Re: [Xen-devel] readonly grants

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2011-10-26 at 17:46 +0100, Mohammad Hedayati wrote:
> After mapping a readonly granted page in a PV guest, the guest can try
> to change his l1 page table entry, faulting into Xen. Here xen
> emulates the update operation, but first it must check whether the
> modification is allowed or not (i.e. the grant is readonly or not).
> I'm looking through the code, but I can't find where this checking is
> done. Can anyone help?!

I don't think a guest can modify any grant mapping that way, read only
or otherwise, they have to use the GNTTABOP hypercalls.

The thing which prevents it is that the page is really owned by another
domain so the get_page_from_l1e in ptwr_emulated_update will fail.

(disclaimer, I'm not really sure about this...)

Ian.


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