linux-kernel - Re: [PATCH] intel_txt: add s3 userspace memory integrity verification

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Date:	Fri, 04 Dec 2009 09:53:37 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	"Cihula, Joseph" <joseph.cihula@...el.com>,
	Pavel Machek <pavel@....cz>,
	"Wang, Shane" <shane.wang@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"chrisw@...s-sol.org" <chrisw@...s-sol.org>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"jbeulich@...ell.com" <jbeulich@...ell.com>,
	"peterm@...hat.com" <peterm@...hat.com>
Subject: Re: [PATCH] intel_txt: add s3 userspace memory integrity verification

On 12/04/2009 09:13 AM, Andi Kleen wrote:
>>>
>>> So no, you did not audit do_suspend_lowlevel to make sure it does not
>>> follow function pointers. Bad.
>>
>> We aren't aware of any code or data used by the resume path that is outside of the tboot-MAC'ed regions above--if you can point out any then we will gladly address them.
> 
> Code coverage is not enough, you need data coverage too.  If someone 
> modifies kernel data it's typically easy to subvert code as a next step.
> 

The only function pointers that are invoked on the do_suspend_lowlevel
path are some paravirt_crap pointers, but those are located inside
kernel static data.

This is not to say that this isn't a new constraint, and should be
documented, and checked ahead of time...

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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