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

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Message-ID: <alpine.LNX.2.00.1608120800100.22028@cbobk.fhfr.pm>
Date:	Fri, 12 Aug 2016 08:01:31 +0200 (CEST)
From:	Jiri Kosina <jikos@...nel.org>
To:	Thomas Garnier <thgarnie@...gle.com>
cc:	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	keescook@...omium.org, kernel-hardening@...ts.openwall.com,
	bpetkov@...e.de, yinghai@...nel.org
Subject: Re: [PATCH v1] x86/power/64: Restore processor state before using
 per-cpu variables

On Thu, 11 Aug 2016, Thomas Garnier wrote:

> 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>

Alright, this did the trick, thanks :) Feel free to add

	Reported-by: Jiri Kosina <jkosina@...e.cz>
	Tested-by: Jiri Kosina <jkosina@...e.cz>

One thing is still beyond me though ... how the heck this doesn't happen 
without DEBUG_LOCK_ALLOC? The percpu area pointer should be corrupted 
nevertheless, shouldn't it?

Thanks,

-- 
Jiri Kosina
SUSE Labs