vfio: Have the core code decode the VFIO_DEVICE_FEATURE ioctl

Invoke a new device op 'device_feature' to handle just the data array
portion of the command. This lifts the ioctl validation to the core code
and makes it simpler for either the core code, or layered drivers, to
implement their own feature values.

Provide vfio_check_feature() to consolidate checking the flags/etc against
what the driver supports.

Link: https://lore.kernel.org/all/20220224142024.147653-9-yishaih@nvidia.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 76191d7abed1..550c28f2ef60 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -55,6 +55,7 @@ struct vfio_device {
  * @match: Optional device name match callback (return: 0 for no-match, >0 for
  *         match, -errno for abort (ex. match with insufficient or incorrect
  *         additional args)
+ * @device_feature: Optional, fill in the VFIO_DEVICE_FEATURE ioctl
  */
 struct vfio_device_ops {
 	char	*name;
@@ -69,8 +70,39 @@ struct vfio_device_ops {
 	int	(*mmap)(struct vfio_device *vdev, struct vm_area_struct *vma);
 	void	(*request)(struct vfio_device *vdev, unsigned int count);
 	int	(*match)(struct vfio_device *vdev, char *buf);
+	int	(*device_feature)(struct vfio_device *device, u32 flags,
+				  void __user *arg, size_t argsz);
 };
 
+/**
+ * vfio_check_feature - Validate user input for the VFIO_DEVICE_FEATURE ioctl
+ * @flags: Arg from the device_feature op
+ * @argsz: Arg from the device_feature op
+ * @supported_ops: Combination of VFIO_DEVICE_FEATURE_GET and SET the driver
+ *                 supports
+ * @minsz: Minimum data size the driver accepts
+ *
+ * For use in a driver's device_feature op. Checks that the inputs to the
+ * VFIO_DEVICE_FEATURE ioctl are correct for the driver's feature. Returns 1 if
+ * the driver should execute the get or set, otherwise the relevant
+ * value should be returned.
+ */
+static inline int vfio_check_feature(u32 flags, size_t argsz, u32 supported_ops,
+				    size_t minsz)
+{
+	if ((flags & (VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_SET)) &
+	    ~supported_ops)
+		return -EINVAL;
+	if (flags & VFIO_DEVICE_FEATURE_PROBE)
+		return 0;
+	/* Without PROBE one of GET or SET must be requested */
+	if (!(flags & (VFIO_DEVICE_FEATURE_GET | VFIO_DEVICE_FEATURE_SET)))
+		return -EINVAL;
+	if (argsz < minsz)
+		return -EINVAL;
+	return 1;
+}
+
 void vfio_init_group_dev(struct vfio_device *device, struct device *dev,
 			 const struct vfio_device_ops *ops);
 void vfio_uninit_group_dev(struct vfio_device *device);