[1/1] vhost: fix a double fetch when dequeue offloading
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Commit Message
The hdr->csum_start does two successive reads from user space to read a
variable length data structure. The result overflow if the data structure
changes between the two reads.
To fix this, we can prevent double fetch issue by copying virtio_hdr to
the temporary variable.
Fixes: 4dc4e33ffa10 ("net/virtio: fix Rx checksum calculation")
Cc: stable@dpdk.org
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
---
lib/vhost/virtio_net.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
Comments
On Thu, Dec 19, 2024 at 7:38 AM Yunjian Wang <wangyunjian@huawei.com> wrote:
>
> The hdr->csum_start does two successive reads from user space to read a
> variable length data structure. The result overflow if the data structure
> changes between the two reads.
>
> To fix this, we can prevent double fetch issue by copying virtio_hdr to
> the temporary variable.
>
> Fixes: 4dc4e33ffa10 ("net/virtio: fix Rx checksum calculation")
> Cc: stable@dpdk.org
>
> Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> ---
> lib/vhost/virtio_net.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 69901ab3b5..5c40ae7069 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -2914,10 +2914,12 @@ desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
> * in a contiguous virtual area.
> */
> copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
> - hdr = &tmp_hdr;
> } else {
> - hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
> + rte_memcpy((void *)(uintptr_t)&tmp_hdr,
> + (void *)(uintptr_t)buf_vec[0].buf_addr,
> + sizeof(struct virtio_net_hdr));
> }
> + hdr = &tmp_hdr;
> }
This will need some benchmark, as I remember putting rte_memcpy in
inlined helpers had some performance impact.
Instead, I would call copy_vnet_hdr_from_desc unconditionnally, and
store in a struct virtio_net_hdr hdr variable (+ a has_vnet_hdr
boolean to indicate validity).
Something like:
if (virtio_net_with_host_offload(dev)) {
- if (unlikely(buf_vec[0].buf_len < sizeof(struct
virtio_net_hdr))) {
- /*
- * No luck, the virtio-net header doesn't fit
- * in a contiguous virtual area.
- */
- copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
- hdr = &tmp_hdr;
- } else {
- hdr = (struct virtio_net_hdr
*)((uintptr_t)buf_vec[0].buf_addr);
- }
+ copy_vnet_hdr_from_desc(&hdr, buf_vec);
+ has_vnet_hdr = true;
}
(besides, in copy_vnet_hdr_from_desc, the while (cond) {} loop could
be changed to do a do {} while (cond), and that approach requires
performance numbers too)
>
> for (vec_idx = 0; vec_idx < nr_vec; vec_idx++) {
> @@ -3363,7 +3365,7 @@ virtio_dev_tx_batch_packed(struct virtio_net *dev,
> {
> uint16_t avail_idx = vq->last_avail_idx;
> uint32_t buf_offset = sizeof(struct virtio_net_hdr_mrg_rxbuf);
> - struct virtio_net_hdr *hdr;
> + struct virtio_net_hdr hdr;
> uintptr_t desc_addrs[PACKED_BATCH_SIZE];
> uint16_t ids[PACKED_BATCH_SIZE];
> uint16_t i;
> @@ -3382,8 +3384,9 @@ virtio_dev_tx_batch_packed(struct virtio_net *dev,
>
> if (virtio_net_with_host_offload(dev)) {
> vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> - hdr = (struct virtio_net_hdr *)(desc_addrs[i]);
> - vhost_dequeue_offload(dev, hdr, pkts[i], legacy_ol_flags);
> + rte_memcpy((void *)(uintptr_t)&hdr,
> + (void *)(uintptr_t)desc_addrs[i], sizeof(struct virtio_net_hdr));
> + vhost_dequeue_offload(dev, &hdr, pkts[i], legacy_ol_flags);
> }
> }
Here too, there may be an impact with adding rte_memcpy.
