diff mbox series

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

Message ID 20210318135223.1342795-2-ckuehl@redhat.com (mailing list archive)
State New
Headers show
Series virtiofs: split requests that exceed virtqueue size | expand

Commit Message

Connor Kuehl March 18, 2021, 1:52 p.m. UTC
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 <stefanha@redhat.com>
Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
---
 drivers/virtio/virtio_ring.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Comments

Jason Wang March 22, 2021, 3:22 a.m. UTC | #1
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


>
> Reported-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> ---
>   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;
Michael S. Tsirkin March 22, 2021, 8:17 a.m. UTC | #2
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 <stefanha@redhat.com>
> > Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> > ---
> >   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;
Jason Wang March 23, 2021, 2:38 a.m. UTC | #3
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 <stefanha@redhat.com>
>>> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
>>> ---
>>>    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;
diff mbox series

Patch

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;