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 12:12:49 +0000
From:	Paul Durrant <Paul.Durrant@...rix.com>
To:	Julien Grall <julien.grall@....com>,
	"boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	"jgross@...e.com" <jgross@...e.com>,
	"sstabellini@...nel.org" <sstabellini@...nel.org>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>
CC:	"steve.capper@....com" <steve.capper@....com>,
	Andrew Cooper <Andrew.Cooper3@...rix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"JBeulich@...e.com" <JBeulich@...e.com>
Subject: RE: [Xen-devel] [PATCH] xen: grant-table: Check truncation when
 giving	access to a frame

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@...ts.xen.org] On Behalf Of
> Julien Grall
> Sent: 13 June 2016 11:51
> To: boris.ostrovsky@...cle.com; David Vrabel; jgross@...e.com;
> sstabellini@...nel.org; konrad.wilk@...cle.com
> Cc: steve.capper@....com; Andrew Cooper; linux-kernel@...r.kernel.org;
> xen-devel@...ts.xen.org; Julien Grall; JBeulich@...e.com
> Subject: [Xen-devel] [PATCH] xen: grant-table: Check truncation when giving
> access to a frame
> 
> 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.
> 
> Signed-off-by: Julien Grall <julien.grall@....com>
> 
> ---
>     This is limiting us to a 44-bit address space whilst ARM can support
>     up to 48-bit today. This number of bit will increase to 52-bit in
>     upcoming processors [1].
> 
>     It might be good to start thinking to extend the version 1 of the
>     protocol to use 64-bit frame number.

...or simply use version 2 of the protocol.

  Paul