Just do a copy like:
if (virtio_net_with_host_offload(dev)) {
+ struct virtio_net_hdr hdr;
+
vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
- hdr = (struct virtio_net_hdr *)(desc_addrs[i]);
- vhost_dequeue_offload(dev, hdr, pkts[i],
legacy_ol_flags);
+ hdr = *(struct virtio_net_hdr *)(desc_addrs[i]);
+ vhost_dequeue_offload(dev, &hdr, pkts[i],
legacy_ol_flags);
}
> -----Original Message-----
> From: David Marchand [mailto:david.marchand@redhat.com]
> Sent: Thursday, December 19, 2024 4:24 PM
> To: Wangyunjian(wangyunjian,TongTu) <wangyunjian@huawei.com>;
> maxime.coquelin@redhat.com
> Cc: dev@dpdk.org; chenbox@nvidia.com; Lilijun (Jerry)
> <jerry.lilijun@huawei.com>; xiawei (H) <xiawei40@huawei.com>;
> wangzengyuan <wangzengyuan@huawei.com>; stable@dpdk.org
> Subject: Re: [PATCH 1/1] vhost: fix a double fetch when dequeue offloading
>
> On Thu, Dec 19, 2024 at 7:38 AM Yunjian Wang <wangyunjian@huawei.com>
> wrote:
> >
> > The hdr->csum_start does two successive reads from user space to read a
> > variable length data structure. The result overflow if the data structure
> > changes between the two reads.
> >
> > To fix this, we can prevent double fetch issue by copying virtio_hdr to
> > the temporary variable.
> >
> > Fixes: 4dc4e33ffa10 ("net/virtio: fix Rx checksum calculation")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> > ---
> > lib/vhost/virtio_net.c | 13 ++++++++-----
> > 1 file changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> > index 69901ab3b5..5c40ae7069 100644
> > --- a/lib/vhost/virtio_net.c
> > +++ b/lib/vhost/virtio_net.c
> > @@ -2914,10 +2914,12 @@ desc_to_mbuf(struct virtio_net *dev, struct
> vhost_virtqueue *vq,
> > * in a contiguous virtual area.
> > */
> > copy_vnet_hdr_from_desc(&tmp_hdr,
> buf_vec);
> > - hdr = &tmp_hdr;
> > } else {
> > - hdr = (struct virtio_net_hdr
> *)((uintptr_t)buf_vec[0].buf_addr);
> > + rte_memcpy((void *)(uintptr_t)&tmp_hdr,
> > + (void
> *)(uintptr_t)buf_vec[0].buf_addr,
> > + sizeof(struct virtio_net_hdr));
> > }
> > + hdr = &tmp_hdr;
> > }
>
> This will need some benchmark, as I remember putting rte_memcpy in
> inlined helpers had some performance impact.
>
> Instead, I would call copy_vnet_hdr_from_desc unconditionnally, and
> store in a struct virtio_net_hdr hdr variable (+ a has_vnet_hdr
> boolean to indicate validity).
> Something like:
> if (virtio_net_with_host_offload(dev)) {
> - if (unlikely(buf_vec[0].buf_len < sizeof(struct
> virtio_net_hdr))) {
> - /*
> - * No luck, the virtio-net header doesn't fit
> - * in a contiguous virtual area.
> - */
> - copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
> - hdr = &tmp_hdr;
> - } else {
> - hdr = (struct virtio_net_hdr
> *)((uintptr_t)buf_vec[0].buf_addr);
> - }
> + copy_vnet_hdr_from_desc(&hdr, buf_vec);
> + has_vnet_hdr = true;
> }
>
> (besides, in copy_vnet_hdr_from_desc, the while (cond) {} loop could
> be changed to do a do {} while (cond), and that approach requires
> performance numbers too)
How about this?
@@ -2904,8 +2904,8 @@ desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
uint32_t hdr_remain = dev->vhost_hlen;
uint32_t cpy_len;
struct rte_mbuf *cur = m, *prev = m;
- struct virtio_net_hdr tmp_hdr;
- struct virtio_net_hdr *hdr = NULL;
+ bool has_vnet_hdr = false;
+ struct virtio_net_hdr hdr;
uint16_t vec_idx;
struct vhost_async *async = vq->async;
struct async_inflight_info *pkts_info;
@@ -2921,11 +2921,11 @@ desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
* No luck, the virtio-net header doesn't fit
* in a contiguous virtual area.
