrGMAGgLuBWz7fg@mail.gmail.com/T/
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
JITed BPF programs are indistinguishable from kernel functions, but unlike
kernel code BPF code can be changed often.
Typical approach of "perf record" + "perf report" profiling and tuning of
kernel code works just as well for BPF programs, but kernel code doesn't
need to be monitored whereas BPF programs do.
Users load and run large amount of BPF programs.
These BPF stats allow tools monitor the usage of BPF on the server.
The monitoring tools will turn sysctl kernel.bpf_stats_enabled
on and off for few seconds to sample average cost of the programs.
Aggregated data over hours and days will provide an insight into cost of BPF
and alarms can trigger in case given program suddenly gets more expensive.
The cost of two sched_clock() per program invocation adds ~20 nsec.
Fast BPF progs (like selftests/bpf/progs/test_pkt_access.c) will slow down
from ~10 nsec to ~30 nsec.
static_key minimizes the cost of the stats collection.
There is no measurable difference before/after this patch
with kernel.bpf_stats_enabled=0
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This patch adds a helper function BPF_FUNC_tcp_sock and it
is currently available for cg_skb and sched_(cls|act):
struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock *sk);
int cg_skb_foo(struct __sk_buff *skb) {
struct bpf_tcp_sock *tp;
struct bpf_sock *sk;
__u32 snd_cwnd;
sk = skb->sk;
if (!sk)
return 1;
tp = bpf_tcp_sock(sk);
if (!tp)
return 1;
snd_cwnd = tp->snd_cwnd;
/* ... */
return 1;
}
A 'struct bpf_tcp_sock' is also added to the uapi bpf.h to provide
read-only access. bpf_tcp_sock has all the existing tcp_sock's fields
that has already been exposed by the bpf_sock_ops.
i.e. no new tcp_sock's fields are exposed in bpf.h.
This helper returns a pointer to the tcp_sock. If it is not a tcp_sock
or it cannot be traced back to a tcp_sock by sk_to_full_sk(), it
returns NULL. Hence, the caller needs to check for NULL before
accessing it.
The current use case is to expose members from tcp_sock
to allow a cg_skb_bpf_prog to provide per cgroup traffic
policing/shaping.
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
In kernel, it is common to check "skb->sk && sk_fullsock(skb->sk)"
before accessing the fields in sock. For example, in __netdev_pick_tx:
static u16 __netdev_pick_tx(struct net_device *dev, struct sk_buff *skb,
struct net_device *sb_dev)
{
/* ... */
struct sock *sk = skb->sk;
if (queue_index != new_index && sk &&
sk_fullsock(sk) &&
rcu_access_pointer(sk->sk_dst_cache))
sk_tx_queue_set(sk, new_index);
/* ... */
return queue_index;
}
This patch adds a "struct bpf_sock *sk" pointer to the "struct __sk_buff"
where a few of the convert_ctx_access() in filter.c has already been
accessing the skb->sk sock_common's fields,
e.g. sock_ops_convert_ctx_access().
"__sk_buff->sk" is a PTR_TO_SOCK_COMMON_OR_NULL in the verifier.
Some of the fileds in "bpf_sock" will not be directly
accessible through the "__sk_buff->sk" pointer. It is limited
by the new "bpf_sock_common_is_valid_access()".
e.g. The existing "type", "protocol", "mark" and "priority" in bpf_sock
are not allowed.
The newly added "struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)"
can be used to get a sk with all accessible fields in "bpf_sock".
This helper is added to both cg_skb and sched_(cls|act).
int cg_skb_foo(struct __sk_buff *skb) {
struct bpf_sock *sk;
sk = skb->sk;
if (!sk)
return 1;
sk = bpf_sk_fullsock(sk);
if (!sk)
return 1;
if (sk->family != AF_INET6 || sk->protocol != IPPROTO_TCP)
return 1;
/* some_traffic_shaping(); */
return 1;
}
(1) The sk is read only
(2) There is no new "struct bpf_sock_common" introduced.
(3) Future kernel sock's members could be added to bpf_sock only
instead of repeatedly adding at multiple places like currently
in bpf_sock_ops_md, bpf_sock_addr_md, sk_reuseport_md...etc.
