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Date:   Mon, 18 May 2020 22:03:35 -0700
From:   Andrii Nakryiko <>
To:     John Fastabend <>
Cc:     Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Networking <>, bpf <>
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 <> 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

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