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

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Message-ID: <20091204201056.GB741@basil.fritz.box>
Date:	Fri, 4 Dec 2009 21:10:56 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"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 Fri, Dec 04, 2009 at 09:53:37AM -0800, H. Peter Anvin wrote:
> 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.

Was referring to panic(), like Pavel said.

It would be relatively easy to subvert something called by panic
that just jumps back to after the MAC checks.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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