(4) After "sk = skb->sk", the reg holding sk is in type
PTR_TO_SOCK_COMMON_OR_NULL.
(5) After bpf_sk_fullsock(), the return type will be in type
PTR_TO_SOCKET_OR_NULL which is the same as the return type of
bpf_sk_lookup_xxx().
However, bpf_sk_fullsock() does not take refcnt. The
acquire_reference_state() is only depending on the return type now.
To avoid it, a new is_acquire_function() is checked before calling
acquire_reference_state().
(6) The WARN_ON in "release_reference_state()" is no longer an
internal verifier bug.
When reg->id is not found in state->refs[], it means the
bpf_prog does something wrong like
"bpf_sk_release(bpf_sk_fullsock(skb->sk))" where reference has
never been acquired by calling "bpf_sk_fullsock(skb->sk)".
A -EINVAL and a verbose are done instead of WARN_ON. A test is
added to the test_verifier in a later patch.
Since the WARN_ON in "release_reference_state()" is no longer
needed, "__release_reference_state()" is folded into
"release_reference_state()" also.
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Introduce 'struct bpf_spin_lock' and bpf_spin_lock/unlock() helpers to let
bpf program serialize access to other variables.
Example:
struct hash_elem {
int cnt;
struct bpf_spin_lock lock;
};
struct hash_elem * val = bpf_map_lookup_elem(&hash_map, &key);
if (val) {
bpf_spin_lock(&val->lock);
val->cnt++;
bpf_spin_unlock(&val->lock);
}
Restrictions and safety checks:
- bpf_spin_lock is only allowed inside HASH and ARRAY maps.
- BTF description of the map is mandatory for safety analysis.
- bpf program can take one bpf_spin_lock at a time, since two or more can
cause dead locks.
- only one 'struct bpf_spin_lock' is allowed per map element.
It drastically simplifies implementation yet allows bpf program to use
any number of bpf_spin_locks.
- when bpf_spin_lock is taken the calls (either bpf2bpf or helpers) are not allowed.
- bpf program must bpf_spin_unlock() before return.
- bpf program can access 'struct bpf_spin_lock' only via
bpf_spin_lock()/bpf_spin_unlock() helpers.
- load/store into 'struct bpf_spin_lock lock;' field is not allowed.
- to use bpf_spin_lock() helper the BTF description of map value must be
a struct and have 'struct bpf_spin_lock anyname;' field at the top level.
Nested lock inside another struct is not allowed.
- syscall map_lookup doesn't copy bpf_spin_lock field to user space.
- syscall map_update and program map_update do not update bpf_spin_lock field.
- bpf_spin_lock cannot be on the stack or inside networking packet.
bpf_spin_lock can only be inside HASH or ARRAY map value.
- bpf_spin_lock is available to root only and to all program types.
- bpf_spin_lock is not allowed in inner maps of map-in-map.
- ld_abs is not allowed inside spin_lock-ed region.
- tracing progs and socket filter progs cannot use bpf_spin_lock due to
insufficient preemption checks
Implementation details:
- cgroup-bpf class of programs can nest with xdp/tc programs.
Hence bpf_spin_lock is equivalent to spin_lock_irqsave.
Other solutions to avoid nested bpf_spin_lock are possible.
Like making sure that all networking progs run with softirq disabled.
spin_lock_irqsave is the simplest and doesn't add overhead to the
programs that don't use it.
- arch_spinlock_t is used when its implemented as queued_spin_lock
- archs can force their own arch_spinlock_t
- on architectures where queued_spin_lock is not available and
sizeof(arch_spinlock_t) != sizeof(__u32) trivial lock is used.
- presence of bpf_spin_lock inside map value could have been indicated via
extra flag during map_create, but specifying it via BTF is cleaner.
It provides introspection for map key/value and reduces user mistakes.
Next steps:
- allow bpf_spin_lock in other map types (like cgroup local storage)
- introduce BPF_F_LOCK flag for bpf_map_update() syscall and helper
to request kernel to grab bpf_spin_lock before rewriting the value.
That will serialize access to map elements.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Krzesimir Nowak