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

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Message-ID: <20241127111020.1738105-1-elver@google.com>
Date: Wed, 27 Nov 2024 12:10:00 +0100
From: Marco Elver <elver@...gle.com>
To: elver@...gle.com, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, 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: [PATCH bpf-next v2 1/2] bpf: Remove bpf_probe_write_user() warning message

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>
---
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