Re: [PATCH] xen: add gntdev

[Roger Pau Monné <roger.pau%citrix.com@localhost>]

On 05/12/12 11:15, Manuel Bouyer wrote:
> On Tue, Dec 04, 2012 at 03:07:39PM -0500, Thor Lancelot Simon wrote:
>> On Tue, Dec 04, 2012 at 04:26:19PM +0100, Roger Pau Monn? wrote:
>>>
>>> Independently of what we end up doing as default for handling raw file
>>> disks, could someone review this code?
>>>
>>> It's the first time I've done a device, so someone with more experience
>>> should review it.
>>
>> I am not sure I entirely follow what this code's doing, but it seems to
>> me it may allow arbitrary physical pages to be exposed to userspace
>> processes in dom0 -- or in a domU, albeit only if dom0 userspace says so.
>>
>> Is that a correct understanding of one of its effects?  If so, there's
>> a problem, since not being able to do precisely that is one important
>> assumption of the 4.4BSD security model.
> 
> If I read it properly, It allows only to map pages that are part of a
> grant. You provide the ioctl a grant reference, and this is what
> the driver uses to find the physical pages. So it should be limited to
> pages that are referenced by a grant.

Yes, it should be limited to grant pages, you are not able to map
arbitrary mfns.