Re: [PATCH V2] device-assignment pci: correct pci config size default for cap version 2 endpoints

[Alex Williamson <alex.williamson@redhat.com>]

On Sun, 2011-07-24 at 11:36 +0300, Michael S. Tsirkin wrote:
> On Thu, Jul 21, 2011 at 11:02:53AM -0600, Alex Williamson wrote:
> > This is crazy, why would we only test this for PCI_CAP_ID_EXP?  If the
> > test is going to go in device-assignment, we need to wrap
> > pci_add_capability and do it for all callers.  However, maybe we can get
> > MST to take it in pci_add_capability() if we make the test more
> > complete...  something like:
> > 
> > if ((pos < 256 && size > 256 - pos) ||
> >     (pci_config_size() > 256 && pos > 256 &&
> >      size > pci_config_size() - pos)) {
> >    ... badness
> > 
> > Thanks,
> > 
> > Alex
> 
> We expect device assignment to be able to corrupt
> guest memory but not qemu memory. So we must validate

Gee, thanks.

> whatever we get from the device, and I think this
> validation belongs in device-assignment.c:
> 
> IOW I think input should be validated where it's
> input, while we still know it's untrusted,
> instead of relying on core to validate parameters.
> 
> Makes sense?

No, not really.  Why should the core "trust" anything?  This is a basic,
simply sanity test, why push it out to the leaf driver when pushing it
into the core provides the sanity test for everyone?  Is it beneath an
emulated driver to pass such a test?  Thanks,

Alex