netdev - Re: [PATCH bpf v2] bpf: relax return code check for subprograms

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Message-ID: <CAEf4Bzbjx8Hpozi9eaa2da2K9WbA_xA0tVrp_+3DHN4GgKmeXw@mail.gmail.com>
Date:   Fri, 13 Nov 2020 12:06:50 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Dmitrii Banshchikov <me@...que.spb.ru>
Cc:     bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com>,
        Andrey Ignatov <rdna@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf v2] bpf: relax return code check for subprograms

On Fri, Nov 13, 2020 at 9:18 AM Dmitrii Banshchikov <me@...que.spb.ru> wrote:
>
> Currently verifier enforces return code checks for subprograms in the
> same manner as it does for program entry points. This prevents returning
> arbitrary scalar values from subprograms. Scalar type of returned values
> is checked by btf_prepare_func_args() and hence it should be safe to
> allow only scalars for now. Relax return code checks for subprograms and
> allow any correct scalar values.
>
> Signed-off-by: Dmitrii Banshchikov <me@...que.spb.ru>
> Fixes: 51c39bb1d5d10 (bpf: Introduce function-by-function verification)
> ---

LGTM!

Acked-by: Andrii Nakryiko <andrii@...nel.org>

> v1 -> v2:
>  - Move is_subprog flag determination to check_return_code()
>  - Remove unneeded intermediate function from tests
>  - Use __noinline instead of __attribute__((noinline)) in tests
>
>  kernel/bpf/verifier.c                         | 15 +++++++++++++--
>  .../bpf/prog_tests/test_global_funcs.c        |  1 +
>  .../selftests/bpf/progs/test_global_func8.c   | 19 +++++++++++++++++++
>  3 files changed, 33 insertions(+), 2 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/test_global_func8.c
>

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