*/
- copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
- hdr = &tmp_hdr;
+ copy_vnet_hdr_from_desc(&hdr, buf_vec);
} else {
- hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
+ hdr = *(struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
}
+ has_vnet_hdr = true;
}
>
>
> >
> > for (vec_idx = 0; vec_idx < nr_vec; vec_idx++) {
> > @@ -3363,7 +3365,7 @@ virtio_dev_tx_batch_packed(struct virtio_net
> *dev,
> > {
> > uint16_t avail_idx = vq->last_avail_idx;
> > uint32_t buf_offset = sizeof(struct virtio_net_hdr_mrg_rxbuf);
> > - struct virtio_net_hdr *hdr;
> > + struct virtio_net_hdr hdr;
> > uintptr_t desc_addrs[PACKED_BATCH_SIZE];
> > uint16_t ids[PACKED_BATCH_SIZE];
> > uint16_t i;
> > @@ -3382,8 +3384,9 @@ virtio_dev_tx_batch_packed(struct virtio_net
> *dev,
> >
> > if (virtio_net_with_host_offload(dev)) {
> > vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> > - hdr = (struct virtio_net_hdr *)(desc_addrs[i]);
> > - vhost_dequeue_offload(dev, hdr, pkts[i],
> legacy_ol_flags);
> > + rte_memcpy((void *)(uintptr_t)&hdr,
> > + (void *)(uintptr_t)desc_addrs[i],
> sizeof(struct virtio_net_hdr));
> > + vhost_dequeue_offload(dev, &hdr, pkts[i],
> legacy_ol_flags);
> > }
> > }
>
> Here too, there may be an impact with adding rte_memcpy.
> Just do a copy like:
>
> if (virtio_net_with_host_offload(dev)) {
> + struct virtio_net_hdr hdr;
> +
> vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> - hdr = (struct virtio_net_hdr *)(desc_addrs[i]);
> - vhost_dequeue_offload(dev, hdr, pkts[i],
> legacy_ol_flags);
> + hdr = *(struct virtio_net_hdr *)(desc_addrs[i]);
> + vhost_dequeue_offload(dev, &hdr, pkts[i],
> legacy_ol_flags);
> }
>
Thanks for your suggestion, will include them in next version.
>
> --
> David Marchand
>
On Thu, 19 Dec 2024 14:38:28 +0800
Yunjian Wang <wangyunjian@huawei.com> wrote:
> - hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
> + rte_memcpy((void *)(uintptr_t)&tmp_hdr,
> + (void *)(uintptr_t)buf_vec[0].buf_addr,
> + sizeof(struct virtio_net_hdr));
> }
Do not introduce more rte_memcpy of a fixed size.
You don't need that many casts!
Why can you not use a structure assignment here.
> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Friday, December 20, 2024 12:16 AM
> To: Wangyunjian(wangyunjian,TongTu) <wangyunjian@huawei.com>
> Cc: dev@dpdk.org; maxime.coquelin@redhat.com; chenbox@nvidia.com;
> Lilijun (Jerry) <jerry.lilijun@huawei.com>; xiawei (H) <xiawei40@huawei.com>;
> wangzengyuan <wangzengyuan@huawei.com>; stable@dpdk.org
> Subject: Re: [PATCH 1/1] vhost: fix a double fetch when dequeue offloading
>
> On Thu, 19 Dec 2024 14:38:28 +0800
> Yunjian Wang <wangyunjian@huawei.com> wrote:
>
> > - hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
> > + rte_memcpy((void *)(uintptr_t)&tmp_hdr,
> > + (void *)(uintptr_t)buf_vec[0].buf_addr,
> > + sizeof(struct virtio_net_hdr));
> > }
>
> Do not introduce more rte_memcpy of a fixed size.
> You don't need that many casts!
> Why can you not use a structure assignment here.
The virtio_hdr is a shared component, and other fields within it are read
multiple times. This can potentially result in a double fetch scenario.
On Fri, 20 Dec 2024 02:17:12 +0000
"Wangyunjian(wangyunjian,TongTu)" <wangyunjian@huawei.com> wrote:
> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > Sent: Friday, December 20, 2024 12:16 AM
> > To: Wangyunjian(wangyunjian,TongTu) <wangyunjian@huawei.com>
> > Cc: dev@dpdk.org; maxime.coquelin@redhat.com; chenbox@nvidia.com;
> > Lilijun (Jerry) <jerry.lilijun@huawei.com>; xiawei (H) <xiawei40@huawei.com>;
> > wangzengyuan <wangzengyuan@huawei.com>; stable@dpdk.org
> > Subject: Re: [PATCH 1/1] vhost: fix a double fetch when dequeue offloading
> >
> > On Thu, 19 Dec 2024 14:38:28 +0800
> > Yunjian Wang <wangyunjian@huawei.com> wrote:
> >
> > > - hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
> > > + rte_memcpy((void *)(uintptr_t)&tmp_hdr,
> > > + (void *)(uintptr_t)buf_vec[0].buf_addr,
> > > + sizeof(struct virtio_net_hdr));
> > > }
> >
> > Do not introduce more rte_memcpy of a fixed size.
> > You don't need that many casts!
