iommufd: Add check on user response code

The response code from user space is only allowed to be SUCCESS or
INVALID. All other values are treated by the device as a response code of
Response Failure according to PCI spec, section 10.4.2.1.  This response
disables the Page Request Interface for the Function.

Add a check in iommufd_fault_fops_write() to avoid invalid response
code.

Fixes: 07838f7 ("iommufd: Add iommufd fault object")
Link: https://lore.kernel.org/r/20240710083341.44617-3-baolu.lu@linux.intel.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: LuBaolu

drivers/iommu/iommufd/fault.c

@@ -305,6 +305,16 @@ static ssize_t iommufd_fault_fops_write(struct file *filep, const char __user *b
 		if (rc)
 			break;
 
+		static_assert((int)IOMMUFD_PAGE_RESP_SUCCESS ==
+			      (int)IOMMU_PAGE_RESP_SUCCESS);
+		static_assert((int)IOMMUFD_PAGE_RESP_INVALID ==
+			      (int)IOMMU_PAGE_RESP_INVALID);
+		if (response.code != IOMMUFD_PAGE_RESP_SUCCESS &&
+		    response.code != IOMMUFD_PAGE_RESP_INVALID) {
+			rc = -EINVAL;
+			break;
+		}
+
 		group = xa_erase(&fault->response, response.cookie);
 		if (!group) {
 			rc = -EINVAL;