[PATCH V2 09/12] virtio_ring: validate used buffer length

[Jason Wang <jasowang@redhat.com>]

This patch validate the used buffer length provided by the device
before trying to use it. This is done by record the in buffer length
in a new field in desc_state structure during virtqueue_add(), then we
can fail the virtqueue_get_buf() when we find the device is trying to
give us a used buffer length which is greater than the in buffer
length.

Since some drivers have already done the validation by itself, this
patch tries to makes the core validation optional. For the driver that
doesn't want the validation, it can set the validate_used to be
true (which could be overridden by force_used_validation). To be more
efficient, a dedicate array is used for storing the validate used
length, this helps to eliminate the cache stress if validation is done
by the driver.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/virtio/virtio_ring.c | 56 ++++++++++++++++++++++++++++++++++++
 include/linux/virtio.h       |  2 ++
 2 files changed, 58 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index d2ca0a7365f8..dee962bd8b04 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -14,6 +14,9 @@
 #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...)				\
@@ -182,6 +185,9 @@ struct vring_virtqueue {
 		} packed;
 	};
 
+	/* Per-descriptor in buffer length */
+	u32 *buflen;
+
 	/* How to notify other side. FIXME: commonalize hcalls! */
 	bool (*notify)(struct virtqueue *vq);
 
@@ -490,6 +496,7 @@ 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);
 
@@ -571,6 +578,7 @@ 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. */
@@ -610,6 +618,10 @@ 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);
@@ -784,6 +796,11 @@ 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;
@@ -1062,6 +1079,7 @@ 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);
@@ -1089,6 +1107,8 @@ 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;
 		}
 	}
 
@@ -1142,6 +1162,10 @@ 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);
@@ -1176,6 +1200,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 	unsigned int i, n, c, descs_used, err_idx;
 	__le16 head_flags, flags;
 	u16 head, id, prev, curr, avail_used_flags;
+	u32 buflen = 0;
 
 	START_USE(vq);
 
@@ -1250,6 +1275,8 @@ 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;
 		}
 	}
 
@@ -1269,6 +1296,10 @@ 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
@@ -1455,6 +1486,11 @@ 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;
@@ -1660,6 +1696,7 @@ 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;
 
@@ -1749,6 +1786,13 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	if (!vq->packed.desc_extra)
 		goto err_desc_extra;
 
+	if (!drv->validate_used || force_used_validation) {
+		vq->buflen = kmalloc_array(num, sizeof(*vq->buflen),
+					   GFP_KERNEL);
+		if (!vq->buflen)
+			goto err_buflen;
+	}
+
 	/* No callback?  Tell other side not to bother us. */
 	if (!callback) {
 		vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE;
@@ -1761,6 +1805,8 @@ 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:
@@ -2168,6 +2214,7 @@ 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))
@@ -2227,6 +2274,13 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	if (!vq->split.desc_extra)
 		goto err_extra;
 
+	if (!drv->validate_used || force_used_validation) {
+		vq->buflen = kmalloc_array(vring.num, sizeof(*vq->buflen),
+					   GFP_KERNEL);
+		if (!vq->buflen)
+			goto err_buflen;
+	}
+
 	/* Put everything in free lists. */
 	vq->free_head = 0;
 	memset(vq->split.desc_state, 0, vring.num *
@@ -2237,6 +2291,8 @@ 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:
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 0cd8685aeba4..79e4f6765e3a 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -153,6 +153,7 @@ size_t virtio_max_dma_size(struct virtio_device *vdev);
  * @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.
  * @validate: optional function to do early checks
+ * @validate_used: whether the driver can validate used buffer 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.
@@ -169,6 +170,7 @@ struct virtio_driver {
 	unsigned int feature_table_size;
 	const unsigned int *feature_table_legacy;
 	unsigned int feature_table_size_legacy;
+	bool validate_used;
 	int (*validate)(struct virtio_device *dev);
 	int (*probe)(struct virtio_device *dev);
 	void (*scan)(struct virtio_device *dev);
-- 
2.25.1