Re: [Xen-devel] granting access to MSI-X table and pending bit array

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Jul 07, 2010 at 11:14:04AM +0100, Jan Beulich wrote:
> The original implementation (c/s 17536) disallowed access to these
> after granting access to all BAR specified resources (i.e. this was
> almost correct, except for a small time window during which the
> memory was accessible to the guest and except for hiding the
> pending bit array from the guest), but this got reverted with c/s
> 20171.
> 
> Afaics this is a security problem, as CPU accesses to the granted
> memory don't go through any IOMMU and hence there's no place
> these could be filtered out even in a supposedly secure environment
> (not that I think devices accesses would be filtered at present, but
> for those this would at least be possible ), and such accesses could
> inadvertently or maliciously unmask masked vectors or modify the
> message address/data fields.
> 
> Imo the pending bit array must be granted read-only access to the
> guest (instead of either granting full access or no access at all),
> with the potential side effect of also granting read-only access to
> the table. And I would even think that this shouldn't be done in the
> tools, but rather in Xen itself (since it knows of all the PCI devices
> and their respective eventual MSI-X address ranges), thus at once
> eliminating any timing windows.

That sounds sensible. You got a patch ready?
> 
> Jan

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