> From: Alex Williamson <alex.williamson@xxxxxxxxxx> > Sent: Wednesday, February 5, 2020 7:06 AM > To: kvm@xxxxxxxxxxxxxxx > Subject: [RFC PATCH 3/7] vfio/pci: Introduce VF token > > If we enable SR-IOV on a vfio-pci owned PF, the resulting VFs are not > fully isolated from the PF. The PF can always cause a denial of > service to the VF, if not access data passed through the VF directly. > This is why vfio-pci currently does not bind to PFs with SR-IOV enabled > and does not provide access itself to enabling SR-IOV on a PF. The > IOMMU grouping mechanism might allow us a solution to this lack of > isolation, however the deficiency isn't actually in the DMA path, so > much as the potential cooperation between PF and VF devices. Also, > if we were to force VFs into the same IOMMU group as the PF, we severely > limit the utility of having independent drivers managing PFs and VFs > with vfio. > > Therefore we introduce the concept of a VF token. The token is > implemented as a UUID and represents a shared secret which must be set > by the PF driver and used by the VF drivers in order to access a vfio > device file descriptor for the VF. The ioctl to set the VF token will > be provided in a later commit, this commit implements the underlying > infrastructure. The concept here is to augment the string the user > passes to match a device within a group in order to retrieve access to > the device descriptor. For example, rather than passing only the PCI > device name (ex. "0000:03:00.0") the user would also pass a vf_token > UUID (ex. "2ab74924-c335-45f4-9b16-8569e5b08258"). The device match > string therefore becomes: > > "0000:03:00.0 vf_token=2ab74924-c335-45f4-9b16-8569e5b08258" > > This syntax is expected to be extensible to future options as well, with > the standard being: > > "$DEVICE_NAME $OPTION1=$VALUE1 $OPTION2=$VALUE2" > > The device name must be first and option=value pairs are separated by > spaces. > > The vf_token option is only required for VFs where the PF device is > bound to vfio-pci. There is no change for PFs using existing host > drivers. > > Note that in order to protect existing VF users, not only is it required > to set a vf_token on the PF before VFs devices can be accessed, but also > if there are existing VF users, (re)opening the PF device must also > provide the current vf_token as authentication. This is intended to > prevent a VF driver starting with a trusted PF driver and later being > replaced by an unknown driver. A vf_token is not required to open the > PF device when none of the VF devices are in use by vfio-pci drivers. So vfio_token is a kind of per-PF token? Regards, Yi Liu
