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

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Message-ID: <20091204200933.GA741@basil.fritz.box>
Date:	Fri, 4 Dec 2009 21:09:33 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Cihula, Joseph" <joseph.cihula@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>, 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>, "H. Peter Anvin" <hpa@...or.com>,
	"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 09:41:24AM -0800, Cihula, Joseph wrote:
> > From: Andi Kleen [mailto:andi@...stfloor.org]
> > Sent: Friday, December 04, 2009 9:14 AM
> >
> > > "bad stuff" would be the execution of any code (or use of any data that affects execution)
> > that was not verified by tboot.  As long as panic() is within the code ranges MAC'ed by tboot
> > (see above), it would be covered.  Do you know of some panic() code paths that are outside of
> > this?
> >
> > Not code path, but the code called by panic (console drivers, debuggers etc.)
> > can well use data that is stored >4GB
> >
> > This can include structures with indirect pointers, like notifier chains.
> >
> > Notifier chains have a special checker than can check
> > for <4GB, but there are other call vectors too.
> 
> Since, as you pointed out in a previous email, it is doubtful that there will be any user-visible output at this point, we can change this path to a tboot reset (which will give us some serial output at least).  Is it going to be similarly unsafe to do a printk()?

Yes printk is similarly unsafe. It calls all the console machinery,
which has a lot of data.

Perhaps early_printk(), that is relatively self contained, but doesn't
always work.

Of course you would need to have a timeout before reset, and at this point the
delay loops are not calibrated yet, so you don't know how to wait.

-Andi

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