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Date:   Thu, 12 Sep 2019 11:46:39 +0100
From:   Toke Høiland-Jørgensen <>
To:     Sami Tolvanen <>
Cc:     Björn Töpel <>,
        Yonghong Song <>,
        Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Kees Cook <>, Martin Lau <>,
        Song Liu <>,
        "netdev\" <>,
        "bpf\" <>,
        "linux-kernel\" <>,
        Jesper Dangaard Brouer <>
Subject: Re: [PATCH] bpf: validate bpf_func when BPF_JIT is enabled

Sami Tolvanen <> writes:

> On Wed, Sep 11, 2019 at 5:09 AM Toke Høiland-Jørgensen <> wrote:
>> Björn Töpel <> writes:
>> > I ran the "xdp_rxq_info" sample with and without Sami's patch:
>> Thanks for doing this!
> Yes, thanks for testing this Björn!
>> Or (1/22998700 - 1/23923874) * 10**9 == 1.7 nanoseconds of overhead.
>> I guess that is not *too* bad; but it's still chipping away at
>> performance; anything we could do to lower the overhead?
> The check is already rather minimal, but I could move this to a static
> inline function to help ensure the compiler doesn't generate an
> additional function call for this. I'm also fine with gating this
> behind a separate config option, but I'm not sure if that's worth it.
> Any thoughts?

I think it would be good if you do both. I'm a bit worried that XDP
performance will end up in a "death by a thousand paper cuts" situation,
so I'd rather push back on even relatively small overheads like this; so
being able to turn it off in the config would be good.

Can you share more details about what the "future CFI checking" is
likely to look like?


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