From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) (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 3F18A2F90E2 for ; Mon, 22 Sep 2025 08:01:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758528092; cv=none; b=CaRQ69d1K8ss3D7WeuxzK/dhYmrehgfXmyPjfm2hj77NUAWWtyWObQUFLk+4rwpWHC9e3u7spiIUAB8xRnNIFnlm441RR0RK6Z1Dm6uzmBXIHq08ymvf4xXxEm0Ze1n67kmWcFk6qG10N+qr1l69uV2KR8cWOqjax51gU+EyKHI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758528092; c=relaxed/simple; bh=tNlpG+9RSRfVOzhoE75w1gSvYEFTE68gc0kd3RJAPcg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=J/fc2lB3jIo584eR0sjIfyYUu692/lyURsbF4gDG9OPhhGh4zXbiP/KxXy6uC4QktryNoJkPzq1/bERqpSNtrnvzimYWtf4v43yNdzaSHDfjj9n8tbhh+vfAj8x8EYhIAno1iW/d9xAY5qPEa+rGPtw4WMd1lLEm7eh4OEVLwlE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=eJaUQL+9; arc=none smtp.client-ip=95.215.58.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="eJaUQL+9" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758528087; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QB4wVTq4PE7QI4UvE98apEAlUKHfwg3wd7rVHhsBMbY=; b=eJaUQL+9BgZzluZAZg8wV5hZSO+oWVE+XDJ6vISKAFmAYMDSfMLZC97pU9A4gliWWoMrzJ wDFcmbzFF0CHZFAr3NGbPcQHS0M4KMZa5k/l/qA0Zuyli6j3+6iPgUU+bYhH7p2CsnhSeP Ciu56xGlxBkF2WsCHl7yuhEMRtARvTY= From: menglong.dong@linux.dev To: "Masami Hiramatsu (Google)" Cc: Peter Zijlstra , Steven Rostedt , 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 v2 1/2] tracing: fgraph: Protect return handler from recursion loop Date: Mon, 22 Sep 2025 16:01:17 +0800 Message-ID: <3373807.aeNJFYEL58@7940hx> In-Reply-To: <175852292275.307379.9040117316112640553.stgit@devnote2> References: <175852291163.307379.14414635977719513326.stgit@devnote2> <175852292275.307379.9040117316112640553.stgit@devnote2> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" X-Migadu-Flow: FLOW_OUT On 2025/9/22 14:35 Masami Hiramatsu (Google) write: > 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@chinatelecom.cn/ > Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer") > Cc: stable@vger.kernel.org > Signed-off-by: Masami Hiramatsu (Google) > Acked-by: Jiri Olsa > --- > Changes in v2: > - Do not warn on failing ftrace_test_recursion_trylock() because it > allows one-level nest. > --- > 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, unsigned long frame_pointe > unsigned long bitmap; > unsigned long ret; > int offset; > + int bit; > int i; The bpf bench testings work fine on this version :) Tested-by: Menglong Dong Acked-by: Menglong Dong Thanks! Menglong Dong > > ret_stack = ftrace_pop_return_trace(&trace, &ret, frame_pointer, &offset); > @@ -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); > > + bit = 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 = ftrace_regs_get_return_value(fregs); > #endif > @@ -852,6 +862,8 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, unsigned long frame_pointe > } > } > > + 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 > > >