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

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Message-ID: <CALCETrXpJ7CPAKeh9nLA=PoCBT8w8NfhZg5cgUyG9BUtp2Jv+w@mail.gmail.com>
Date:	Mon, 5 Jan 2015 18:26:07 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
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 5, 2015 at 6:18 PM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> 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.
>

The vdso and the vvar page are both at probably-well-known physical
addresses, so you can at least target the kernel a little bit.  I
*think* that kASLR helps a little bit here.

--Andy

> --
>  Kirill A. Shutemov



-- 
Andy Lutomirski
AMA Capital Management, LLC
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