Jason Wang
2022-Jun-14 07:45 UTC
[PATCH] virtio_ring : keep used_wrap_counter in vq->last_used_idx
On Tue, Jun 14, 2022 at 1:38 PM Albert Huang <huangjie.albert at bytedance.com> wrote:> > From: "huangjie.albert" <huangjie.albert at bytedance.com> > > the used_wrap_counter and the vq->last_used_idx may get > out of sync if they are separate assignment?and interrupt > might use an incorrect value to check for the used index. > > for example:OOB access > ksoftirqd may consume the packet and it will call: > virtnet_poll > -->virtnet_receive > -->virtqueue_get_buf_ctx > -->virtqueue_get_buf_ctx_packed > and in virtqueue_get_buf_ctx_packed: > > vq->last_used_idx += vq->packed.desc_state[id].num; > if (unlikely(vq->last_used_idx >= vq->packed.vring.num)) { > vq->last_used_idx -= vq->packed.vring.num; > vq->packed.used_wrap_counter ^= 1; > } > > if at the same time, there comes a vring interrupt?in vring_interrupt: > we will call: > vring_interrupt > -->more_used > -->more_used_packed > -->is_used_desc_packed > in is_used_desc_packed, the last_used_idx maybe >= vq->packed.vring.num. > so this could case a memory out of bounds bug. > > this patch is to keep the used_wrap_counter in vq->last_used_idx > so we can get the correct value to check for used index in interrupt. > > Signed-off-by: huangjie.albert <huangjie.albert at bytedance.com> > --- > drivers/virtio/virtio_ring.c | 60 ++++++++++++++++++-------------- > include/uapi/linux/virtio_ring.h | 6 ++++ > 2 files changed, 40 insertions(+), 26 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 13a7348cedff..35c3750e89e1 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -111,7 +111,12 @@ struct vring_virtqueue { > /* Number we've added since last sync. */ > unsigned int num_added; > > - /* Last used index we've seen. */ > + /* Last used index we've seen. > + * for split ring, it just contains last used index > + * for packed ring, it not only contains last used index, but also > + * used_wrap_counter, the VRING_PACKED_USED_INDEX_F_WRAP_CTR is > + * the bit shift in last_used_idx > + */ > u16 last_used_idx; > > /* Hint for event idx: already triggered no need to disable. */ > @@ -154,9 +159,6 @@ struct vring_virtqueue { > /* Driver ring wrap counter. */ > bool avail_wrap_counter; > > - /* Device ring wrap counter. */ > - bool used_wrap_counter; > - > /* Avail used flags. */ > u16 avail_used_flags; > > @@ -1397,6 +1399,9 @@ static inline bool is_used_desc_packed(const struct vring_virtqueue *vq, > bool avail, used; > u16 flags; > > + if (idx >= vq->packed.vring.num) > + return false;I wonder if we can avoid this trick, more below.> + > flags = le16_to_cpu(vq->packed.vring.desc[idx].flags); > avail = !!(flags & (1 << VRING_PACKED_DESC_F_AVAIL)); > used = !!(flags & (1 << VRING_PACKED_DESC_F_USED)); > @@ -1406,8 +1411,12 @@ static inline bool is_used_desc_packed(const struct vring_virtqueue *vq, > > static inline bool more_used_packed(const struct vring_virtqueue *vq) > { > - return is_used_desc_packed(vq, vq->last_used_idx, > - vq->packed.used_wrap_counter); > + u16 last_used; > + bool used_wrap_counter; > + > + last_used = vq->last_used_idx & ~(1 << VRING_PACKED_USED_INDEX_F_WRAP_CTR); > + used_wrap_counter = !!((vq->last_used_idx) >> VRING_PACKED_USED_INDEX_F_WRAP_CTR); > + return is_used_desc_packed(vq, last_used, used_wrap_counter); > } > > static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > @@ -1416,6 +1425,7 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > { > struct vring_virtqueue *vq = to_vvq(_vq); > u16 last_used, id; > + bool used_wrap_counter; > void *ret; > > START_USE(vq); > @@ -1434,7 +1444,8 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > /* Only get used elements after they have been exposed by host. */ > virtio_rmb(vq->weak_barriers); > > - last_used = vq->last_used_idx; > + used_wrap_counter = !!