linux-kernel - Re: [patch part-II V2 02/13] x86/entry: Mark enter_from_user

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Date:   Tue, 10 Mar 2020 11:15:37 +0100
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [patch part-II V2 02/13] x86/entry: Mark enter_from_user_mode()
 notrace and NOKPROBE



On 3/8/20 11:24 PM, Thomas Gleixner wrote:
> Both the callers in the low level ASM code and __context_tracking_exit()
> which is invoked from enter_from_user_mode() via user_exit_irqoff() are
> marked NOKPROBE. Allowing enter_from_user_mode() to be probed is
> inconsistent at best.
> 
> Aside of that while function tracing per se is safe the function trace
> entry/exit points can be used via BPF as well which is not safe to use
> before context tracking has reached CONTEXT_KERNEL and adjusted RCU.
> 
> Mark it notrace and NOKROBE.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>   arch/x86/entry/common.c |    3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)


Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>

alex.

> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -40,11 +40,12 @@
>   
>   #ifdef CONFIG_CONTEXT_TRACKING
>   /* Called on entry from user mode with IRQs off. */
> -__visible inline void enter_from_user_mode(void)
> +__visible inline notrace void enter_from_user_mode(void)
>   {
>   	CT_WARN_ON(ct_state() != CONTEXT_USER);
>   	user_exit_irqoff();
>   }
> +NOKPROBE_SYMBOL(enter_from_user_mode);
>   #else
>   static inline void enter_from_user_mode(void) {}
>   #endif
>