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Re: [Xen-devel] Xen 4.0.0x allows for data corruption in Dom0

To: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Subject: Re: [Xen-devel] Xen 4.0.0x allows for data corruption in Dom0
From: Joanna Rutkowska <joanna@xxxxxxxxxxxxxxxxxxxxxx>
Date: Tue, 09 Mar 2010 00:56:22 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
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On 03/09/2010 12:52 AM, Daniel Stodden wrote:
> On Mon, 2010-03-08 at 18:30 -0500, Joanna Rutkowska wrote:
>> On 03/09/2010 12:22 AM, Daniel Stodden wrote:
>>> On Sun, 2010-03-07 at 11:12 -0500, Pasi Kärkkäinen wrote:
>>>> On Sun, Mar 07, 2010 at 02:39:09PM +0000, Keir Fraser wrote:
>>>>> On 07/03/2010 14:36, "Pasi Kärkkäinen" <pasik@xxxxxx> wrote:
>>>>>>> Tried a few times and no luck reproducing so far. I hope some other 
>>>>>>> people
>>>>>>> on the list also will give it a go, since it's so easy to try it out.
>>>>>> I'm able to reproduce this with xen/master dom0 kernel (from
>>>>>> 2010-02-20),
>>>>>> but I'm not able to reproduce it with the current xen/stable
>>>>>> I'll try with the most recent dom0 kernel aswell..
>>>>> Thanks Pasi!
>>>> It seems to happen with the latest xen/master aswell!
>>> Does this look to you like we're corrupting memory or on-disk storage?
>>> E.g. does a
>>> $ dd if=/dev/zero bs=1M | hexdump -C 
>>> have the same issue?
>> I think there might be a chance that the above executes correctly, even
>> if we have memory corruption -- this might be e.g. because the actual
>> "dest" buffer here would be much smaller than the fs cache buffer used
>> when we copy onto disk. And so our small dest buffer might just not be
>> so likely to be hit with this presumably random corruption.
>> Perhaps dd'ing onto /dev/shm would be a better way to check this?
> I agree that a negative doesn't mean much. I'm just poking around there
> because the positive would have mattered: If we still get to see it,
> we're out of the storage discussion and can focus on memory corruption.

If you're thinking about a potential Dom0 disk-driver problem, then I
think we can rule this out. This is because I have tried this on both
encrypted and non-encrypted filesystems, but the pattern of corruptions
was exactly the same. If the disk driver was feeding LUKS (the crypto
driver) with a wrong data, the corruptions would definitely look

I also tried ext4 and ext3 filesystems, but same results.


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