Re: [PATCH] rpmsg: virtio: Fix broken rpmsg_probe()

From: Jason Wang
Date: Fri Jul 08 2022 - 02:19:45 EST

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On Wed, Jul 6, 2022 at 2:57 PM Arnaud POULIQUEN
<arnaud.pouliquen@xxxxxxxxxxx> wrote:
>
>
>
> On 7/6/22 06:03, Jason Wang wrote:
> > On Mon, Jul 4, 2022 at 5:45 PM Arnaud POULIQUEN
> > <arnaud.pouliquen@xxxxxxxxxxx> wrote:
> >>
> >> Hello Jason,
> >>
> >> On 7/4/22 06:35, Jason Wang wrote:
> >>> On Fri, Jul 1, 2022 at 2:16 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> >>>>
> >>>> On Fri, Jul 01, 2022 at 09:22:15AM +0800, Jason Wang wrote:
> >>>>> On Fri, Jul 1, 2022 at 3:20 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> >>>>>>
> >>>>>> On Thu, Jun 30, 2022 at 11:51:30AM -0600, Mathieu Poirier wrote:
> >>>>>>> + virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> >>>>>>> + jasowang@xxxxxxxxxx
> >>>>>>> + mst@xxxxxxxxxx
> >>>>>>>
> >>>>>>> On Thu, 30 Jun 2022 at 10:20, Arnaud POULIQUEN
> >>>>>>> <arnaud.pouliquen@xxxxxxxxxxx> wrote:
> >>>>>>>>
> >>>>>>>> Hi,
> >>>>>>>>
> >>>>>>>> On 6/29/22 19:43, Mathieu Poirier wrote:
> >>>>>>>>> Hi Anup,
> >>>>>>>>>
> >>>>>>>>> On Wed, Jun 08, 2022 at 10:43:34PM +0530, Anup Patel wrote:
> >>>>>>>>>> The rpmsg_probe() is broken at the moment because virtqueue_add_inbuf()
> >>>>>>>>>> fails due to both virtqueues (Rx and Tx) marked as broken by the
> >>>>>>>>>> __vring_new_virtqueue() function. To solve this, virtio_device_ready()
> >>>>>>>>>> (which unbreaks queues) should be called before virtqueue_add_inbuf().
> >>>>>>>>>>
> >>>>>>>>>> Fixes: 8b4ec69d7e09 ("virtio: harden vring IRQ")
> >>>>>>>>>> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> >>>>>>>>>> ---
> >>>>>>>>>> drivers/rpmsg/virtio_rpmsg_bus.c | 6 +++---
> >>>>>>>>>> 1 file changed, 3 insertions(+), 3 deletions(-)
> >>>>>>>>>>
> >>>>>>>>>> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
> >>>>>>>>>> index 905ac7910c98..71a64d2c7644 100644
> >>>>>>>>>> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> >>>>>>>>>> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> >>>>>>>>>> @@ -929,6 +929,9 @@ static int rpmsg_probe(struct virtio_device *vdev)
> >>>>>>>>>> /* and half is dedicated for TX */
> >>>>>>>>>> vrp->sbufs = bufs_va + total_buf_space / 2;
> >>>>>>>>>>
> >>>>>>>>>> + /* From this point on, we can notify and get callbacks. */
> >>>>>>>>>> + virtio_device_ready(vdev);
> >>>>>>>>>> +
> >>>>>>>>>
> >>>>>>>>> Calling virtio_device_ready() here means that virtqueue_get_buf_ctx_split() can
> >>>>>>>>> potentially be called (by way of rpmsg_recv_done()), which will race with
> >>>>>>>>> virtqueue_add_inbuf(). If buffers in the virtqueue aren't available then
> >>>>>>>>> rpmsg_recv_done() will fail, potentially breaking remote processors' state
> >>>>>>>>> machines that don't expect their initial name service to fail when the "device"
> >>>>>>>>> has been marked as ready.
> >>>>>>>>>
> >>>>>>>>> What does make me curious though is that nobody on the remoteproc mailing list
> >>>>>>>>> has complained about commit 8b4ec69d7e09 breaking their environment... By now,
> >>>>>>>>> i.e rc4, that should have happened. Anyone from TI, ST and Xilinx care to test this on
> >>>>>>>>> their rig?
> >>>>>>>>
> >>>>>>>> I tested on STm32mp1 board using tag v5.19-rc4(03c765b0e3b4)
> >>>>>>>> I confirm the issue!
> >>>>>>>>
> >>>>>>>> Concerning the solution, I share Mathieu's concern. This could break legacy.
> >>>>>>>> I made a short test and I would suggest to use __virtio_unbreak_device instead, tounbreak the virtqueues without changing the init sequence.
> >>>>>>>>
> >>>>>>>> I this case the patch would be:
> >>>>>>>>
> >>>>>>>> + /*
> >>>>>>>> + * Unbreak the virtqueues to allow to add buffers before setting the vdev status
> >>>>>>>> + * to ready
> >>>>>>>> + */
> >>>>>>>> + __virtio_unbreak_device(vdev);
> >>>>>>>> +
> >>>>>>>>
> >>>>>>>> /* set up the receive buffers */
> >>>>>>>> for (i = 0; i < vrp->num_bufs / 2; i++) {
> >>>>>>>> struct scatterlist sg;
> >>>>>>>> void *cpu_addr = vrp->rbufs + i * vrp->buf_size;
> >>>>>>>
> >>>>>>> This will indeed fix the problem. On the flip side the kernel
> >>>>>>> documentation for __virtio_unbreak_device() puzzles me...
> >>>>>>> It clearly states that it should be used for probing and restoring but
> >>>>>>> _not_ directly by the driver. Function rpmsg_probe() is part of
> >>>>>>> probing but also the entry point to a driver.
> >>>>>>>
> >>>>>>> Michael and virtualisation folks, is this the right way to move forward?
> >>>>>>
> >>>>>> I don't think it is, __virtio_unbreak_device is intended for core use.
> >>>>>
> >>>>> Can we fill the rx after virtio_device_ready() in this case?
> >>>>>
> >>>>> Btw, the driver set driver ok after registering, we probably get a svq
> >>>>> kick before DRIVER_OK?
> >>
> >> By "registering" you mean calling rpmsg_virtio_add_ctrl_dev and
> >> rpmsg_ns_register_device?
> >
> > Yes.
> >
> >>
> >> The rpmsg_ns_register_device has to be called before. Because it has to be
> >> probed to handle the first message coming from the remote side to create
> >> associated rpmsg local device.
> >
> > I couldn't find the code to do this, maybe you can give me some hint on this.
>
> The rpmsg_ns is available here :
> https://elixir.bootlin.com/linux/latest/source/drivers/rpmsg/rpmsg_ns.c
>
> It is probed on rpmsg_ns_register_device call.
> https://elixir.bootlin.com/linux/latest/source/drivers/rpmsg/virtio_rpmsg_bus.c#L974

