hollalinux
/
linux-sg2042
mirror of https://github.com/sophgo/linux-riscv.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

bpf: fix narrower loads on s390 

The very first check in test_pkt_md_access is failing on s390, which
happens because loading a part of a struct __sk_buff field produces
an incorrect result.

The preprocessed code of the check is:

{
	__u8 tmp = *((volatile __u8 *)&skb->len +
		((sizeof(skb->len) - sizeof(__u8)) / sizeof(__u8)));
	if (tmp != ((*(volatile __u32 *)&skb->len) & 0xFF)) return 2;
};

clang generates the following code for it:

      0:	71 21 00 03 00 00 00 00	r2 = *(u8 *)(r1 + 3)
      1:	61 31 00 00 00 00 00 00	r3 = *(u32 *)(r1 + 0)
      2:	57 30 00 00 00 00 00 ff	r3 &= 255
      3:	5d 23 00 1d 00 00 00 00	if r2 != r3 goto +29 <LBB0_10>

Finally, verifier transforms it to:

  0: (61) r2 = *(u32 *)(r1 +104)
  1: (bc) w2 = w2
  2: (74) w2 >>= 24
  3: (bc) w2 = w2
  4: (54) w2 &= 255
  5: (bc) w2 = w2

The problem is that when verifier emits the code to replace a partial
load of a struct __sk_buff field (*(u8 *)(r1 + 3)) with a full load of
struct sk_buff field (*(u32 *)(r1 + 104)), an optional shift and a
bitwise AND, it assumes that the machine is little endian and
incorrectly decides to use a shift.

Adjust shift count calculation to account for endianness.

Fixes: 31fd85816d ("bpf: permits narrower load from bpf program context fields")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Ilya Leoshkevich 2019-07-19 11:18:15 +02:00 committed by Alexei Starovoitov
parent c8eee4135a
commit d9b8aadaff
2 changed files with 15 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
include/linux/filter.h
View File

@ -24,6 +24,7 @@
#include <net/sch_generic.h>
#include <asm/byteorder.h>
#include <uapi/linux/filter.h>
#include <uapi/linux/bpf.h>
@ -747,6 +748,18 @@ bpf_ctx_narrow_access_ok(u32 off, u32 size, u32 size_default)
return size <= size_default && (size & (size - 1)) == 0;
}
static inline u8
bpf_ctx_narrow_load_shift(u32 off, u32 size, u32 size_default)
{
u8 load_off = off & (size_default - 1);
#ifdef __LITTLE_ENDIAN
return load_off * 8;
#else
return (size_default - (load_off + size)) * 8;
#endif
}
#define bpf_ctx_wide_access_ok(off, size, type, field) \
(size == sizeof(__u64) && \
off >= offsetof(type, field) && \

4
kernel/bpf/verifier.c
View File

@ -8616,8 +8616,8 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
}
if (is_narrower_load && size < target_size) {
u8 shift = (off & (size_default - 1)) * 8;
u8 shift = bpf_ctx_narrow_load_shift(off, size,
size_default);
if (ctx_field_size <= 4) {
if (shift)
insn_buf[cnt++] = BPF_ALU32_IMM(BPF_RSH,