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

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Message-ID: <20150106021836.GA24121@node.dhcp.inet.fi>
Date:	Tue, 6 Jan 2015 04:18:36 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@....cz>,
	Mark Seaborn <mseaborn@...omium.org>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: DRAM unreliable under specific access patern

On Mon, Jan 05, 2015 at 05:57:24PM -0800, Andy Lutomirski wrote:
> On Mon, Jan 5, 2015 at 5:47 PM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> > On Mon, Jan 05, 2015 at 11:50:04AM -0800, Andy Lutomirski wrote:
> >> On Mon, Jan 5, 2015 at 11:23 AM, One Thousand Gnomes
> >> <gnomes@...rguk.ukuu.org.uk> 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 ?
> >>
> >> Can you actually damage anyone else's data using a 1 GB hugepage?
> >
> > hugetlbfs is a filesystem: the answer is yes. Although I don't see the
> > issue as a big attach vector.
> 
> What I mean is: if I map a 1 GB hugepage and rowhammer it, is it
> likely that the corruption will be confined to the same 1 GB?

I don't know for sure, but it looks likely to me according to claim in the
paper (8MB). But it still can be sombody else's data: 644 file on
hugetlbfs mmap()ed r/o by anyone.

When I read the paper I thought that vdso would be interesting target for
the attack, but having all these constrains in place, it's hard aim the
attack anything widely used.

-- 
 Kirill A. Shutemov
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