Yes but what I want to ask is, it looks to me
rpmsg_ns_register_device() only creates a rpmsg device. Do you mean
the rpmsg driver that will handle the first message during its probe?

>
>
> >
> >> It doesn't send message.
> >
> > I see the function register the device to the bus, I wonder if this
> > means the device could be probed and used by the driver before
> > virtio_device_ready().
> >
> >>
> >> The risk could be for the rpmsg_ctrl device. Registering it
> >> after the virtio_device_ready(vdev) call could make sense...
> >
> > I see.
> >
> >>
> >>>>>
> >>>>> Thanks
> >>>>
> >>>> Is this an ack for the original patch?
> >>>
> >>> Nope, I meant, instead of moving virtio_device_ready() a little bit
> >>> earlier, can we only move the rvq filling after virtio_device_ready().
> >>>
> >>> Thanks
> >>
> >> Please find some concerns about this inversion here:
> >> https://lore.kernel.org/lkml/20220701053813-mutt-send-email-mst@xxxxxxxxxx/
> >>
> >> Regarding __virtio_unbreak_device. The pending virtio_break_device is
> >> used by some virtio driver.
> >> Could we consider that it makes sense to also have a
> >> virtio_unbreak_device interface?
> >
> > We don't want to allow the driver to unbreak a device since it's
> > easier to have bugs.
> >
> >>
> >>
> >> I do not well understand the reason of the commit:
> >> 8b4ec69d7e09 ("virtio: harden vring IRQ", 2022-05-27)
> >
> > It tries to forbid the virtqueue callbacks to be called before
> > virtio_device_ready(). This helps to prevent the malicious device from
> > attacking the driver.
> >
> > But unfortunately, it breaks several driver because:
> >
> > 1) some driver have races in probe/remove
> > 2) it tries to reuse vq->broken which may break the driver that call
> > virqueue_add() before virtio_device_ready() which is allowed by the
> > spec
> >
> > There's a discussion to have a better behavior that doesn't break the
> > existing drivers. And the IRQ hardening feature is marked as broken
> > now, so rpmsg should be fine without any extra effort.
>
> Thanks for the explanations.
> If the discussions are in a mail thread could you give me the reference?

Here're the discussions and commits:

https://lore.kernel.org/lkml/20220622012940.21441-1-jasowang@xxxxxxxxxx/

https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/commit/?h=linux-next&id=c346dae4f3fbce51bbd4f2ec5e8c6f9b91e93163
https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/commit/?h=linux-next&id=6a9720576cd00d30722c5f755bd17d4cfa9df636

Thanks

>
> Thanks,
> Arnaud
>
> >
> >> So following alternative is probably pretty naive:
> >> Is the use of virtqueue_disable_cb could be an alternative to the
> >> vq->broken usage allowing to register buffer while preventing virtqueue IRQ?
> >
> > Probably not, there's no guarantee that the device will not send
> > notification after virqtueue_disable_cb().
> >
> > Thanks
> >
> >>
> >> Thanks,
> >> Arnaud
> >>
> >>>
> >>>>
> >>>>>>
> >>>>>>>>
> >>>>>>>> Regards,
> >>>>>>>> Arnaud
> >>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Thanks,
> >>>>>>>>> Mathieu
> >>>>>>>>>
> >>>>>>>>>> /* set up the receive buffers */
> >>>>>>>>>> for (i = 0; i < vrp->num_bufs / 2; i++) {
> >>>>>>>>>> struct scatterlist sg;
> >>>>>>>>>> @@ -983,9 +986,6 @@ static int rpmsg_probe(struct virtio_device *vdev)
> >>>>>>>>>> */
> >>>>>>>>>> notify = virtqueue_kick_prepare(vrp->rvq);
> >>>>>>>>>>
> >>>>>>>>>> - /* From this point on, we can notify and get callbacks. */
> >>>>>>>>>> - virtio_device_ready(vdev);
> >>>>>>>>>> -
> >>>>>>>>>> /* tell the remote processor it can start sending messages */
> >>>>>>>>>> /*
> >>>>>>>>>> * this might be concurrent with callbacks, but we are only
> >>>>>>>>>> --
> >>>>>>>>>> 2.34.1
> >>>>>>>>>>
> >>>>>>
> >>>>
> >>>
> >>
> >
>

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