On Wed, 11 Mar 2020 15:58:52 -0600 Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > 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, even if by simply resetting itself. The degree to which a PF > can access the data passed through a VF or interfere with its operation > is dependent on a given SR-IOV implementation. Therefore we want to > avoid a scenario where an existing vfio-pci based userspace driver might > assume the PF driver is trusted, for example assigning a PF to one VM > and VF to another with some expectation of isolation. IOMMU grouping > could be a solution to this, but imposes an unnecessarily strong > relationship between PF and VF drivers if they need to operate with the > same IOMMU context. Instead we introduce a "VF token", which is > essentially just a shared secret between PF and VF drivers, implemented > as a UUID. > > The VF token can be set by a vfio-pci based PF driver and must be known > by the vfio-pci based VF driver in order to gain access to the device. > This allows the degree to which this VF token is considered secret to be > determined by the applications and environment. For example a VM might > generate a random UUID known only internally to the hypervisor while a > userspace networking appliance might use a shared, or even well know, > UUID among the application drivers. > > To incorporate this VF token, the VFIO_GROUP_GET_DEVICE_FD interface is > extended to accept key=value pairs in addition to the device name. This > allows us to most easily deny user access to the device without risk > that existing userspace drivers assume region offsets, IRQs, and other > device features, leading to more elaborate error paths. The format of > these options are expected to take the form: > > "$DEVICE_NAME $OPTION1=$VALUE1 $OPTION2=$VALUE2" > > Where the device name is always provided first for compatibility and > additional options are specified in a space separated list. The > relation between and requirements for the additional options will be > vfio bus driver dependent, however unknown or unused option within this > schema should return error. This allow for future use of unknown > options as well as a positive indication to the user that an option is > used. > > An example VF token option would take this form: > > "0000:03:00.0 vf_token=2ab74924-c335-45f4-9b16-8569e5b08258" > > When accessing a VF where the PF is making use of vfio-pci, the user > MUST provide the current vf_token. When accessing a PF, the user MUST > provide the current vf_token IF there are active VF users or MAY provide > a vf_token in order to set the current VF token when no VF users are > active. The former requirement assures VF users that an unassociated > driver cannot usurp the PF device. These semantics also imply that a > VF token MUST be set by a PF driver before VF drivers can access their > device, the default token is random and mechanisms to read the token are > not provided in order to protect the VF token of previous users. Use of > the vf_token option outside of these cases will return an error, as > discussed above. > > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > --- > drivers/vfio/pci/vfio_pci.c | 198 +++++++++++++++++++++++++++++++++++ > drivers/vfio/pci/vfio_pci_private.h | 8 + > 2 files changed, 205 insertions(+), 1 deletion(-) Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
