From a7722890fdfb2aaeb6b02d68bb0f1e411e58d539 Mon Sep 17 00:00:00 2001 From: "huangjie.albert" Date: Fri, 17 Jun 2022 10:04:11 +0800 Subject: virtio_ring : keep used_wrap_counter in vq->last_used_idx MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. v3->v4: - use READ_ONCE/WRITE_ONCE to get/set vq->last_used_idx v2->v3: - add inline function to get used_wrap_counter and last_used - when use vq->last_used_idx, only read once if vq->last_used_idx is read twice, the values can be inconsistent. - use last_used_idx & ~(-(1 << VRING_PACKED_EVENT_F_WRAP_CTR)) to get the all bits below VRING_PACKED_EVENT_F_WRAP_CTR v1->v2: - reuse the VRING_PACKED_EVENT_F_WRAP_CTR - Remove parameter judgment in is_used_desc_packed, because it can't be illegal Signed-off-by: huangjie.albert Message-Id: <20220617020411.80367-1-huangjie.albert@bytedance.com> Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_ring.c | 75 +++++++++++++++++++++++++++----------------- 1 file changed, 47 insertions(+), 28 deletions(-) (limited to 'drivers') diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 13a7348cedff..ef30465dd39c 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: + * bits up to VRING_PACKED_EVENT_F_WRAP_CTR include the last used index. + * bits from VRING_PACKED_EVENT_F_WRAP_CTR include the used wrap counter. + */ 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; @@ -973,6 +975,15 @@ static struct virtqueue *vring_create_virtqueue_split( /* * Packed ring specific functions - *_packed(). */ +static inline bool packed_used_wrap_counter(u16 last_used_idx) +{ + return !!(last_used_idx & (1 << VRING_PACKED_EVENT_F_WRAP_CTR)); +} + +static inline u16 packed_last_used(u16 last_used_idx) +{ + return last_used_idx & ~(-(1 << VRING_PACKED_EVENT_F_WRAP_CTR)); +} static void vring_unmap_extra_packed(const struct vring_virtqueue *vq, struct vring_desc_extra *extra) @@ -1406,8 +1417,14 @@ 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; + u16 last_used_idx; + bool used_wrap_counter; + + last_used_idx = READ_ONCE(vq->last_used_idx); + last_used = packed_last_used(last_used_idx); + used_wrap_counter = packed_used_wrap_counter(last_used_idx); + return is_used_desc_packed(vq, last_used, used_wrap_counter); } static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, @@ -1415,7 +1432,8 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, void **ctx) { struct vring_virtqueue *vq = to_vvq(_vq); - u16 last_used, id; + u16 last_used, id, last_used_idx; + bool used_wrap_counter; void *ret; START_USE(vq); @@ -1434,7 +1452,9 @@ 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; + last_used_idx = READ_ONCE(vq->last_used_idx); + used_wrap_counter = packed_used_wrap_counter(last_used_idx); + last_used = packed_last_used(last_used_idx); id = le16_to_cpu(vq->packed.vring.desc[last_used].id); *len = le32_to_cpu(vq->packed.vring.desc[last_used].len); @@ -1451,12 +1471,15 @@ 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)) { + last_used -= vq->packed.vring.num; + used_wrap_counter ^= 1; } + last_used = (last_used | (used_wrap_counter << VRING_PACKED_EVENT_F_WRAP_CTR)); + WRITE_ONCE(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 +1488,7 @@ 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 +1520,7 @@ 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 +1537,7 @@ 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) @@ -1537,7 +1555,7 @@ static bool virtqueue_poll_packed(struct virtqueue *_vq, u16 off_wrap) static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); - u16 used_idx, wrap_counter; + u16 used_idx, wrap_counter, last_used_idx; u16 bufs; START_USE(vq); @@ -1550,9 +1568,10 @@ 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; + last_used_idx = READ_ONCE(vq->last_used_idx); + wrap_counter = packed_used_wrap_counter(last_used_idx); - used_idx = vq->last_used_idx + bufs; + used_idx = packed_last_used(last_used_idx) + bufs; if (used_idx >= vq->packed.vring.num) { used_idx -= vq->packed.vring.num; wrap_counter ^= 1; @@ -1582,9 +1601,10 @@ 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)) { + last_used_idx = READ_ONCE(vq->last_used_idx); + wrap_counter = packed_used_wrap_counter(last_used_idx); + used_idx = packed_last_used(last_used_idx); + if (is_used_desc_packed(vq, used_idx, wrap_counter)) { END_USE(vq); return false; } @@ -1689,7 +1709,7 @@ 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_EVENT_F_WRAP_CTR); vq->event_triggered = false; vq->num_added = 0; vq->packed_ring = true; @@ -1720,7 +1740,6 @@ 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; -- cgit v1.2.3