Re: [PATCH] uio_pci_generic does not export memory resources

Alex Williamson
2012-06-10T17:38:44Z

On Sun, 2012-06-10 at 19:44 +0300, Michael S. Tsirkin wrote:
> On Sun, Jun 10, 2012 at 10:09:26AM -0600, Alex Williamson wrote:
> > On Sun, 2012-06-10 at 17:18 +0300, Michael S. Tsirkin wrote:
> > > On Fri, Jun 08, 2012 at 11:11:16AM -0600, Alex Williamson wrote:
> > > > On Fri, 2012-06-08 at 18:44 +0200, Hans J. Koch wrote:
> > > > > On Fri, Jun 08, 2012 at 06:16:18PM +0200, Andreas Hartmann wrote:
> > > > > > Hi Dominic,
> > > > > >
> > > > > > Dominic Eschweiler wrote:
> > > > > > > Am Freitag, den 08.06.2012, 08:16 -0600 schrieb Alex Williamson:
> > > > > > >> Yes, thanks Jan. This is exactly what VFIO does. VFIO provides
> > > > > > >> secure config space access, resource access, DMA mapping services, and
> > > > > > >> full interrupt support to userspace.
> > > > >
> > > > > VFIO is not a "better UIO". It *requires* an IOMMU. Dominic didn't say on
> > > > > what CPU he's working, so it's not clear if he can use VFIO at all.
> > > > >
> > > > > UIO is intended for general use with devices that have mappable registers
> > > > > and don't fit into any other subsystem. No more, no less.
> > > >
> > > > VFIO is a secure UIO.
> > >
> > > A secure UIO *for VFs*. I think that's why it's called VFIO :).
> > > Other stuff sometimes also works but no real guarantees, though
> > > VFIO tries to make sure you don't burn yourself too badly
> > > if it breaks.
> >
> > We do a little better than that. Multifunction devices that don't
> > explicitly report ACS support are grouped together, so we have security
> > for multifunction devices as well.
>
> How can you get security with insecure hardware?
>
> So you prevent the device from writing to host memory? Cool.
> Now guest puts a virus on an on-card flash, the
> moment device is assigned to another VM it will own that,
> or host if it's enabled in host.
>
> I can make up more silliness. Buggy userspace can brick the device,
> e.g. by damaging the internal eeprom memory, and these things were known
> to happen even by accident.
>
> Simply put if you want secure userspace drivers you must be able to
> trust your hardware for security and the only hardware that promises you
> security is a VF in an SRIOV device.

Next I suppose you're going to say assigning a NIC to a guest is
insecure because it could host a malicious OS that infects other systems
on the network. So to clarify, by secure, I mean that users of VFIO
devices don't have access to the host. The host still needs to be
suspicious of any data the user might have tainted after a device is
returned.

> > Either single of multifunction PFs
> > can have an option ROM, but since there's no defined mechanism to
> > program the ROM, we can't protect it. Secure boot actually helps us
> > here since the ROM loaded by the host BIOS or drivers would need to
> > verify the ROM before using it. Note that secure boot will likely close
> > off the pci-sysfs path uio_pci and KVM device assignment use to get
> > resources since it allows unprotected access to the system. VFIO
> > provides an interface where we control secure access, so should be
> > compatible with secure boot. Thanks,
> >
> > Alex
>
> IMHO all this means VFIO *works* not just for VFs.
> Not that it's secure.

By your argument above, not even VFs are "secure". A user could just as
easily taint a disk attached to an HBA VF...