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

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Date:   Thu, 2 Dec 2021 10:00:11 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        linux-remoteproc@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2] rpmsg: virtio: don't let virtio core to validate used
 length

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@...hat.com> 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@...s.st.com>
> > > Cc: Jason Wang <jasowang@...hat.com>
> > > Cc: Michael S. Tsirkin <mst@...hat.com>
> > > ---
> >
> > 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?

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@foss.st.com/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
> >
>