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

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Message-ID: <5252815E.70504@citrix.com>
Date:	Mon, 7 Oct 2013 10:39:42 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Andrew Cooper <andrew.cooper3@...rix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Frediano Ziglio <frediano.ziglio@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.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 14:33, Andrew Cooper wrote:
> 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:

Suggesting comments should be omitted because other code is poorly
commented seems odd to me.

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

I do think this comment better summarizes the reason for loading the
segment registers so I'd prefer this.

David
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