linux-kernel - Re: [PATCH bpf-next v3 0/3] bpf: Add LDX/STX/ST sanitize in jited BPF progs

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Message-ID: <20221128003800.h2bmqcv5dfqmfbcf@MacBook-Pro-5.local>
Date:   Sun, 27 Nov 2022 16:38:00 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Hao Sun <sunhao.th@...il.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        john.fastabend@...il.com, andrii@...nel.org, martin.lau@...ux.dev,
        song@...nel.org, yhs@...com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, davem@...emloft.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 0/3] bpf: Add LDX/STX/ST sanitize in jited
 BPF progs

On Fri, Nov 25, 2022 at 08:29:09PM +0800, Hao Sun wrote:
> The verifier sometimes makes mistakes[1][2] that may be exploited to
> achieve arbitrary read/write. Currently, syzbot is continuously testing
> bpf, and can find memory issues in bpf syscalls, but it can hardly find
> mischecking/bugs in the verifier. We need runtime checks like KASAN in
> BPF programs for this. This patch series implements address sanitize
> in jited BPF progs for testing purpose, so that tools like syzbot can
> find interesting bugs in the verifier automatically by, if possible,
> generating and executing BPF programs that bypass the verifier but have
> memory issues, then triggering this sanitizing.

The above paragraph makes it sound that it's currently impossible to
use kasan with BPF. Which is confusing and incorrect statement.
kasan adds all the necessary instrumentation to BPF interpreter already
and syzbot can perform bug discovery.
syzbot runner should just disable JIT and run all progs via interpreter.
Adding all this logic to run JITed progs in kasan kernel is
just unnecessary complexity.