linux-kernel - Re: [patch V4 part 2 03/18] x86/entry: Mark enter_from_user

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Message-Id: <20200508172100.38fa5eec6b0d6047c841b030@kernel.org>
Date:   Fri, 8 May 2020 17:21:00 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 2 03/18] x86/entry: Mark enter_from_user_mode()
 noinstr

On Tue, 05 May 2020 15:41:15 +0200
Thomas Gleixner <tglx@...utronix.de> 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 noinstr which moves it into the instrumentation protected text
> section and includes notrace.
> 
> Note, this needs further fixups in context tracking to ensure that the
> full call chain is protected. Will be addressed in follow up changes.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

Thank you,

> ---
>  arch/x86/entry/common.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -41,7 +41,7 @@
>  
>  #ifdef CONFIG_CONTEXT_TRACKING
>  /* Called on entry from user mode with IRQs off. */
> -__visible inline void enter_from_user_mode(void)
> +__visible inline noinstr void enter_from_user_mode(void)
>  {
>  	CT_WARN_ON(ct_state() != CONTEXT_USER);
>  	user_exit_irqoff();
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>