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

[Paul Durrant]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of
> Julien Grall
> Sent: 13 June 2016 11:51
> To: boris.ostrovsky@xxxxxxxxxx; David Vrabel; jgross@xxxxxxxx;
> sstabellini@xxxxxxxxxx; konrad.wilk@xxxxxxxxxx
> Cc: steve.capper@xxxxxxx; Andrew Cooper; linux-kernel@xxxxxxxxxxxxxxx;
> xen-devel@xxxxxxxxxxxxx; Julien Grall; JBeulich@xxxxxxxx
> 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@xxxxxxx>
> 
> ---
>     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