Re: [PATCH 1/1] direct mmio for passthrough - kernel part

Anthony Liguori
2008-04-01T18:23:42Z

Andrea Arcangeli wrote:
> On Tue, Apr 01, 2008 at 06:18:07PM +0100, Daniel P. Berrange wrote:
>
>> and very few application domains are allowed to access them. THe KVM/QEMU
>> policy will not allow this for example. Basically on the X server, HAL and
>> dmidecode have access in current policy. It would be undesirable to have to
>> all KVM guests full access to /dev/mem, so a more fine grained access method
>> would have benefits here.
>>
>
> But pci-passthrough can give a root on the host even to the ring0
> guest, just like /dev/mem without VT-d, so there's no muchx difference
> with using /dev/mem as far as security is concerned. Only on the CPUs
> including VT-d it's possible to retain a mostly equivalent security
> level despite pci-passthrough.
>

Eventually, most machines with have an IOMMU so that's the assumption to
design to. It is true that PCI pass-through w/o VT-d is always going to
be equivalent to /dev/mem access but it's really a special case. Unless
you have an IOMMU, you would not do PCI pass-through if you cared at all
about security/reliability.

Regards,

Anthony Liguori