2021-03-18 13:54:38

by Connor Kuehl

Subject: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size

From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors)
of the virtio spec:

"A driver MUST NOT create a descriptor chain longer than the Queue
Size of the device."

This text suggests that the warning should trigger even if
indirect descriptors are in use.

Reported-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Connor Kuehl <[email protected]>
---
drivers/virtio/virtio_ring.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71e16b53e9c1..1bc290f9ba13 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,

head = vq->free_head;

+ WARN_ON_ONCE(total_sg > vq->split.vring.num);
+
if (virtqueue_use_indirect(_vq, total_sg))
desc = alloc_indirect_split(_vq, total_sg, gfp);
else {
desc = NULL;
- WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
}

if (desc) {
@@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,

BUG_ON(total_sg == 0);

+ WARN_ON_ONCE(total_sg > vq->packed.vring.num);
+
if (virtqueue_use_indirect(_vq, total_sg))
return virtqueue_add_indirect_packed(vq, sgs, total_sg,
out_sgs, in_sgs, data, gfp);
@@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
head = vq->packed.next_avail_idx;
avail_used_flags = vq->packed.avail_used_flags;

- WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);
-
desc = vq->packed.vring.desc;
i = head;
descs_used = total_sg;
--
2.30.2

2021-03-22 03:25:26

by Jason Wang

Subject: Re: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size

?? 2021/3/18 ????9:52, Connor Kuehl д??:
> From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors)
> of the virtio spec:
>
> "A driver MUST NOT create a descriptor chain longer than the Queue
> Size of the device."
>
> This text suggests that the warning should trigger even if
> indirect descriptors are in use.


So I think at least the commit log needs some tweak.

For split virtqueue. We had:

2.6.5.2 Driver Requirements: The Virtqueue Descriptor Table

Drivers MUST NOT add a descriptor chain longer than 2^32 bytes in total;
this implies that loops in the descriptor chain are forbidden!

2.6.5.3.1 Driver Requirements: Indirect Descriptors

A driver MUST NOT create a descriptor chain longer than the Queue Size
of the device.

If I understand the spec correctly, the check is only needed for a
single indirect descriptor table?

For packed virtqueue. We had:

2.7.17 Driver Requirements: Scatter-Gather Support

A driver MUST NOT create a descriptor list longer than allowed by the
device.

A driver MUST NOT create a descriptor list longer than the Queue Size.

2.7.19 Driver Requirements: Indirect Descriptors

A driver MUST NOT create a descriptor chain longer than allowed by the
device.

So it looks to me the packed part is fine.

Note that if I understand the spec correctly 2.7.17 implies 2.7.19.

Thanks


>
> Reported-by: Stefan Hajnoczi <[email protected]>
> Signed-off-by: Connor Kuehl <[email protected]>
> ---
> drivers/virtio/virtio_ring.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 71e16b53e9c1..1bc290f9ba13 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>
> head = vq->free_head;
>
> + WARN_ON_ONCE(total_sg > vq->split.vring.num);
> +
> if (virtqueue_use_indirect(_vq, total_sg))
> desc = alloc_indirect_split(_vq, total_sg, gfp);
> else {
> desc = NULL;
> - WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
> }
>
> if (desc) {
> @@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>
> BUG_ON(total_sg == 0);
>
> + WARN_ON_ONCE(total_sg > vq->packed.vring.num);
> +
> if (virtqueue_use_indirect(_vq, total_sg))
> return virtqueue_add_indirect_packed(vq, sgs, total_sg,
> out_sgs, in_sgs, data, gfp);
> @@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
> head = vq->packed.next_avail_idx;
> avail_used_flags = vq->packed.avail_used_flags;
>
> - WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);
> -
> desc = vq->packed.vring.desc;
> i = head;
> descs_used = total_sg;

2021-03-22 08:21:26

by Michael S. Tsirkin

Subject: Re: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size

On Mon, Mar 22, 2021 at 11:22:15AM +0800, Jason Wang wrote:
>
> 在 2021/3/18 下午9:52, Connor Kuehl 写道:
> > From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors)
> > of the virtio spec:
> >
> > "A driver MUST NOT create a descriptor chain longer than the Queue
> > Size of the device."
> >
> > This text suggests that the warning should trigger even if
> > indirect descriptors are in use.
>
>
> So I think at least the commit log needs some tweak.
>
> For split virtqueue. We had:
>
> 2.6.5.2 Driver Requirements: The Virtqueue Descriptor Table
>
> Drivers MUST NOT add a descriptor chain longer than 2^32 bytes in total;
> this implies that loops in the descriptor chain are forbidden!
>
> 2.6.5.3.1 Driver Requirements: Indirect Descriptors
>
> A driver MUST NOT create a descriptor chain longer than the Queue Size of
> the device.
>
> If I understand the spec correctly, the check is only needed for a single
> indirect descriptor table?
>
> For packed virtqueue. We had:
>
> 2.7.17 Driver Requirements: Scatter-Gather Support
>
> A driver MUST NOT create a descriptor list longer than allowed by the
> device.
>
> A driver MUST NOT create a descriptor list longer than the Queue Size.
>
> 2.7.19 Driver Requirements: Indirect Descriptors
>
> A driver MUST NOT create a descriptor chain longer than allowed by the
> device.
>
> So it looks to me the packed part is fine.
>
> Note that if I understand the spec correctly 2.7.17 implies 2.7.19.
>
> Thanks

It would be quite strange for packed and split to differ here:
so for packed would you say there's no limit on # of descriptors at all?

