Re: [PATCH v2] rpmsg: virtio: don't let virtio core to validate used length

[Jason Wang]

On Thu, Nov 25, 2021 at 5:12 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Wed, Nov 24, 2021 at 05:20:45PM +0100, Arnaud Pouliquen wrote:
> > Using OpenAMP library on remote side, when the rpmsg framework tries to
> > reuse the buffer the following error message is displayed in
> > the virtqueue_get_buf_ctx_split function:
> > "virtio_rpmsg_bus virtio0: output:used len 28 is larger than in buflen 0"
> >
> > As described in virtio specification:
> > "many drivers ignored the len value, as a result, many devices set len
> > incorrectly. Thus, when using the legacy interface, it is generally
> > a good idea to ignore the len value in used ring entries if possible."
> >
> > To stay in compliance with the legacy libraries, this patch prevents the
> > virtio core from validating used length.
> >
> > Fixes: 939779f5152d ("virtio_ring: validate used buffer length")
> >
> > Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@xxxxxxxxxxx>
> > Cc: Jason Wang <jasowang@xxxxxxxxxx>
> > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > ---
>
> Arnaud, thanks a lot for the analysis.
>
> Jason, I think this is another good point. We really should not
> validate input for legacy devices at all.

I agree. Will do that in the next version.

Thanks

>
>
> > Update vs v1[1]: update commit message to clarify the context.
> >
> > base-commit: fa55b7dcdc43c1aa1ba12bca9d2dd4318c2a0dbf
> >
> > [1]https://lore.kernel.org/lkml/20211122160812.25125-1-arnaud.pouliquen@xxxxxxxxxxx/T/
> > ---
> >  drivers/rpmsg/virtio_rpmsg_bus.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
> > index 9c112aa65040..5f73f19c2c38 100644
> > --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> > +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> > @@ -1054,6 +1054,7 @@ static struct virtio_driver virtio_ipc_driver = {
> >       .feature_table_size = ARRAY_SIZE(features),
> >       .driver.name    = KBUILD_MODNAME,
> >       .driver.owner   = THIS_MODULE,
> > +     .suppress_used_validation = true,
> >       .id_table       = id_table,
> >       .probe          = rpmsg_probe,
> >       .remove         = rpmsg_remove,
> > --
> > 2.17.1
>