Jason Wang
2022-Jun-15 03:40 UTC
[PATCH] virtio_ring : keep used_wrap_counter in vq->last_used_idx
On Wed, Jun 15, 2022 at 11:25 AM ?? <huangjie.albert at bytedance.com> wrote:> > Jason Wang <jasowang at redhat.com> ?2022?6?14??? 16:21??? > > > > On Tue, Jun 14, 2022 at 4:17 PM ?? <huangjie.albert at bytedance.com> wrote: > > > > > > Jason Wang <jasowang at redhat.com> ?2022?6?14??? 15:45??? > > > > > > > > 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. > > > > > > Yes, the idx pass to the is_used_desc_packed can never >> > > vq->packed.vring.num since we > > > tweak the math here : > > > >+ last_used += vq->packed.desc_state[id].num; > > > >+ if (unlikely(last_used >= vq->packed.vring.num)) { > > > >+ 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; > > > > > > > > > > > > + > > > > > 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? > > > > > > Yes, this can avoid the out of bound result. because of We just > > > assign last_used_idx in the following code? > > > vq->last_used_idx = last_used; > > > and it is a 16bit/32bit operations,and are guaranteed to be atomic > > > > > > > > > > > > + 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 15 > > > > > > > > Let's simply reuse VRING_PACKED_EVENT_F_WRAP_CTR ? > > > > > > > > Thanks > > > > > > Although the two values are the same, I see the meanings are different, > > > so I redefine one. Is it possible to rename > > > VRING_PACKED_EVENT_F_WRAP_CTR to VRING_PACKED_F_WRAP_CTR? > > > > > > Jason, what is your take? > > > > That looks even worse. So I'm fine to define a new macro as 15. > > > > Thanks > > > > > > > > > > > > > > + > > > > > /* We support indirect buffer descriptors */ > > > > > #define VIRTIO_RING_F_INDIRECT_DESC 28 > > > > > > > > > > -- > > > > > 2.31.1 > > > > > > > > > > > > > > > hello, Jason > > Any other suggestions?Looking at the current code again, it seems we've already used VRING_PACKED_EVENT_F_WRAP_CTR for packing information. see virtqueue_enable_cb_prepare_packed(): return vq->last_used_idx | ((u16)vq->packed.used_wrap_counter << VRING_PACKED_EVENT_F_WRAP_CTR); So I still prefer to simply use VRING_PACKED_EVENT_F_WRAP_CTR. Others should be fine. Thanks> I will do some stability and functional > testing before remaking a patch for patch v2. > > Thanks >