netdev - Re: [PATCH bpf-next v4 1/3] bpf: support input __sk_buff context in BPF_PROG_TEST

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Message-ID: <CAKH8qBsx2F-PY8NJ0Yh3rdNBNGGPnVd+EPiHSRhsLa5cRoA9Rw@mail.gmail.com>
Date:   Thu, 11 Apr 2019 15:25:44 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Netdev <netdev@...r.kernel.org>, bpf@...r.kernel.org,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>, Martin Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v4 1/3] bpf: support input __sk_buff context in BPF_PROG_TEST_RUN

On Thu, Apr 11, 2019 at 3:23 PM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> Hey Stanislav,
>
> On 04/09/2019 08:49 PM, Stanislav Fomichev wrote:
> > Add new set of arguments to bpf_attr for BPF_PROG_TEST_RUN:
> > * ctx_in/ctx_size_in - input context
> > * ctx_out/ctx_size_out - output context
> >
> > The intended use case is to pass some meta data to the test runs that
> > operate on skb (this has being brought up on recent LPC).
> >
> > For programs that use bpf_prog_test_run_skb, support __sk_buff input and
> > output. Initially, from input __sk_buff, copy _only_ cb and priority into
> > skb, all other non-zero fields are prohibited (with EINVAL).
> > If the user has set ctx_out/ctx_size_out, copy the potentially modified
> > __sk_buff back to the userspace.
> >
> > We require all fields of input __sk_buff except the ones we explicitly
> > support to be set to zero. The expectation is that in the future we might
> > add support for more fields and we want to fail explicitly if the user
> > runs the program on the kernel where we don't yet support them.
> >
> > The API is intentionally vague (i.e. we don't explicitly add __sk_buff
> > to bpf_attr, but ctx_in) to potentially let other test_run types use
> > this interface in the future (this can be xdp_md for xdp types for
> > example).
> >
> > v4:
> >   * don't copy more than allowed in bpf_ctx_init [Martin]
> >
> > v3:
> >   * handle case where ctx_in is NULL, but ctx_out is not [Martin]
> >   * convert size==0 checks to ptr==NULL checks and add some extra ptr
> >     checks [Martin]
> >
> > v2:
> >   * Addressed comments from Martin Lau
> >
> > Cc: Martin Lau <kafai@...com>
> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
>
> This still has a bug in that we need to reject !bpf_prog_test_run_skb() cases,
> since they are not handled by your set. So for e.g. XDP, flow dissector progs,
> we need to error out if ctx is set such that it can be safely extended in future.
> Please follow up.
Good point, sure, will follow up on that!

> Thanks,
> Daniel