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

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Date:	Fri, 4 Dec 2009 23:20:45 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Cihula, Joseph" <joseph.cihula@...el.com>
Cc:	"Wang, Shane" <shane.wang@...el.com>,
	"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>,
	Andi Kleen <andi@...stfloor.org>,
	"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>,
	"Brown, Len" <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH] intel_txt: add s3 userspace memory integrity
 verification

> > > +
> > > +   ret = tboot_pre_stack_switch();
> > > +   if (!ret) {
> > > +           tboot_switch_stack_call(tboot_do_suspend_lowlevel_call,
> > > +                                   (u64)new_stack_ptr);
> >
> > ...and here you add requirements to suspend_lowlevel that were not
> > there before. ("May not act on unchecksummed memory"), without
> > documenting them.
> 
> Really the only requirement is (as discussed in the previous thread) that it only use code and data within [_text, _end - _text]--do you think that this really needs to be called out?  do_suspend_lowlevel() is a very simple function that has just the one (resume path) call to another simple function--it doesn't seem likely that it would violate this.
> 

Resume code is already pretty tricky, and you add yet another layer of
trickery. Yes, it needs to be properly documented.

And... how does it interact with restore_processor_state? I don't
think do_suspend_lowlevel is as simple as you think...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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