> > Why can you not use a structure assignment here.
>
> The virtio_hdr is a shared component, and other fields within it are read
> multiple times. This can potentially result in a double fetch scenario.
The point is do a copy, but not with rte_memcpy.
Also you need a rte_compiler_barrier() anyway.
On Thu, 19 Dec 2024 14:38:28 +0800
Yunjian Wang <wangyunjian@huawei.com> wrote:
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 69901ab3b5..5c40ae7069 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -2914,10 +2914,12 @@ desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
> * in a contiguous virtual area.
> */
> copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
> - hdr = &tmp_hdr;
> } else {
> - hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
> + rte_memcpy((void *)(uintptr_t)&tmp_hdr,
> + (void *)(uintptr_t)buf_vec[0].buf_addr,
> + sizeof(struct virtio_net_hdr));
> }
> + hdr = &tmp_hdr;
Since this if block is just an optimization of the case where vnet header
is contiguous why not just always use copy_vnet_hdr_from_desc? and inline it?
> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Saturday, December 21, 2024 12:36 AM
> To: Wangyunjian(wangyunjian,TongTu) <wangyunjian@huawei.com>
> Cc: dev@dpdk.org; maxime.coquelin@redhat.com; chenbox@nvidia.com;
> Lilijun (Jerry) <jerry.lilijun@huawei.com>; xiawei (H) <xiawei40@huawei.com>;
> wangzengyuan <wangzengyuan@huawei.com>; stable@dpdk.org
> Subject: Re: [PATCH 1/1] vhost: fix a double fetch when dequeue offloading
>
> On Thu, 19 Dec 2024 14:38:28 +0800
> Yunjian Wang <wangyunjian@huawei.com> wrote:
>
> > diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> > index 69901ab3b5..5c40ae7069 100644
> > --- a/lib/vhost/virtio_net.c
> > +++ b/lib/vhost/virtio_net.c
> > @@ -2914,10 +2914,12 @@ desc_to_mbuf(struct virtio_net *dev, struct
> vhost_virtqueue *vq,
> > * in a contiguous virtual area.
> > */
> > copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
> > - hdr = &tmp_hdr;
> > } else {
> > - hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
> > + rte_memcpy((void *)(uintptr_t)&tmp_hdr,
> > + (void *)(uintptr_t)buf_vec[0].buf_addr,
> > + sizeof(struct virtio_net_hdr));
> > }
> > + hdr = &tmp_hdr;
>
> Since this if block is just an optimization of the case where vnet header
> is contiguous why not just always use copy_vnet_hdr_from_desc? and inline it?
I also considered using the copy_vnet_hdr_from_desc function directly.
However, in most cases, the vnet header is continuous, and reusing
copy_vnet_hdr_from_desc results in additional operations.
Thanks,
Yunjian
@@ -2914,10 +2914,12 @@ desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
* in a contiguous virtual area.
*/
copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
- hdr = &tmp_hdr;
} else {
- hdr = (struct virtio_net_hdr *)((uintptr_t)buf_vec[0].buf_addr);
+ rte_memcpy((void *)(uintptr_t)&tmp_hdr,
+ (void *)(uintptr_t)buf_vec[0].buf_addr,
+ sizeof(struct virtio_net_hdr));
}
+ hdr = &tmp_hdr;
}
for (vec_idx = 0; vec_idx < nr_vec; vec_idx++) {
@@ -3363,7 +3365,7 @@ virtio_dev_tx_batch_packed(struct virtio_net *dev,
{
uint16_t avail_idx = vq->last_avail_idx;
uint32_t buf_offset = sizeof(struct virtio_net_hdr_mrg_rxbuf);
- struct virtio_net_hdr *hdr;
+ struct virtio_net_hdr hdr;
uintptr_t desc_addrs[PACKED_BATCH_SIZE];
uint16_t ids[PACKED_BATCH_SIZE];
uint16_t i;
@@ -3382,8 +3384,9 @@ virtio_dev_tx_batch_packed(struct virtio_net *dev,
if (virtio_net_with_host_offload(dev)) {
vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
- hdr = (struct virtio_net_hdr *)(desc_addrs[i]);
- vhost_dequeue_offload(dev, hdr, pkts[i], legacy_ol_flags);
+ rte_memcpy((void *)(uintptr_t)&hdr,
+ (void *)(uintptr_t)desc_addrs[i], sizeof(struct virtio_net_hdr));
+ vhost_dequeue_offload(dev, &hdr, pkts[i], legacy_ol_flags);
}
}