Revert "virtio_ring: validate used buffer length"

This reverts commit 939779f.

Attempts to validate length in the core did not work out: there turn out
to exist multiple broken devices, and in particular legacy devices are
known to be broken in this respect.

We have ideas for handling this better in the next version but for now
let's revert to a known good state to make sure drivers work for people.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Author: mstsirkin

drivers/virtio/virtio_ring.c

@@ -14,9 +14,6 @@
 #include <linux/spinlock.h>
 #include <xen/xen.h>
 
-static bool force_used_validation = false;
-module_param(force_used_validation, bool, 0444);
-
 #ifdef DEBUG
 /* For development, we want to crash whenever the ring is screwed. */
 #define BAD_RING(_vq, fmt, args...)				\
@@ -185,9 +182,6 @@ struct vring_virtqueue {
 		} packed;
 	};
 
-	/* Per-descriptor in buffer length */
-	u32 *buflen;
-
 	/* How to notify other side. FIXME: commonalize hcalls! */
 	bool (*notify)(struct virtqueue *vq);
 
@@ -496,7 +490,6 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	unsigned int i, n, avail, descs_used, prev, err_idx;
 	int head;
 	bool indirect;
-	u32 buflen = 0;
 
 	START_USE(vq);
 
@@ -578,7 +571,6 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 						     VRING_DESC_F_NEXT |
 						     VRING_DESC_F_WRITE,
 						     indirect);
-			buflen += sg->length;
 		}
 	}
 	/* Last one doesn't continue. */
@@ -618,10 +610,6 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	else
 		vq->split.desc_state[head].indir_desc = ctx;
 
-	/* Store in buffer length if necessary */
-	if (vq->buflen)
-		vq->buflen[head] = buflen;
-
 	/* Put entry in available array (but don't update avail->idx until they
 	 * do sync). */
 	avail = vq->split.avail_idx_shadow & (vq->split.vring.num - 1);
@@ -796,11 +784,6 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq,
 		BAD_RING(vq, "id %u is not a head!\n", i);
 		return NULL;
 	}
-	if (vq->buflen && unlikely(*len > vq->buflen[i])) {
-		BAD_RING(vq, "used len %d is larger than in buflen %u\n",
-			*len, vq->buflen[i]);
-		return NULL;
-	}
 
 	/* detach_buf_split clears data, so grab it now. */
 	ret = vq->split.desc_state[i].data;
@@ -1079,7 +1062,6 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 	unsigned int i, n, err_idx;
 	u16 head, id;
 	dma_addr_t addr;
-	u32 buflen = 0;
 
 	head = vq->packed.next_avail_idx;
 	desc = alloc_indirect_packed(total_sg, gfp);
@@ -1109,8 +1091,6 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 			desc[i].addr = cpu_to_le64(addr);
 			desc[i].len = cpu_to_le32(sg->length);
 			i++;
-			if (n >= out_sgs)
-				buflen += sg->length;
 		}
 	}
 
@@ -1164,10 +1144,6 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 	vq->packed.desc_state[id].indir_desc = desc;
 	vq->packed.desc_state[id].last = id;
 
-	/* Store in buffer length if necessary */
-	if (vq->buflen)
-		vq->buflen[id] = buflen;
-
 	vq->num_added += 1;
 
 	pr_debug("Added buffer head %i to %p\n", head, vq);
@@ -1203,7 +1179,6 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 	__le16 head_flags, flags;
 	u16 head, id, prev, curr, avail_used_flags;
 	int err;
-	u32 buflen = 0;
 
 	START_USE(vq);
 
@@ -1283,8 +1258,6 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 					1 << VRING_PACKED_DESC_F_AVAIL |
 					1 << VRING_PACKED_DESC_F_USED;
 			}
-			if (n >= out_sgs)
-				buflen += sg->length;
 		}
 	}
 
@@ -1304,10 +1277,6 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 	vq->packed.desc_state[id].indir_desc = ctx;
 	vq->packed.desc_state[id].last = prev;
 
