linux-kernel - Re: [syzbot] [bpf?] KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array

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Message-ID: <4980327b-698d-5c1a-42ab-327dc6a47515@iogearbox.net>
Date:   Tue, 29 Aug 2023 22:54:54 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Marco Elver <elver@...gle.com>
Cc:     yonghong.song@...ux.dev,
        syzbot <syzbot+97522333291430dd277f@...kaller.appspotmail.com>,
        andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
        haoluo@...gle.com, john.fastabend@...il.com, jolsa@...nel.org,
        kpsingh@...nel.org, linux-kernel@...r.kernel.org,
        martin.lau@...ux.dev, sdf@...gle.com, song@...nel.org,
        syzkaller-bugs@...glegroups.com, yhs@...com,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [syzbot] [bpf?] KCSAN: data-race in bpf_percpu_array_update /
 bpf_percpu_array_update (2)

On 8/29/23 10:36 PM, Marco Elver wrote:
[...]
> In this case, maybe data_race(*ldst++ = *lsrc++) would be more
> appropriate and efficient. Unlikely that READ_ONCE()/WRITE_ONCE() here
> helps make this any safer, i.e. the memcpy is still not atomic and if
> it's a bug on the user's side, it'll corrupt data either way.

I wasn't aware of data_race(), thanks for the suggestion! Just flushed out
a small patch.

Thanks,
Daniel