linux-kernel - Re: [TuxOnIce-devel] RFC: Suspend-to-ram cold boot protection by encrypting page cache

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Message-ID: <20090711221039.GC1670@ucw.cz>
Date:	Sun, 12 Jul 2009 00:10:39 +0200
From:	Pavel Machek <pavel@....cz>
To:	Jeremy Maitin-Shepard <jeremy@...emyms.com>
Cc:	Nigel Cunningham <ncunningham@...a.org.au>,
	tuxonice-devel@...ts.tuxonice.net, linux-kernel@...r.kernel.org,
	Rafael Wysocki <rjw@...k.pl>
Subject: Re: [TuxOnIce-devel] RFC: Suspend-to-ram cold boot protection by
	encrypting page cache

On Fri 2009-07-10 00:05:23, Jeremy Maitin-Shepard wrote:
> Pavel Machek <pavel@....cz> writes:
> 
> > On Wed 2009-07-08 04:09:41, Jeremy Maitin-Shepard wrote:
> >> Pavel Machek <pavel@....cz> writes:
> >> 
> >> > On Wed 2009-07-08 03:47:53, Jeremy Maitin-Shepard wrote:
> >> >> Pavel Machek <pavel@....cz> writes:
> >> >> 
> >> >> [snip]
> >> >> 
> >> >> > I believe uswsusp could be used rather easily. Just modify s2disk to
> >> >> > encrypt image in ram without writing it out, then decrypt it from ram
> >> >> > and resume... it should be interesting hack.
> >> >> 
> >> >> As far as I understand, that would be completely useless since the image
> >> >> that would be encrypted would just be a copy of what would still remain
> >> >> in memory.
> >> 
> >> > Yes... so next step would be kernel call that would erase all the
> >> > pagecache and anonymous pages. You would still leave some data in
> >> > kernel structures, but that would be quite hard to fix. 
> >> 
> >> Okay.  (This does still require the same assumption as TuxOnIce
> >> regarding the page cache, though.)
> 
> > (Not sure; clearing the page cache could be done atomically, from
> > interrupts disabled. But I'm no mm expert.)
> 
> But surely it wouldn't work to leave interrupts disabled after that
> until the page cache is restored.  After the page cache (and other
> sensitive memory) is encrypted, after possibly entering and resuming
> from S3, the page cache needs to be decrypted.  Userspace will be
> doing

I see no need for that. You'd do something like 'kill -9 -1; echo 3 >
drop_caches' after snapshot, then scrub free ram. At that point you
should have no sensitive data in the memory, and encrypted image you
can restore.

(Now, kill -9 -1 with frozen tasks may be tricky to implement....)
									Pavel

-- 
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