linux-kernel - Re: Sanitize CPU-state when switching tasks (was sanitize CPU-state when switching from virtual-8086 mode to other task)

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Message-ID: <52CF573F.8030300@zytor.com>
Date:	Thu, 09 Jan 2014 18:13:19 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>
CC:	halfdog <me@...fdog.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ben Hutchings <ben@...adent.org.uk>
Subject: Re: Sanitize CPU-state when switching tasks (was sanitize CPU-state
 when switching from virtual-8086 mode to other task)

On 01/09/2014 04:42 PM, Linus Torvalds wrote:
> On Fri, Jan 10, 2014 at 6:58 AM, Borislav Petkov <bp@...en8.de> wrote:
>>
>> Ok, I was able to reproduce
> 
> Looking at this, I think this is just a bug in our
> restore_fpu_checking() hackery for X86_FEATURE_FXSAVE_LEAK..
> 
> Which also explains why it only triggers on E-350 - it's only relevant
> for those K7/K8 CPU's that use this.
> 
> Maybe just add a fcnlex to before the emms? Something like this
> (TOTALLY UNTESTED!!) attached patch.
> 

OK, that sounds very reasonable.  Boris, halfdog, does something like
this resolve your problem?

	-hpa


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