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

[Jason Wang]

On Fri, Dec 3, 2021 at 1:00 AM Mathieu Poirier
<mathieu.poirier@xxxxxxxxxx> wrote:
>
> Hey guys,
>
> On Thu, Nov 25, 2021 at 10:15:44AM +0800, Jason Wang wrote:
> > 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.
>
> I'm a little unclear about the "next version" in the above comment - is this
> something I should wait for?  Should I move forward with Arnaud's patch?

Just to make it clear. If my understanding is correct, my series was
reverted so this patch is not needed.

For "next version", I meant I will resend the new version of used
length validation that

- only do the validation when it was explicitly enabled
- warn instead of bug
- do not validate legacy device

Thanks

>
> Thanks,
> Mathieu
>
> >
> > 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
> > >
> >
>