linux-kernel - Re: [Xen-devel] [PATCH] xen: Fix possible user space selector corruption

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Date:	Fri, 4 Oct 2013 14:33:53 +0100
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Frediano Ziglio <frediano.ziglio@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen: Fix possible user space selector corruption

On 04/10/13 14:20, Konrad Rzeszutek Wilk wrote:
> On Thu, Oct 03, 2013 at 01:51:32PM +0100, Frediano Ziglio wrote:
>> On Thu, 2013-10-03 at 11:04 +0100, Andrew Cooper wrote:
>>> On 03/10/13 09:24, Frediano Ziglio wrote:
>>>>
>>>> Bisecting the code commit 7076aada1040de4ed79a5977dbabdb5e5ea5e249 appears
>>>> to be the first one that have this issue.
>>>>
>>>> Signed-off-by: Frediano Ziglio <frediano.ziglio@...rix.com>
>>> In terms of the correctness of the fix,
>>>
>>> Reviewed-by: Andrew Cooper <andrew.cooper3@...rix.com>
> Should this also go in stable tree?

Very much so.  The change which exposed it for us was from 3.7 iirc, but
I believe it has been a latent bug for as long as the native early boot
code uses __USER_DS.

>>> However, I am not sure the comment is necessary.  The prevailing style
>>> is for no justification of loads of segment selectors on boot, and the
>>> comment itself refers simply to an interaction issue of 32bit on Xen
>>> when making use of sysenter.
>>>
>> Suggestion for the comment ??
>>
>> Frediano

My suggestion was to omit the comment entirely, or simplify it to just:

/* Xen starts us with XEN_FLAT_RING1_DS, but linux code expects __USER_DS */

Anyone who wants the full explanation can read the patch description.

~Andrew
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