Re: [PATCH V5 1/4] virtio_ring: validate used buffer length

Stefano Garzarella
2021-11-22T07:42:54Z

On Mon, Nov 22, 2021 at 11:51:09AM +0800, Jason Wang wrote:
>On Fri, Nov 19, 2021 at 11:10 PM Halil Pasic <pasic@linux.ibm.com> wrote:
>>
>> On Wed, 27 Oct 2021 10:21:04 +0800
>> Jason Wang <jasowang@redhat.com> wrote:
>>
>> > This patch validate the used buffer length provided by the device
>> > before trying to use it. This is done by record the in buffer length
>> > in a new field in desc_state structure during virtqueue_add(), then we
>> > can fail the virtqueue_get_buf() when we find the device is trying to
>> > give us a used buffer length which is greater than the in buffer
>> > length.
>> >
>> > Since some drivers have already done the validation by themselves,
>> > this patch tries to makes the core validation optional. For the driver
>> > that doesn't want the validation, it can set the
>> > suppress_used_validation to be true (which could be overridden by
>> > force_used_validation module parameter). To be more efficient, a
>> > dedicate array is used for storing the validate used length, this
>> > helps to eliminate the cache stress if validation is done by the
>> > driver.
>> >
>> > Signed-off-by: Jason Wang <jasowang@redhat.com>
>>
>> Hi Jason!
>>
>> Our CI has detected, that virtio-vsock became unusable with this
>> patch on s390x. I didn't test on x86 yet. The guest kernel says
>> something like:
>> vmw_vsock_virtio_transport virtio1: tx: used len 44 is larger than in buflen 0
>>
>> Did you, or anybody else, see something like this on platforms other that
>> s390x?
>
>Adding Stefan and Stefano.
>
>I think it should be a common issue, looking at

Yep, I confirm the same behaviour on x86_64. On Friday evening I had the
same failure while testing latest QEMU and Linux kernel.

>vhost_vsock_handle_tx_kick(), it did:
>
>len += sizeof(pkt->hdr);
>vhost_add_used(vq, head, len);
>
>which looks like a violation of the spec since it's TX.
>
>>
>> I had a quick look at this code, and I speculate that it probably
>> uncovers a pre-existig bug, rather than introducing a new one.
>
>I agree.
>
>>
>> If somebody is already working on this please reach out to me.
>

My plan was to debug and test it today, so let me know if you need some
help.

>AFAIK, no. I think the plan is to fix both the device and drive side
>(but I'm not sure we need a new feature for this if we stick to the
>validation).
>

Yes, maybe we need a new feature, since I believe there has been this
problem since the beginning.

Thanks,
Stefano