netdev - Re: [PATCH v2 bpf-next 05/12] libbpf: auto-detect btf_id of raw

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Message-ID: <CAEf4BzZsz-6ftv628bk9LtEFr1qUoARL32x-kGagi7esOBURyA@mail.gmail.com>
Date:   Fri, 11 Oct 2019 21:38:06 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <ast@...com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        "x86@...nel.org" <x86@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 05/12] libbpf: auto-detect btf_id of raw_tracepoint

On Fri, Oct 11, 2019 at 6:29 PM Alexei Starovoitov <ast@...com> wrote:
>
> On 10/11/19 5:40 PM, Alexei Starovoitov wrote:
> >> But even if kernel supports attach_btf_id, I think users still need to
> >> opt in into specifying attach_btf_id by libbpf. Think about existing
> >> raw_tp programs that are using bpf_probe_read() because they were not
> >> created with this kernel feature in mind. They will suddenly stop
> >> working without any of user's fault.
> >
> > This one is excellent catch.
> > loop1.c should have caught it, since it has
> > SEC("raw_tracepoint/kfree_skb")
> > {
> >    int nested_loops(volatile struct pt_regs* ctx)
> >     .. = PT_REGS_RC(ctx);
> >
> > and verifier would have rejected it.
> > But the way the test is written it's not using libbpf's autodetect
> > of program type, so everything is passing.
>
> With:
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
> b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
> index 1c01ee2600a9..e27156dce10d 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
> @@ -67,7 +67,7 @@ void test_bpf_verif_scale(void)
>                   */
>                  { "pyperf600_nounroll.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
>
> -               { "loop1.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
> +               { "loop1.o", BPF_PROG_TYPE_UNSPEC},
>                  { "loop2.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
>
> libbpf prog auto-detection kicks in and ...
> # ./test_progs -n 3/10
> libbpf: load bpf program failed: Permission denied
> libbpf: -- BEGIN DUMP LOG ---
> libbpf:
> raw_tp 'kfree_skb' doesn't have 10-th argument
> invalid bpf_context access off=80 size=8
>
> Good :) The verifier is doing its job.

oh, another super intuitive error from verifier ;) 10th argument, what?..