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.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/vfio/pci/vfio_pci.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

On Thu, Jul 12, 2018 at 04:33:04PM -0600, Alex Williamson wrote:
> 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.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  drivers/vfio/pci/vfio_pci.c |   13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index b423a309a6e0..f372f209c5c2 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -1189,6 +1189,19 @@ 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;
>

On Thu, Jul 12, 2018 at 04:33:04PM -0600, Alex Williamson wrote:
> 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.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>