-	/* Store in buffer length if necessary */
-	if (vq->buflen)
-		vq->buflen[id] = buflen;
-
 	/*
 	 * A driver MUST NOT make the first descriptor in the list
 	 * available before all subsequent descriptors comprising
@@ -1494,11 +1463,6 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
 		BAD_RING(vq, "id %u is not a head!\n", id);
 		return NULL;
 	}
-	if (vq->buflen && unlikely(*len > vq->buflen[id])) {
-		BAD_RING(vq, "used len %d is larger than in buflen %u\n",
-			*len, vq->buflen[id]);
-		return NULL;
-	}
 
 	/* detach_buf_packed clears data, so grab it now. */
 	ret = vq->packed.desc_state[id].data;
@@ -1704,7 +1668,6 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	struct vring_virtqueue *vq;
 	struct vring_packed_desc *ring;
 	struct vring_packed_desc_event *driver, *device;
-	struct virtio_driver *drv = drv_to_virtio(vdev->dev.driver);
 	dma_addr_t ring_dma_addr, driver_event_dma_addr, device_event_dma_addr;
 	size_t ring_size_in_bytes, event_size_in_bytes;
 
@@ -1794,15 +1757,6 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	if (!vq->packed.desc_extra)
 		goto err_desc_extra;
 
-	if (!drv->suppress_used_validation || force_used_validation) {
-		vq->buflen = kmalloc_array(num, sizeof(*vq->buflen),
-					   GFP_KERNEL);
-		if (!vq->buflen)
-			goto err_buflen;
-	} else {
-		vq->buflen = NULL;
-	}
-
 	/* No callback?  Tell other side not to bother us. */
 	if (!callback) {
 		vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE;
@@ -1815,8 +1769,6 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	spin_unlock(&vdev->vqs_list_lock);
 	return &vq->vq;
 
-err_buflen:
-	kfree(vq->packed.desc_extra);
 err_desc_extra:
 	kfree(vq->packed.desc_state);
 err_desc_state:
@@ -2224,7 +2176,6 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 					void (*callback)(struct virtqueue *),
 					const char *name)
 {
-	struct virtio_driver *drv = drv_to_virtio(vdev->dev.driver);
 	struct vring_virtqueue *vq;
 
 	if (virtio_has_feature(vdev, VIRTIO_F_RING_PACKED))
@@ -2284,15 +2235,6 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	if (!vq->split.desc_extra)
 		goto err_extra;
 
-	if (!drv->suppress_used_validation || force_used_validation) {
-		vq->buflen = kmalloc_array(vring.num, sizeof(*vq->buflen),
-					   GFP_KERNEL);
-		if (!vq->buflen)
-			goto err_buflen;
-	} else {
-		vq->buflen = NULL;
-	}
-
 	/* Put everything in free lists. */
 	vq->free_head = 0;
 	memset(vq->split.desc_state, 0, vring.num *
@@ -2303,8 +2245,6 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	spin_unlock(&vdev->vqs_list_lock);
 	return &vq->vq;
 
-err_buflen:
-	kfree(vq->split.desc_extra);
 err_extra:
 	kfree(vq->split.desc_state);
 err_state:

include/linux/virtio.h

@@ -152,7 +152,6 @@ size_t virtio_max_dma_size(struct virtio_device *vdev);
  * @feature_table_size: number of entries in the feature table array.
  * @feature_table_legacy: same as feature_table but when working in legacy mode.
  * @feature_table_size_legacy: number of entries in feature table legacy array.
- * @suppress_used_validation: set to not have core validate used length
  * @probe: the function to call when a device is found.  Returns 0 or -errno.
  * @scan: optional function to call after successful probe; intended
  *    for virtio-scsi to invoke a scan.
@@ -169,7 +168,6 @@ struct virtio_driver {
 	unsigned int feature_table_size;
 	const unsigned int *feature_table_legacy;
 	unsigned int feature_table_size_legacy;
-	bool suppress_used_validation;
 	int (*validate)(struct virtio_device *dev);
 	int (*probe)(struct virtio_device *dev);
 	void (*scan)(struct virtio_device *dev);