linux-kernel - Re: [PATCH bpf-next v2 1/2] bpf: Remove bpf_probe_write

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Message-ID: <Z0cHTRsJoWgZBGNU@krava>
Date: Wed, 27 Nov 2024 12:49:33 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Marco Elver <elver@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	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>,
	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 v2 1/2] bpf: Remove bpf_probe_write_user()
 warning message

On Wed, Nov 27, 2024 at 12:10:00PM +0100, 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>

jirka

> ---
> v2:
> * Just delete the message entirely (suggested by Andrii Nakryiko)
> ---
>  kernel/trace/bpf_trace.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 630b763e5240..0ab56af2e298 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -362,9 +362,6 @@ static const struct bpf_func_proto *bpf_get_probe_write_proto(void)
>  	if (!capable(CAP_SYS_ADMIN))
>  		return NULL;
>  
> -	pr_warn_ratelimited("%s[%d] is installing a program with bpf_probe_write_user helper that may corrupt user memory!",
> -			    current->comm, task_pid_nr(current));
> -
>  	return &bpf_probe_write_user_proto;
>  }
>  
> -- 
> 2.47.0.338.g60cca15819-goog
>