netdev - Re: [PATCH v2 0/4] Fix up bpf_jit

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Message-ID: <CACAyw99FGc_z2zXjrjP=0k3jz0vz2u6ddiGVbzD0zuTcTU4rzg@mail.gmail.com>
Date:   Thu, 14 Oct 2021 15:22:26 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Jakub Sitnicki <jakub@...udflare.com>
Cc:     Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Luke Nelson <luke.r.nels@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        kernel-team <kernel-team@...udflare.com>,
        linux-riscv@...ts.infradead.org,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] Fix up bpf_jit_limit some more

On Wed, 13 Oct 2021 at 20:56, Jakub Sitnicki <jakub@...udflare.com> wrote:
>
> On Tue, Oct 12, 2021 at 03:59 PM CEST, Lorenz Bauer wrote:
> > Some more cleanups around bpf_jit_limit to make it readable via sysctl.
> >
> > Jakub raised the point that a sysctl toggle is UAPI and therefore
> > can't be easily changed later on. I tried to find another place to stick
> > the info, but couldn't find a good one. All the current BPF knobs are in
> > sysctl.
> >
> > There are examples of read only sysctls:
> > $ sudo find /proc/sys -perm 0444 | wc -l
> > 90
> >
> > There are no examples of sysctls with mode 0400 however:
> > $ sudo find /proc/sys -perm 0400 | wc -l
> > 0
> >
> > Thoughts?
>
> I threw this idea out there during LPC already, that it would be cool to
> use BPF iterators for that. Pinned/preloaded iterators were made for
> dumping kernel data on demand after all.
>
> What is missing is a BPF iterator type that would run the program just
> once (there is just one thing to print), and a BPF helper to lookup
> symbol's address.
>
> I thought this would require a bit of work, but actually getting a PoC
> (see below) to work was rather pleasntly straightforward.
>
> Perhaps a bit of a hack but I'd consider it as an alternative.

I spoke to Jakub, I won't have time to work on this myself. So I'll
drop this patch from the series and send a v3 with just the fixes to
bpf_jit_limit.

-- 
Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK

www.cloudflare.com