xen/pci: Allocate memory for physdev_pci_device_add's optarr

physdev_pci_device_add's optarr[] is a zero-sized array and therefore
reference to add.optarr[0] is accessing memory that does not belong to
the 'add' variable.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

drivers/xen/pci.c

@@ -41,24 +41,29 @@ static int xen_add_device(struct device *dev)
 #endif
 
 	if (pci_seg_supported) {
-		struct physdev_pci_device_add add = {
-			.seg = pci_domain_nr(pci_dev->bus),
-			.bus = pci_dev->bus->number,
-			.devfn = pci_dev->devfn
+		struct {
+			struct physdev_pci_device_add add;
+			uint32_t pxm;
+		} add_ext = {
+			.add.seg = pci_domain_nr(pci_dev->bus),
+			.add.bus = pci_dev->bus->number,
+			.add.devfn = pci_dev->devfn
 		};
+		struct physdev_pci_device_add *add = &add_ext.add;
+
 #ifdef CONFIG_ACPI
 		acpi_handle handle;
 #endif
 
 #ifdef CONFIG_PCI_IOV
 		if (pci_dev->is_virtfn) {
-			add.flags = XEN_PCI_DEV_VIRTFN;
-			add.physfn.bus = physfn->bus->number;
-			add.physfn.devfn = physfn->devfn;
+			add->flags = XEN_PCI_DEV_VIRTFN;
+			add->physfn.bus = physfn->bus->number;
+			add->physfn.devfn = physfn->devfn;
 		} else
 #endif
 		if (pci_ari_enabled(pci_dev->bus) && PCI_SLOT(pci_dev->devfn))
-			add.flags = XEN_PCI_DEV_EXTFN;
+			add->flags = XEN_PCI_DEV_EXTFN;
 
 #ifdef CONFIG_ACPI
 		handle = ACPI_HANDLE(&pci_dev->dev);
@@ -77,16 +82,16 @@ static int xen_add_device(struct device *dev)
 				status = acpi_evaluate_integer(handle, "_PXM",
 							       NULL, &pxm);
 				if (ACPI_SUCCESS(status)) {
-					add.optarr[0] = pxm;
-					add.flags |= XEN_PCI_DEV_PXM;
+					add->optarr[0] = pxm;
+					add->flags |= XEN_PCI_DEV_PXM;
 					break;
 				}
 				status = acpi_get_parent(handle, &handle);
 			} while (ACPI_SUCCESS(status));
 		}
 #endif /* CONFIG_ACPI */
 
-		r = HYPERVISOR_physdev_op(PHYSDEVOP_pci_device_add, &add);
+		r = HYPERVISOR_physdev_op(PHYSDEVOP_pci_device_add, add);
 		if (r != -ENOSYS)
 			return r;
 		pci_seg_supported = false;