On Wed, 2023-11-01 at 08:33 +0100, Hao Sun wrote:
> Add a test to check if the verifier correctly reason about the sign
> of an immediate spilled to stack by BPF_ST instruction.
>
> Signed-off-by: Hao Sun <sunhao.th@xxxxxxxxx>
> ---
> tools/testing/selftests/bpf/verifier/bpf_st_mem.c | 32 +++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/verifier/bpf_st_mem.c b/tools/testing/selftests/bpf/verifier/bpf_st_mem.c
> index 3af2501082b2..0ba23807c46c 100644
> --- a/tools/testing/selftests/bpf/verifier/bpf_st_mem.c
> +++ b/tools/testing/selftests/bpf/verifier/bpf_st_mem.c
> @@ -65,3 +65,35 @@
> .expected_attach_type = BPF_SK_LOOKUP,
> .runs = -1,
> },
> +{
> + "BPF_ST_MEM stack imm sign",
> + /* Check if verifier correctly reasons about sign of an
> + * immediate spilled to stack by BPF_ST instruction.
> + *
> + * fp[-8] = -44;
> + * r0 = fp[-8];
> + * if r0 s< 0 goto ret0;
> + * r0 = -1;
> + * exit;
> + * ret0:
> + * r0 = 0;
> + * exit;
> + */
> + .insns = {
> + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, -44),
> + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8),
> + BPF_JMP_IMM(BPF_JSLT, BPF_REG_0, 0, 2),
> + BPF_MOV64_IMM(BPF_REG_0, -1),
> + BPF_EXIT_INSN(),
> + BPF_MOV64_IMM(BPF_REG_0, 0),
> + BPF_EXIT_INSN(),
> + },
> + /* Use prog type that requires return value in range [0, 1] */
> + .prog_type = BPF_PROG_TYPE_SK_LOOKUP,
> + .expected_attach_type = BPF_SK_LOOKUP,
> + .result = VERBOSE_ACCEPT,
> + .runs = -1,
> + .errstr = "0: (7a) *(u64 *)(r10 -8) = -44 ; R10=fp0 fp-8_w=-44\
> + 2: (c5) if r0 s< 0x0 goto pc+2\
> + 2: R0_w=-44",
> +},
>
Please note that this test case fails on CI [0], full log below:
2023-11-01T07:49:51.2841702Z #116/p BPF_ST_MEM stack imm sign FAIL
2023-11-01T07:49:51.2843456Z Unexpected verifier log!
2023-11-01T07:49:51.2844968Z EXP: 2: R0_w=-44
2023-11-01T07:49:51.2845583Z RES:
2023-11-01T07:49:51.2846693Z func#0 @0
2023-11-01T07:49:51.2848932Z 0: R1=ctx(off=0,imm=0) R10=fp0
2023-11-01T07:49:51.2853045Z 0: (7a) *(u64 *)(r10 -8) = -44 ; R10=fp0 fp-8_w=-44
2023-11-01T07:49:51.2857391Z 1: (79) r0 = *(u64 *)(r10 -8) ; R0_w=-44 R10=fp0 fp-8_w=-44
2023-11-01T07:49:51.2859127Z 2: (c5) if r0 s< 0x0 goto pc+2
2023-11-01T07:49:51.2862943Z mark_precise: frame0: last_idx 2 first_idx 0 subseq_idx -1
2023-11-01T07:49:51.2867511Z mark_precise: frame0: regs=r0 stack= before 1: (79) r0 = *(u64 *)(r10 -8)
2023-11-01T07:49:51.2872217Z mark_precise: frame0: regs= stack=-8 before 0: (7a) *(u64 *)(r10 -8) = -44
2023-11-01T07:49:51.2872816Z 5: R0_w=-44
2023-11-01T07:49:51.2875653Z 5: (b7) r0 = 0 ; R0_w=0
2023-11-01T07:49:51.2876493Z 6: (95) exit
I suspect that after recent logging fixes instruction number printed
after jump changed and that's why test case no longer passes.
Note: you can check CI status for submitted patch-sets using link [1].
[0] https://github.com/kernel-patches/bpf/actions/runs/6717053909/job/18254330860
[1] https://patchwork.kernel.org/project/netdevbpf/list/
