netdev - Re: [bpf-next PATCH v2 0/4] ] verifier, improve ptr is_branch

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Date:   Thu, 21 May 2020 15:21:31 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Yonghong Song <yhs@...com>, 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 v2 0/4] ] verifier, improve ptr is_branch_taken logic

On Thu, May 21, 2020 at 1:07 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> This series adds logic to the verifier to handle the case where a
> pointer is known to be non-null but then the verifier encountesr a
> instruction, such as 'if ptr == 0 goto X' or 'if ptr != 0 goto X',
> where the pointer is compared against 0. Because the verifier tracks
> if a pointer may be null in many cases we can improve the branch
> tracking by following the case known to be true.
>
> The first patch adds the verifier logic and patches 2-4 add the
> test cases.
>
> v1->v2: fix verifier logic to return -1 indicating both paths must
> still be walked if value is not zero. Move mark_precision skip for
> this case into caller of mark_precision to ensure mark_precision can
> still catch other misuses. And add PTR_TYPE_BTF_ID to our list of
> supported types. Finally add one more test to catch the value not
> equal zero case. Thanks to Andrii for original review.
>
> Also fixed up commit messages hopefully its better now.
>

Yeah, much better, thanks! Few typos don't count ;)

For the series:

Acked-by: Andrii Nakryiko <andriin@...com>

> ---
>
> John Fastabend (4):
>       bpf: verifier track null pointer branch_taken with JNE and JEQ
>       bpf: selftests, verifier case for non null pointer check branch taken
>       bpf: selftests, verifier case for non null pointer map value branch
>       bpf: selftests, add printk to test_sk_lookup_kern to encode null ptr check
>
>
>  kernel/bpf/verifier.c                              |   36 ++++++++++++++++++--
>  .../selftests/bpf/progs/test_sk_lookup_kern.c      |    1 +
>  .../testing/selftests/bpf/verifier/ref_tracking.c  |   33 ++++++++++++++++++
>  .../testing/selftests/bpf/verifier/value_or_null.c |   19 +++++++++++
>  4 files changed, 86 insertions(+), 3 deletions(-)
>
> --
> Signature