linux-kernel - Re: [PATCH v1] x86/power/64: Restore processor state before using per-cpu variables

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Message-ID: <20160812062919.GC30992@amd>
Date:	Fri, 12 Aug 2016 08:29:19 +0200
From:	Pavel Machek <pavel@...x.de>
To:	Thomas Garnier <thgarnie@...gle.com>
Cc:	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, keescook@...omium.org,
	kernel-hardening@...ts.openwall.com, jikos@...nel.org,
	bpetkov@...e.de, yinghai@...nel.org
Subject: Re: [PATCH v1] x86/power/64: Restore processor state before using
 per-cpu variables

Hi!

> Restore the processor state before calling any other function to ensure
> per-cpu variables can be used with KASLR memory randomization.
> 
> Tracing functions use per-cpu variables (gs based) and one was called
> just before restoring the processor state fully. It resulted in a double
> fault when both the tracing & the exception handler functions tried to
> use a per-cpu variable.
> 
> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
> ---
> Based on next-20160808
> 
> Thanks to Rafael, Jiri & Borislav in tracking down this bug.
> ---
>  kernel/power/hibernate.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index a881c6a..33c79b6 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -300,12 +300,12 @@ static int create_image(int platform_mode)
>  	save_processor_state();
>  	trace_suspend_resume(TPS("machine_suspend"), PM_EVENT_HIBERNATE, true);
>  	error = swsusp_arch_suspend();
> +	/* Restore control flow magically appears here */
> +	restore_processor_state();
>  	trace_suspend_resume(TPS("machine_suspend"), PM_EVENT_HIBERNATE, false);
>  	if (error)
>  		printk(KERN_ERR "PM: Error %d creating hibernation image\n",
>  			error);
> -	/* Restore control flow magically appears here */
> -	restore_processor_state();
>  	if (!in_suspend)
>  		events_check_enabled = false;
>  

Ugh. Plus it also fixes very confusing situation where /* Restore
control flow magically appears here */ comment was 4 lines away from
where it _actually_ magically appeared. Good catch.

Acked-by: Pavel Machek <pavel@....cz>

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html