I am guessing I just forgot to move this part from
the format specific to the common part of the spec.

This needs discussion in the TC mailing list - want to start a thread
there?



>
> >
> > Reported-by: Stefan Hajnoczi <[email protected]>
> > Signed-off-by: Connor Kuehl <[email protected]>
> > ---
> > drivers/virtio/virtio_ring.c | 7 ++++---
> > 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 71e16b53e9c1..1bc290f9ba13 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> > head = vq->free_head;
> > + WARN_ON_ONCE(total_sg > vq->split.vring.num);
> > +
> > if (virtqueue_use_indirect(_vq, total_sg))
> > desc = alloc_indirect_split(_vq, total_sg, gfp);
> > else {
> > desc = NULL;
> > - WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
> > }
> > if (desc) {
> > @@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
> > BUG_ON(total_sg == 0);
> > + WARN_ON_ONCE(total_sg > vq->packed.vring.num);
> > +
> > if (virtqueue_use_indirect(_vq, total_sg))
> > return virtqueue_add_indirect_packed(vq, sgs, total_sg,
> > out_sgs, in_sgs, data, gfp);
> > @@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
> > head = vq->packed.next_avail_idx;
> > avail_used_flags = vq->packed.avail_used_flags;
> > - WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);
> > -
> > desc = vq->packed.vring.desc;
> > i = head;
> > descs_used = total_sg;

2021-03-23 02:40:45

by Jason Wang

Subject: Re: [PATCH 1/3] virtio_ring: always warn when descriptor chain exceeds queue size

在 2021/3/22 下午4:17, Michael S. Tsirkin 写道:
> On Mon, Mar 22, 2021 at 11:22:15AM +0800, Jason Wang wrote:
>> 在 2021/3/18 下午9:52, Connor Kuehl 写道:
>>> From section 2.6.5.3.1 (Driver Requirements: Indirect Descriptors)
>>> of the virtio spec:
>>>
>>> "A driver MUST NOT create a descriptor chain longer than the Queue
>>> Size of the device."
>>>
>>> This text suggests that the warning should trigger even if
>>> indirect descriptors are in use.
>>
>> So I think at least the commit log needs some tweak.
>>
>> For split virtqueue. We had:
>>
>> 2.6.5.2 Driver Requirements: The Virtqueue Descriptor Table
>>
>> Drivers MUST NOT add a descriptor chain longer than 2^32 bytes in total;
>> this implies that loops in the descriptor chain are forbidden!
>>
>> 2.6.5.3.1 Driver Requirements: Indirect Descriptors
>>
>> A driver MUST NOT create a descriptor chain longer than the Queue Size of
>> the device.
>>
>> If I understand the spec correctly, the check is only needed for a single
>> indirect descriptor table?
>>
>> For packed virtqueue. We had:
>>
>> 2.7.17 Driver Requirements: Scatter-Gather Support
>>
>> A driver MUST NOT create a descriptor list longer than allowed by the
>> device.
>>
>> A driver MUST NOT create a descriptor list longer than the Queue Size.
>>
>> 2.7.19 Driver Requirements: Indirect Descriptors
>>
>> A driver MUST NOT create a descriptor chain longer than allowed by the
>> device.
>>
>> So it looks to me the packed part is fine.
>>
>> Note that if I understand the spec correctly 2.7.17 implies 2.7.19.
>>
>> Thanks
> It would be quite strange for packed and split to differ here:
> so for packed would you say there's no limit on # of descriptors at all?
>
> I am guessing I just forgot to move this part from
> the format specific to the common part of the spec.
>
> This needs discussion in the TC mailing list - want to start a thread
> there?


Will do.

Thanks


>
>
>
>>> Reported-by: Stefan Hajnoczi <[email protected]>
>>> Signed-off-by: Connor Kuehl <[email protected]>
>>> ---
>>> drivers/virtio/virtio_ring.c | 7 ++++---
>>> 1 file changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>>> index 71e16b53e9c1..1bc290f9ba13 100644
>>> --- a/drivers/virtio/virtio_ring.c
>>> +++ b/drivers/virtio/virtio_ring.c
>>> @@ -444,11 +444,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>>> head = vq->free_head;
>>> + WARN_ON_ONCE(total_sg > vq->split.vring.num);
>>> +
>>> if (virtqueue_use_indirect(_vq, total_sg))
>>> desc = alloc_indirect_split(_vq, total_sg, gfp);
>>> else {
>>> desc = NULL;
>>> - WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
>>> }
>>> if (desc) {
>>> @@ -1118,6 +1119,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>>> BUG_ON(total_sg == 0);
>>> + WARN_ON_ONCE(total_sg > vq->packed.vring.num);
>>> +
>>> if (virtqueue_use_indirect(_vq, total_sg))
>>> return virtqueue_add_indirect_packed(vq, sgs, total_sg,
>>> out_sgs, in_sgs, data, gfp);
>>> @@ -1125,8 +1128,6 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>>> head = vq->packed.next_avail_idx;
>>> avail_used_flags = vq->packed.avail_used_flags;
>>> - WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);
>>> -
>>> desc = vq->packed.vring.desc;
>>> i = head;
>>> descs_used = total_sg;