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

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Message-ID: <CAEf4BzZ6gnXD23oxaKT3jB2t4kLVczmx+8q+n-KtyFWGv1ZqJw@mail.gmail.com>
Date:   Mon, 18 May 2020 22:03:35 -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 0/4] verifier, improve ptr is_branch_taken logic

On Mon, May 18, 2020 at 1:05 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> Verifier logic to track pointer is_branch_taken logic to prune paths
> that can not be taken. For many types we track if the pointer is null

I re-read first sentence many times, still not sure what it is saying.
Do you mind rephrasing it a bit for clarity? Thanks!

> or not. We can then use this information when calculating if branches
> are taken when jump is comparing if pointer is null or not.
>
> First patch is the verifier logic, patches 2/3 are tests for sock
> pointers and map values. The final patch adds a printk to one of
> the C test cases where the issue was initially reported. Feel free
> to drop this if we think its overkill. OTOH it keeps a nice test
> of a pattern folks might actually try and also doesn't add much in
> the way of test overhead.
>
> ---
>
> 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
>
>
>  .../selftests/bpf/progs/test_sk_lookup_kern.c      |    1 +
>  .../testing/selftests/bpf/verifier/ref_tracking.c  |   16 ++++++++++++++++
>  .../testing/selftests/bpf/verifier/value_or_null.c |   19 +++++++++++++++++++
>  3 files changed, 36 insertions(+)
>
> --
> Signature