vDPA/ifcvf: get_config_size should return a value no greater than dev implementation

Drivers must not access a BAR outside the capability length,
and for a virtio device, ifcvf driver should not report any non-standard
capability contents to the upper layers.

Function ifcvf_get_config_size() is introduced here to return a safe value
of the device config capability size.
Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Message-Id: <20220722115309.82746-2-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/ifcvf/ifcvf_base.c

@@ -127,6 +127,7 @@ int ifcvf_init_hw(struct ifcvf_hw *hw, struct pci_dev *pdev)
 			break;
 		case VIRTIO_PCI_CAP_DEVICE_CFG:
 			hw->dev_cfg = get_cap_addr(hw, &cap);
+			hw->cap_dev_config_size = le32_to_cpu(cap.length);
 			IFCVF_DBG(pdev, "hw->dev_cfg = %p\n", hw->dev_cfg);
 			break;
 		}
@@ -232,15 +233,23 @@ int ifcvf_verify_min_features(struct ifcvf_hw *hw, u64 features)
 u32 ifcvf_get_config_size(struct ifcvf_hw *hw)
 {
 	struct ifcvf_adapter *adapter;
+	u32 net_config_size = sizeof(struct virtio_net_config);
+	u32 blk_config_size = sizeof(struct virtio_blk_config);
+	u32 cap_size = hw->cap_dev_config_size;
 	u32 config_size;
 
 	adapter = vf_to_adapter(hw);
+	/* If the onboard device config space size is greater than
+	 * the size of struct virtio_net/blk_config, only the spec
+	 * implementing contents size is returned, this is very
+	 * unlikely, defensive programming.
+	 */
 	switch (hw->dev_type) {
 	case VIRTIO_ID_NET:
-		config_size = sizeof(struct virtio_net_config);
+		config_size = min(cap_size, net_config_size);
 		break;
 	case VIRTIO_ID_BLOCK:
-		config_size = sizeof(struct virtio_blk_config);
+		config_size = min(cap_size, blk_config_size);
 		break;
 	default:
 		config_size = 0;

drivers/vdpa/ifcvf/ifcvf_base.h

@@ -87,6 +87,8 @@ struct ifcvf_hw {
 	int config_irq;
 	int vqs_reused_irq;
 	u16 nr_vring;
+	/* VIRTIO_PCI_CAP_DEVICE_CFG size */
+	u32 cap_dev_config_size;
 };
 
 struct ifcvf_adapter {