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

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Date:	Mon, 9 Mar 2015 09:30:50 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Mark Seaborn <mseaborn@...omium.org>
Cc:	Pavel Machek <pavel@....cz>,
	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, 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.)

--Andy
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