Commit caff1fa4 authored by Menglong Dong's avatar Menglong Dong Committed by Daniel Borkmann

bpf: Fix probe read error in ___bpf_prog_run()

I think there is something wrong with BPF_PROBE_MEM in ___bpf_prog_run()
in big-endian machine. Let's make a test and see what will happen if we
want to load a 'u16' with BPF_PROBE_MEM.

Let's make the src value '0x0001', the value of dest register will become
0x0001000000000000, as the value will be loaded to the first 2 byte of
DST with following code:

  bpf_probe_read_kernel(&DST, SIZE, (const void *)(long) (SRC + insn->off));

Obviously, the value in DST is not correct. In fact, we can compare
BPF_PROBE_MEM with LDX_MEM_H:

  DST = *(SIZE *)(unsigned long) (SRC + insn->off);

If the memory load is done by LDX_MEM_H, the value in DST will be 0x1 now.

And I think this error results in the test case 'test_bpf_sk_storage_map'
failing:

  test_bpf_sk_storage_map:PASS:bpf_iter_bpf_sk_storage_map__open_and_load 0 nsec
  test_bpf_sk_storage_map:PASS:socket 0 nsec
  test_bpf_sk_storage_map:PASS:map_update 0 nsec
  test_bpf_sk_storage_map:PASS:socket 0 nsec
  test_bpf_sk_storage_map:PASS:map_update 0 nsec
  test_bpf_sk_storage_map:PASS:socket 0 nsec
  test_bpf_sk_storage_map:PASS:map_update 0 nsec
  test_bpf_sk_storage_map:PASS:attach_iter 0 nsec
  test_bpf_sk_storage_map:PASS:create_iter 0 nsec
  test_bpf_sk_storage_map:PASS:read 0 nsec
  test_bpf_sk_storage_map:FAIL:ipv6_sk_count got 0 expected 3
  $10/26 bpf_iter/bpf_sk_storage_map:FAIL

The code of the test case is simply, it will load sk->sk_family to the
register with BPF_PROBE_MEM and check if it is AF_INET6. With this patch,
now the test case 'bpf_iter' can pass:

  $10  bpf_iter:OK

Fixes: 2a02759e ("bpf: Add support for BTF pointers to interpreter")
Signed-off-by: default avatarMenglong Dong <imagedong@tencent.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJiang Biao <benbjiang@tencent.com>
Reviewed-by: default avatarHao Peng <flyingpeng@tencent.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/bpf/20220524021228.533216-1-imagedong@tencent.com
parent 59ed76fe
...@@ -1953,6 +1953,11 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) ...@@ -1953,6 +1953,11 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
CONT; \ CONT; \
LDX_MEM_##SIZEOP: \ LDX_MEM_##SIZEOP: \
DST = *(SIZE *)(unsigned long) (SRC + insn->off); \ DST = *(SIZE *)(unsigned long) (SRC + insn->off); \
CONT; \
LDX_PROBE_MEM_##SIZEOP: \
bpf_probe_read_kernel(&DST, sizeof(SIZE), \
(const void *)(long) (SRC + insn->off)); \
DST = *((SIZE *)&DST); \
CONT; CONT;
LDST(B, u8) LDST(B, u8)
...@@ -1960,15 +1965,6 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) ...@@ -1960,15 +1965,6 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
LDST(W, u32) LDST(W, u32)
LDST(DW, u64) LDST(DW, u64)
#undef LDST #undef LDST
#define LDX_PROBE(SIZEOP, SIZE) \
LDX_PROBE_MEM_##SIZEOP: \
bpf_probe_read_kernel(&DST, SIZE, (const void *)(long) (SRC + insn->off)); \
CONT;
LDX_PROBE(B, 1)
LDX_PROBE(H, 2)
LDX_PROBE(W, 4)
LDX_PROBE(DW, 8)
#undef LDX_PROBE
#define ATOMIC_ALU_OP(BOP, KOP) \ #define ATOMIC_ALU_OP(BOP, KOP) \
case BOP: \ case BOP: \
......
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