netdev - Re: [bpf-next PATCH 2/4] bpf: selftests, verifier case for non null pointer check branch taken

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Message-ID: <CAEf4BzZKC5B-Nas-o_TPgJWvbwbcXUZ_aeH1-CPgPf0QAZN_KA@mail.gmail.com>
Date:   Mon, 18 May 2020 22:05:26 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [bpf-next PATCH 2/4] bpf: selftests, verifier case for non null
 pointer check branch taken

On Mon, May 18, 2020 at 1:06 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> When we have pointer type that is known to be non-null we only follow
> the non-null branch. This adds tests to cover this case for reference
> tracking.
>
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
> ---
>  .../testing/selftests/bpf/verifier/ref_tracking.c  |   16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/verifier/ref_tracking.c b/tools/testing/selftests/bpf/verifier/ref_tracking.c
> index 604b461..d8f7c04 100644
> --- a/tools/testing/selftests/bpf/verifier/ref_tracking.c
> +++ b/tools/testing/selftests/bpf/verifier/ref_tracking.c
> @@ -821,3 +821,19 @@
>         .result = REJECT,
>         .errstr = "invalid mem access",
>  },
> +{
> +       "reference tracking: branch tracking valid pointer null comparison",
> +       .insns = {
> +       BPF_SK_LOOKUP(sk_lookup_tcp),
> +       BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
> +       BPF_MOV64_IMM(BPF_REG_3, 1),
> +       BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 0, 1),
> +       BPF_MOV64_IMM(BPF_REG_3, 0),
> +       BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 2),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
> +       BPF_EMIT_CALL(BPF_FUNC_sk_release),
> +       BPF_EXIT_INSN(),
> +       },
> +       .prog_type = BPF_PROG_TYPE_SCHED_CLS,
> +       .result = ACCEPT,
> +},

Can you please add another test where you test against non-zero value
to verify that both branches are considered to be taken and verifier
actually complaints that sk_release happens only in one of branches.

>