Re: [PATCH v2] tracing: fix CFI violation in probestub test

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

On Tue,  2 Jun 2026 16:54:08 +0300
Eva Kurchatova <eva.kurchatova@virtuozzo.com> wrote:

> When multiple callbacks are registered on the same tracepoint,
> callbacks will be indirectly called via traceiter helper.
> 
> Pointers to __probestub_* callbacks reside in __tracepoints section,
> which is excluded from ENDBR checks in objtool, causing objtool to
> assume those functions are never indirectly called.
> 
> Registering multiple callbacks using sched_wakeup test will result
> in #CP exception due to missing ENDBR in __probestub_sched_wakeup
> on a CFI-enabled machine.
> 
> Fix this by adding CFI_NOSEAL annotation to probestub declaration.
> 

Thanks, this looks good to me.

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

> Fixes: d5173f753750 ("objtool: Exclude __tracepoints data from ENDBR checks")
> Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
> ---
>  include/linux/tracepoint.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 763eea4d80d8..38e9f49a71b7 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -20,6 +20,7 @@
>  #include <linux/rcupdate_trace.h>
>  #include <linux/tracepoint-defs.h>
>  #include <linux/static_call.h>
> +#include <asm/cfi.h>
>  
>  struct module;
>  struct tracepoint;
> @@ -389,6 +390,13 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  	void __probestub_##_name(void *__data, proto)			\
>  	{								\
>  	}								\
> +	/*								\
> +	 * Annotate the probestub 'CFI_NOSEAL' to stop objtool from	\
> +	 * requesting the kernel remove the ENDBR, because the only	\
> +	 * references to the function are in the __tracepoint section,	\
> +	 * that objtool doesn't scan.					\
> +	 */								\
> +	CFI_NOSEAL(__probestub_##_name);				\
>  	DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);	\
>  	DEFINE_RUST_DO_TRACE(_name, TP_PROTO(proto), TP_ARGS(args))
>  
> -- 
> 2.54.0
> 


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