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Date: Thu, 13 Jun 2024 12:21:07 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>, Alexander Potapenko
 <glider@google.com>, Andrew Morton <akpm@linux-foundation.org>, Christoph
 Lameter <cl@linux.com>, David Rientjes <rientjes@google.com>, Heiko
 Carstens <hca@linux.ibm.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Marco
 Elver <elver@google.com>, Masami Hiramatsu <mhiramat@kernel.org>, Pekka
 Enberg <penberg@kernel.org>, Vasily Gorbik <gor@linux.ibm.com>, Vlastimil
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 kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
 linux-mm@kvack.org, linux-s390@vger.kernel.org,
 linux-trace-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
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 <svens@linux.ibm.com>
Subject: Re: [PATCH v4 01/35] ftrace: Unpoison ftrace_regs in
 ftrace_ops_list_func()
Message-ID: <20240613122107.6e9299eb@rorschach.local.home>
In-Reply-To: <20240613153924.961511-2-iii@linux.ibm.com>
References: <20240613153924.961511-1-iii@linux.ibm.com>
	<20240613153924.961511-2-iii@linux.ibm.com>
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On Thu, 13 Jun 2024 17:34:03 +0200
Ilya Leoshkevich <iii@linux.ibm.com> wrote:

> Architectures use assembly code to initialize ftrace_regs and call
> ftrace_ops_list_func(). Therefore, from the KMSAN's point of view,
> ftrace_regs is poisoned on ftrace_ops_list_func entry(). This causes
> KMSAN warnings when running the ftrace testsuite.
> 
> Fix by trusting the architecture-specific assembly code and always
> unpoisoning ftrace_regs in ftrace_ops_list_func.
> 
> The issue was not encountered on x86_64 so far only by accident:
> assembly-allocated ftrace_regs was overlapping a stale partially
> unpoisoned stack frame. Poisoning stack frames before returns [1]
> makes the issue appear on x86_64 as well.
> 
> [1] https://github.com/iii-i/llvm-project/commits/msan-poison-allocas-before-returning-2024-06-12/
> 
> Reviewed-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---

Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve

>  kernel/trace/ftrace.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 65208d3b5ed9..c35ad4362d71 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -7407,6 +7407,7 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
>  void arch_ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
>  			       struct ftrace_ops *op, struct ftrace_regs *fregs)
>  {
> +	kmsan_unpoison_memory(fregs, sizeof(*fregs));
>  	__ftrace_ops_list_func(ip, parent_ip, NULL, fregs);
>  }
>  #else