linux-kernel - Re: [Xen-devel] [PATCH] xen: grant-table: Check truncation when giving access to a frame

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Date:	Mon, 13 Jun 2016 12:10:03 +0100
From:	Julien Grall <julien.grall@....com>
To:	David Vrabel <david.vrabel@...rix.com>, boris.ostrovsky@...cle.com,
	jgross@...e.com, sstabellini@...nel.org, konrad.wilk@...cle.com
Cc:	andrew.cooper3@...rix.com, xen-devel@...ts.xen.org,
	linux-kernel@...r.kernel.org, JBeulich@...e.com,
	steve.capper@....com
Subject: Re: [Xen-devel] [PATCH] xen: grant-table: Check truncation when
 giving access to a frame

Hi David,

On 13/06/16 11:57, David Vrabel wrote:
> On 13/06/16 11:50, Julien Grall wrote:
>> The version 1 of the grant-table protocol only supports frame encoded on
>> 32-bit.
>>
>> When the platform is supporting 48-bit physical address, the frame will
>> be encoded on 36-bit which will lead a truncation and give access to
>> the wrong frame.
>>
>> On ARM Xen will always allow the guest to use all the physical address,
>> although today the RAM is always located under 40-bits (see
>> xen/include/public/arch-arm.h).
>>
>> Add a truncation check in gnttab_update_entry_v1 to prevent the guest to
>> give access to the wrong frame.
>
> In hindsight, we shouldn't have dropped the V2 support from Linux.
> Should we reinstate it?

What were the reasons to drop the v2 support from Linux? More 
importantly why people did choose to stay on v1?

Cheers,

-- 
Julien Grall