((vq->last_used_idx >> VRING_PACKED_USED_INDEX_F_WRAP_CTR)); > + last_used = (vq->last_used_idx) & (~(1 << VRING_PACKED_USED_INDEX_F_WRAP_CTR)); > id = le16_to_cpu(vq->packed.vring.desc[last_used].id); > *len = le32_to_cpu(vq->packed.vring.desc[last_used].len); > > @@ -1451,12 +1462,15 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > ret = vq->packed.desc_state[id].data; > detach_buf_packed(vq, id, ctx); > > - vq->last_used_idx += vq->packed.desc_state[id].num; > - if (unlikely(vq->last_used_idx >= vq->packed.vring.num)) { > - vq->last_used_idx -= vq->packed.vring.num; > - vq->packed.used_wrap_counter ^= 1; > + last_used += vq->packed.desc_state[id].num; > + if (unlikely(last_used >= vq->packed.vring.num)) {Can we tweak the math here to avoid the out of bound result?> + last_used -= vq->packed.vring.num; > + used_wrap_counter ^= 1; > } > > + last_used = (last_used | (used_wrap_counter << VRING_PACKED_DESC_F_USED)); > + vq->last_used_idx = last_used; > + > /* > * If we expect an interrupt for the next entry, tell host > * by writing event index and flush out the write before > @@ -1465,9 +1479,7 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DESC) > virtio_store_mb(vq->weak_barriers, > &vq->packed.vring.driver->off_wrap, > - cpu_to_le16(vq->last_used_idx | > - (vq->packed.used_wrap_counter << > - VRING_PACKED_EVENT_F_WRAP_CTR))); > + cpu_to_le16(vq->last_used_idx)); > > LAST_ADD_TIME_INVALID(vq); > > @@ -1499,9 +1511,7 @@ static unsigned int virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > > if (vq->event) { > vq->packed.vring.driver->off_wrap > - cpu_to_le16(vq->last_used_idx | > - (vq->packed.used_wrap_counter << > - VRING_PACKED_EVENT_F_WRAP_CTR)); > + cpu_to_le16(vq->last_used_idx); > /* > * We need to update event offset and event wrap > * counter first before updating event flags. > @@ -1518,8 +1528,7 @@ static unsigned int virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > } > > END_USE(vq); > - return vq->last_used_idx | ((u16)vq->packed.used_wrap_counter << > - VRING_PACKED_EVENT_F_WRAP_CTR); > + return vq->last_used_idx; > } > > static bool virtqueue_poll_packed(struct virtqueue *_vq, u16 off_wrap) > @@ -1550,9 +1559,9 @@ static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > if (vq->event) { > /* TODO: tune this threshold */ > bufs = (vq->packed.vring.num - vq->vq.num_free) * 3 / 4; > - wrap_counter = vq->packed.used_wrap_counter; > + wrap_counter = !!(vq->last_used_idx >> VRING_PACKED_USED_INDEX_F_WRAP_CTR); > > - used_idx = vq->last_used_idx + bufs; > + used_idx = (vq->last_used_idx & ~(1 << VRING_PACKED_USED_INDEX_F_WRAP_CTR)) + bufs; > if (used_idx >= vq->packed.vring.num) { > used_idx -= vq->packed.vring.num; > wrap_counter ^= 1; > @@ -1582,9 +1591,9 @@ static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > */ > virtio_mb(vq->weak_barriers); > > - if (is_used_desc_packed(vq, > - vq->last_used_idx, > - vq->packed.used_wrap_counter)) { > + wrap_counter = !!(vq->last_used_idx >> VRING_PACKED_USED_INDEX_F_WRAP_CTR); > + used_idx = (vq->last_used_idx & ~(1 << VRING_PACKED_USED_INDEX_F_WRAP_CTR)); > + if (is_used_desc_packed(vq, used_idx, wrap_counter)) { > END_USE(vq); > return false; > } > @@ -1689,7 +1698,7 @@ static struct virtqueue *vring_create_virtqueue_packed( > vq->notify = notify; > vq->weak_barriers = weak_barriers; > vq->broken = true; > - vq->last_used_idx = 0; > + vq->last_used_idx = 0 | (1 << VRING_PACKED_USED_INDEX_F_WRAP_CTR); > vq->event_triggered = false; > vq->num_added = 0; > vq->packed_ring = true; > @@ -1720,7 +1729,6 @@ static struct virtqueue *vring_create_virtqueue_packed( > > vq->packed.next_avail_idx = 0; > vq->packed.avail_wrap_counter = 1; > - vq->packed.used_wrap_counter = 1; > vq->packed.event_flags_shadow = 0; > vq->packed.avail_used_flags = 1 << VRING_PACKED_DESC_F_AVAIL; > > diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h > index 476d3e5c0fe7..96bcc4d52fce 100644 > --- a/include/uapi/linux/virtio_ring.h > +++ b/include/uapi/linux/virtio_ring.h > @@ -77,6 +77,12 @@ > */ > #define VRING_PACKED_EVENT_F_WRAP_CTR 15 > > + > +/* > + * used wrap Counter bit shift in vq->last_used_idx for packed ring > + */ > +#define VRING_PACKED_USED_INDEX_F_WRAP_CTR 15Let's simply reuse VRING_PACKED_EVENT_F_WRAP_CTR ? Thanks> + > /* We support indirect buffer descriptors */ > #define VIRTIO_RING_F_INDIRECT_DESC 28 > > -- > 2.31.1 >