Date:   Fri, 19 Nov 2021 16:09:51 +0100
From:   Halil Pasic <pasic@linux.ibm.com>
To:     Jason Wang <jasowang@redhat.com>
Cc:     mst@redhat.com, virtualization@lists.linux-foundation.org,
        f.hetzelt@tu-berlin.de, linux-kernel@vger.kernel.org,
        david.kaplan@amd.com, konrad.wilk@oracle.com,
        Halil Pasic <pasic@linux.ibm.com>
Subject: Re: [PATCH V5 1/4] virtio_ring: validate used buffer length
Message-ID: <20211119160951.5f2294c8.pasic@linux.ibm.com>
In-Reply-To: <20211027022107.14357-2-jasowang@redhat.com>
References: <20211027022107.14357-1-jasowang@redhat.com>
        <20211027022107.14357-2-jasowang@redhat.com>
Organization: IBM
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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?

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.

If somebody is already working on this please reach out to me.

Regards,
Halil