vfio-pci: Disable binding to PFs with SR-IOV enabled

We expect to receive PFs with SR-IOV disabled, however some host
drivers leave SR-IOV enabled at unbind.  This puts us in a state where
we can potentially assign both the PF and the VF, leading to both
functionality as well as security concerns due to lack of managing the
SR-IOV state as well as vendor dependent isolation from the PF to VF.
If we were to attempt to actively disable SR-IOV on driver probe, we
risk VF bound drivers blocking, potentially risking live lock
scenarios.  Therefore simply refuse to bind to PFs with SR-IOV enabled
with a warning message indicating the issue.  Users can resolve this
by re-binding to the host driver and disabling SR-IOV before
attempting to use the device with vfio-pci.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 7fe2748ba101..9979d3ba9e52 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -1193,6 +1193,19 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
         if (pdev->hdr_type != PCI_HEADER_TYPE_NORMAL)
                 return -EINVAL;
 
+        /*
+         * Prevent binding to PFs with VFs enabled, this too easily allows
+         * userspace instance with VFs and PFs from the same device, which
+         * cannot work.  Disabling SR-IOV here would initiate removing the
+         * VFs, which would unbind the driver, which is prone to blocking
+         * if that VF is also in use by vfio-pci.  Just reject these PFs
+         * and let the user sort it out.
+         */
+        if (pci_num_vf(pdev)) {
+                pci_warn(pdev, "Cannot bind to PF with SR-IOV enabled\n");
+                return -EBUSY;
+        }
+
         group = vfio_iommu_group_get(&pdev->dev);
         if (!group)
                 return -EINVAL;