linux-kernel - Re: [PATCH bpf-next v4 1/2] bpf: Remove bpf_probe_write

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Message-ID: <89424046-1142-447e-8a63-d8492ccd9abc@iogearbox.net>
Date: Fri, 29 Nov 2024 17:35:57 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: Marco Elver <elver@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
 Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Nikola Grcevski <nikola.grcevski@...fana.com>,
 bpf@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 1/2] bpf: Remove bpf_probe_write_user()
 warning message

On 11/29/24 9:59 AM, Marco Elver wrote:
> The warning message for bpf_probe_write_user() was introduced in
> 96ae52279594 ("bpf: Add bpf_probe_write_user BPF helper to be called in
> tracers"), with the following in the commit message:
> 
>      Given this feature is meant for experiments, and it has a risk of
>      crashing the system, and running programs, we print a warning on
>      when a proglet that attempts to use this helper is installed,
>      along with the pid and process name.
> 
> After 8 years since 96ae52279594, bpf_probe_write_user() has found
> successful applications beyond experiments [1, 2], with no other good
> alternatives. Despite its intended purpose for "experiments", that
> doesn't stop Hyrum's law, and there are likely many more users depending
> on this helper: "[..] it does not matter what you promise [..] all
> observable behaviors of your system will be depended on by somebody."
> 
> The ominous "helper that may corrupt user memory!" has offered no real
> benefit, and has been found to lead to confusion where the system
> administrator is loading programs with valid use cases.
> 
> As such, remove the warning message.
> 
> Link: https://lore.kernel.org/lkml/20240404190146.1898103-1-elver@google.com/ [1]
> Link: https://lore.kernel.org/r/lkml/CAAn3qOUMD81-vxLLfep0H6rRd74ho2VaekdL4HjKq+Y1t9KdXQ@mail.gmail.com/ [2]
> Link: https://lore.kernel.org/all/CAEf4Bzb4D_=zuJrg3PawMOW3KqF8JvJm9SwF81_XHR2+u5hkUg@mail.gmail.com/
> Signed-off-by: Marco Elver <elver@...gle.com>
> Acked-by: Jiri Olsa <jolsa@...nel.org>

Acked-by: Daniel Borkmann <daniel@...earbox.net>