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From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: Menglong Dong <menglong8.dong@gmail.com>
Cc: peterz@infradead.org, jolsa@kernel.org, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
	x86@kernel.org, hpa@zytor.com, kees@kernel.org,
	samitolvanen@google.com, rppt@kernel.org, luto@kernel.org,
	mhiramat@kernel.org, ast@kernel.org, andrii@kernel.org,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH] x86/ibt: make is_endbr() notrace
Date: Fri, 19 Sep 2025 17:52:55 +0900	[thread overview]
Message-ID: <20250919175255.f7c2c77fa03665a42b148046@kernel.org> (raw)
In-Reply-To: <20250918120939.1706585-1-dongml2@chinatelecom.cn>

On Thu, 18 Sep 2025 20:09:39 +0800
Menglong Dong <menglong8.dong@gmail.com> wrote:

> is_endbr() is called in __ftrace_return_to_handler -> fprobe_return ->
> kprobe_multi_link_exit_handler -> is_endbr.
> 
> It is not protected by the "bpf_prog_active", so it can't be traced by
> kprobe-multi, which can cause recurring and panic the kernel. Fix it by
> make it notrace.

Ah, OK. This is fprobe's issue. fprobe depends on fgraph to check
recursion, but fgraph only detects the recursion in the entry handler.
Thus it happens in the exit handler, fprobe does not check the recursion.

But since the fprobe provides users to register callback at exit, it
should check the recursion in return path too.

Thanks,

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

  parent reply	other threads:[~2025-09-19  8:53 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-09-18 12:09 [PATCH] x86/ibt: make is_endbr() notrace Menglong Dong
2025-09-18 13:05 ` Peter Zijlstra
2025-09-18 13:32   ` Menglong Dong
2025-09-18 16:02     ` Alexei Starovoitov
2025-09-18 16:59       ` Peter Zijlstra
2025-09-18 17:53         ` Alexei Starovoitov
2025-09-19  1:13           ` Menglong Dong
2025-09-22  6:52             ` Peter Zijlstra
2025-09-22  7:13               ` menglong.dong
2025-09-22  7:19                 ` Peter Zijlstra
2025-09-22  7:21                   ` Menglong Dong
2025-09-22  6:36           ` Peter Zijlstra
2025-09-18 16:56     ` Peter Zijlstra
2025-09-19 12:35       ` Masami Hiramatsu
2025-09-19  8:52 ` Masami Hiramatsu [this message]
2025-09-19  8:58   ` Menglong Dong
2025-09-19 12:32     ` Masami Hiramatsu
2025-09-19 11:57 ` [PATCH] tracing: fgraph: Protect return handler from recursion loop Masami Hiramatsu (Google)
2025-09-19 15:27   ` Steven Rostedt
2025-09-20  7:45     ` Jiri Olsa
2025-09-22  6:16       ` Masami Hiramatsu
2025-09-22 13:38         ` Jiri Olsa
2025-09-22 14:42           ` Steven Rostedt
2025-09-22 19:45           ` Jiri Olsa
2025-09-21  4:05     ` Masami Hiramatsu
2025-09-21 22:52       ` Steven Rostedt
2025-09-24 22:58         ` Masami Hiramatsu
2025-09-20 13:39   ` Menglong Dong
2025-09-21  4:06     ` Masami Hiramatsu
2025-09-21 23:00       ` Steven Rostedt
2025-09-24 22:59         ` Masami Hiramatsu
2025-09-22  5:19     ` Masami Hiramatsu

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