From: Menglong Dong imagedong@tencent.com
[ Upstream commit caff1fa4118cec4dfd4336521ebd22a6408a1e3e ]
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: 2a02759ef5f8 ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/core.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 6e3ae90ad107..48eb9c329da6 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1652,6 +1652,11 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) 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) @@ -1659,15 +1664,6 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) 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: \