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Tsirkin" To: Albert Huang Subject: Re: [PATCH v3] virtio_ring : keep used_wrap_counter in vq->last_used_idx Message-ID: <20220616081812-mutt-send-email-mst@kernel.org> References: <20220616024148-mutt-send-email-mst@kernel.org> <20220616095500.41239-1-huangjie.albert@bytedance.com> MIME-Version: 1.0 In-Reply-To: <20220616095500.41239-1-huangjie.albert@bytedance.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: linux-kernel@vger.kernel.org, yuanzhu@bytedance.com, virtualization@lists.linux-foundation.org X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: virtualization-bounces@lists.linux-foundation.org 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([2a03:c5c0:107d:d500:e9ae:3150:6c35:ac38]) by smtp.gmail.com with ESMTPSA id i2-20020adffdc2000000b00213ba4b5d94sm2135823wrs.27.2022.06.16.05.21.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Jun 2022 05:21:29 -0700 (PDT) Date: Thu, 16 Jun 2022 08:21:25 -0400 From: "Michael S. Tsirkin" To: Albert Huang Cc: yuanzhu@bytedance.com, Jason Wang , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] virtio_ring : keep used_wrap_counter in vq->last_used_idx Message-ID: <20220616081812-mutt-send-email-mst@kernel.org> References: <20220616024148-mutt-send-email-mst@kernel.org> <20220616095500.41239-1-huangjie.albert@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220616095500.41239-1-huangjie.albert@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 16, 2022 at 05:54:59PM +0800, Albert Huang wrote: > From: "huangjie.albert" > > 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. > > 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 > --- > drivers/virtio/virtio_ring.c | 75 ++++++++++++++++++++++-------------- > 1 file changed, 47 insertions(+), 28 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 13a7348cedff..a253f50b8f86 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_EVENT_F_WRAP_CTR is > + * the bit shift in last_used_idx reword: 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 = 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 = vq->last_used_idx; I think we need READ_ONCE here. Otherwise compiler is free to still do two reads. > + 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)); > + 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 = 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 = vq->last_used_idx; same here. > + 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; > > -- > 2.31.1