From nobody Wed Oct 1 23:27:56 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7F19F2C2376; Sun, 28 Sep 2025 11:07:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759057651; cv=none; b=L/FCJIAW9NC/UQ8fAshUnzAD5zozCWqzpdh3MEQbqEWf2a2SqELCb7lhQS2hTWfBKDZFlXSWP2/9CxQLSvHTO4eOJ4N7KmyBPTUtJOur1SlNgPfnWSPIFWP30da12mKiZRE+FIKoDVs5L7mTQMevSCY2ZDP6rNjylMwdwuVdciU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759057651; c=relaxed/simple; bh=FH2sTDQJhpTphvaX4szRy8f0pnudRzvD6RNhp4vVOyE=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=XGtBO7Kn3kh/deviY0mdRtQ9xxv1bLogIQd5iNIbdlcTB4tdqUh3JvxJW5sPDJMpJ0L1/p/keDDaH1+m2aKjAKAQJCAEpouUINmI3uoUf8JkSt0+Y9o38cnyh7wY8plfVzr9BV7w8uCm0wN8w6Ueq/4IEb7lX8C7VEgkKaJ/Mdk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IUn7rIAF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IUn7rIAF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 16977C19422; Sun, 28 Sep 2025 11:07:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759057651; bh=FH2sTDQJhpTphvaX4szRy8f0pnudRzvD6RNhp4vVOyE=; h=Date:From:To:Cc:Subject:References:From; b=IUn7rIAFypO58pGw0RWD9/heiJoxLdpdO4mpxAfEPnjXSZYy8t0s3Mp4NOpfd6PI8 bRiT2SmpVgQUlq4b7Gx/SGXIhGkxrMaHRl2OTdSBpRkQqxpuGm5DW+m9AJkdRdDjuJ VLeLhBOCK9MjiUiQQebio7mTMqMjeFXN6KsQCxDBGmWdozSNO43cx77XKpVrSOzMPn 4n/QlBuBVkJUHSDOoF0g+fswiuxV897iKwnFQsg+rtOw4jWEf5HdQq8I3nyW2WEV3Y f/72Xx1rwF3vc/DAiOz0Ao9oIOlfjgZtellQSs8I9UFVjC6dGt0dFZByfAncjx9rhj 6xv8n7/SZ5Pmw== Received: from rostedt by gandalf with local (Exim 4.98.2) (envelope-from ) id 1v2pH4-0000000D8Ot-0N9g; Sun, 28 Sep 2025 07:09:02 -0400 Message-ID: <20250928110901.942338034@kernel.org> User-Agent: quilt/0.68 Date: Sun, 28 Sep 2025 07:08:35 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Wang Liang , Menglong Dong , stable@vger.kernel.org, Peter Zijlstra , Jiri Olsa Subject: [for-linus][PATCH 3/3] tracing: fgraph: Protect return handler from recursion loop References: <20250928110832.098564441@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Masami Hiramatsu (Google)" function_graph_enter_regs() prevents itself from recursion by ftrace_test_recursion_trylock(), but __ftrace_return_to_handler(), which is called at the exit, does not prevent such recursion. Therefore, while it can prevent recursive calls from fgraph_ops::entryfunc(), it is not able to prevent recursive calls to fgraph from fgraph_ops::retfunc(), resulting in a recursive loop. This can lead an unexpected recursion bug reported by Menglong. is_endbr() is called in __ftrace_return_to_handler -> fprobe_return -> kprobe_multi_link_exit_handler -> is_endbr. To fix this issue, acquire ftrace_test_recursion_trylock() in the __ftrace_return_to_handler() after unwind the shadow stack to mark this section must prevent recursive call of fgraph inside user-defined fgraph_ops::retfunc(). This is essentially a fix to commit 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer"), because before that fgraph was only used from the function graph tracer. Fprobe allowed user to run any callbacks from fgraph after that commit. Reported-by: Menglong Dong Closes: https://lore.kernel.org/all/20250918120939.1706585-1-dongml2@chinat= elecom.cn/ Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer") Cc: stable@vger.kernel.org Cc: Peter Zijlstra Link: https://lore.kernel.org/175852292275.307379.9040117316112640553.stgit= @devnote2 Signed-off-by: Masami Hiramatsu (Google) Acked-by: Jiri Olsa Tested-by: Menglong Dong Acked-by: Menglong Dong Signed-off-by: Steven Rostedt (Google) --- kernel/trace/fgraph.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c index 1e3b32b1e82c..484ad7a18463 100644 --- a/kernel/trace/fgraph.c +++ b/kernel/trace/fgraph.c @@ -815,6 +815,7 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, u= nsigned long frame_pointe unsigned long bitmap; unsigned long ret; int offset; + int bit; int i; =20 ret_stack =3D ftrace_pop_return_trace(&trace, &ret, frame_pointer, &offse= t); @@ -829,6 +830,15 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, = unsigned long frame_pointe if (fregs) ftrace_regs_set_instruction_pointer(fregs, ret); =20 + bit =3D ftrace_test_recursion_trylock(trace.func, ret); + /* + * This can fail because ftrace_test_recursion_trylock() allows one nest + * call. If we are already in a nested call, then we don't probe this and + * just return the original return address. + */ + if (unlikely(bit < 0)) + goto out; + #ifdef CONFIG_FUNCTION_GRAPH_RETVAL trace.retval =3D ftrace_regs_get_return_value(fregs); #endif @@ -852,6 +862,8 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, u= nsigned long frame_pointe } } =20 + ftrace_test_recursion_unlock(bit); +out: /* * The ftrace_graph_return() may still access the current * ret_stack structure, we need to make sure the update of --=20 2.50.1