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: 39f6a120e988 ("bpf: Add support for BTF pointers to interpreter")
Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jiang Biao <benbjiang@tencent.com>
Reviewed-by: Hao Peng <flyingpeng@tencent.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/bpf/20220524021228.533216-1-imagedong@tencent.com

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index cacd8684c3c4c475b8e7b97785c38fdb4fbec27e..5f6f3f829b368aca466b07772a2938629ecb600f 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1953,6 +1953,11 @@ out:
                CONT;                                                   \
        LDX_MEM_##SIZEOP:                                               \
                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;
 
        LDST(B,   u8)
@@ -1960,15 +1965,6 @@ out:
        LDST(W,  u32)
        LDST(DW, u64)
 #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)                                                \
                case BOP:                                               \