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

[Pavel Machek <pavel@denx.de>]

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@google.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@ucw.cz>

-- 
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