vfio: Set DMA ownership for VFIO devices

Claim group dma ownership when an IOMMU group is set to a container,
and release the dma ownership once the iommu group is unset from the
container.

This change disallows some unsafe bridge drivers to bind to non-ACS
bridges while devices under them are assigned to user space. This is an
intentional enhancement and possibly breaks some existing
configurations. The recommendation to such an affected user would be
that the previously allowed host bridge driver was unsafe for this use
case and to continue to enable assignment of devices within that group,
the driver should be unbound from the bridge device or replaced with the
pci-stub driver.

For any bridge driver, we consider it unsafe if it satisfies any of the
following conditions:

  1) The bridge driver uses DMA. Calling pci_set_master() or calling any
     kernel DMA API (dma_map_*() and etc.) is an indicate that the
     driver is doing DMA.

  2) If the bridge driver uses MMIO, it should be tolerant to hostile
     userspace also touching the same MMIO registers via P2P DMA
     attacks.

If the bridge driver turns out to be a safe one, it could be used as
before by setting the driver's .driver_managed_dma field, just like what
we have done in the pcieport driver.
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/r/20220418005000.897664-8-baolu.lu@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/vfio/fsl-mc/vfio_fsl_mc.c

@@ -588,6 +588,7 @@ static struct fsl_mc_driver vfio_fsl_mc_driver = {
 		.name	= "vfio-fsl-mc",
 		.owner	= THIS_MODULE,
 	},
+	.driver_managed_dma = true,
 };
 
 static int __init vfio_fsl_mc_driver_init(void)

drivers/vfio/pci/vfio_pci.c

@@ -194,6 +194,7 @@ static struct pci_driver vfio_pci_driver = {
 	.remove			= vfio_pci_remove,
 	.sriov_configure	= vfio_pci_sriov_configure,
 	.err_handler		= &vfio_pci_core_err_handlers,
+	.driver_managed_dma	= true,
 };
 
 static void __init vfio_pci_fill_ids(void)

drivers/vfio/platform/vfio_amba.c

@@ -95,6 +95,7 @@ static struct amba_driver vfio_amba_driver = {
 		.name = "vfio-amba",
 		.owner = THIS_MODULE,
 	},
+	.driver_managed_dma = true,
 };
 
 module_amba_driver(vfio_amba_driver);

drivers/vfio/platform/vfio_platform.c

@@ -76,6 +76,7 @@ static struct platform_driver vfio_platform_driver = {
 	.driver	= {
 		.name	= "vfio-platform",
 	},
+	.driver_managed_dma = true,
 };
 
 module_platform_driver(vfio_platform_driver);

drivers/vfio/vfio.c

@@ -1198,6 +1198,8 @@ static void __vfio_group_unset_container(struct vfio_group *group)
 		driver->ops->detach_group(container->iommu_data,
 					  group->iommu_group);
 
+	iommu_group_release_dma_owner(group->iommu_group);
+
 	group->container = NULL;
 	wake_up(&group->container_q);
 	list_del(&group->container_next);
@@ -1282,13 +1284,19 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
 		goto unlock_out;
 	}
 
+	ret = iommu_group_claim_dma_owner(group->iommu_group, f.file);
+	if (ret)
+		goto unlock_out;
+
 	driver = container->iommu_driver;
 	if (driver) {
 		ret = driver->ops->attach_group(container->iommu_data,
 						group->iommu_group,
 						group->type);
-		if (ret)
+		if (ret) {
+			iommu_group_release_dma_owner(group->iommu_group);
 			goto unlock_out;
+		}
 	}
 
 	group->container = container;