linux-kernel - Re: DRAM unreliable under specific access patern

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Message-ID: <20150309211751.GA3991@amd>
Date:	Mon, 9 Mar 2015 22:17:51 +0100
From:	Pavel Machek <pavel@....cz>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Mark Seaborn <mseaborn@...omium.org>,
	kernel list <linux-kernel@...r.kernel.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Subject: Re: DRAM unreliable under specific access patern

On Mon 2015-03-09 09:30:50, Andy Lutomirski wrote:
> On Mon, Mar 9, 2015 at 9:03 AM, Mark Seaborn <mseaborn@...omium.org> wrote:
> > On 6 January 2015 at 15:20, Pavel Machek <pavel@....cz> wrote:
> >> On Mon 2015-01-05 19:23:29, One Thousand Gnomes wrote:
> >> > > In the meantime, I created test that actually uses physical memory,
> >> > > 8MB apart, as described in some footnote. It is attached. It should
> >> > > work, but it needs boot with specific config options and specific
> >> > > kernel parameters.
> >> >
> >> > Why not just use hugepages. You know the alignment guarantees for 1GB
> >> > pages and that means you don't even need to be root
> >> >
> >> > In fact - should we be disabling 1GB huge page support by default at this
> >> > point, at least on non ECC boxes ?
> >>
> >> Actually, I could not get my test code to run; and as code from
> >>
> >> https://github.com/mseaborn/rowhammer-test
> >>
> >> reproduces issue for me, I stopped trying. I could not get it to
> >> damage memory of other process than itself (but that should be
> >> possible), I guess that's next thing to try.
> >
> > FYI, rowhammer-induced bit flips do turn out to be exploitable.  Here
> > are the results of my research on this:
> > http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html
> >
> 
> IIRC non-temporal writes will force cachelines out to main memory
> *and* invalidate them.  (I wouldn't be shocked if Skylake changes
> this, but I'm reasonably confident that it's true on all currently
> available Intel chips.)
> 
> Have you checked whether read; read; nt store; nt store works?
> 
> (I can't test myself easily right now -- I think my laptop is too old
> for this issue.)

Well, if you had laptop with that issue, it would still be tricky to
test this. It takes a while to reproduce...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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