Re: [PATCH v4 01/35] ftrace: Unpoison ftrace_regs in ftrace_ops_list_func()

[Steven Rostedt]

On Thu, 13 Jun 2024 17:34:03 +0200
Ilya Leoshkevich <iii@xxxxxxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> ---

Acked-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>

-- 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