Re: [PATCH bpf v2 2/2] selftests/bpf: Add test for immediate spilled to stack

[Hao Sun]

On Wed, Nov 1, 2023 at 12:05 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> 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.
>

Yes, so I guess we can just drop the line number there, will send patch v3.

> 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/

Thanks.