Virtualization - Nov 2022 - [PATCH 0/4] Fix probe failed when modprobe modules

On Mon, Nov 28, 2022 at 10:10:01AM +0800, Li Zetao
wrote:
> This patchset fixes similar issue, the root cause of the
> problem is that the virtqueues are not stopped on error
> handling path.
I've been thinking about this.
Almost all drivers are affected.

The reason really is that it used to be the right thing to do:
On legacy pci del_vqs writes 0
into vq index and this resets the device as a side effect
(we actually do this multiple times, what e.g. writes of MSI vector
 after the 1st reset do I have no idea).

mmio ccw and modern pci don't.

Given this has been with us for a while I am inlined to look for
a global solution rather than tweaking each driver.

Given many drivers are supposed to work on legacy too, we know del_vqs
includes a reset for many of them. So I think I see a better way to do
this:

Add virtio_reset_device_and_del_vqs()

and convert all drivers to that.

When doing this, we also need to/can fix a related problem (and related
to the hardening that Jason Wang was looking into):
virtio_reset_device is inherently racy: vq interrupts could
be in flight when we do reset. We need to prevent handlers from firing in
the window between reset and freeing the irq, so we should first
free irqs and only then start changing the state by e.g.
device reset.


Quite a lot of core work here. Jason are you still looking into
hardening?


> Li Zetao (4):
>   9p: Fix probe failed when modprobe 9pnet_virtio
>   virtio-mem: Fix probe failed when modprobe virtio_mem
>   virtio-input: Fix probe failed when modprobe virtio_input
>   virtio-blk: Fix probe failed when modprobe virtio_blk
> 
>  drivers/block/virtio_blk.c    | 1 +
>  drivers/virtio/virtio_input.c | 1 +
>  drivers/virtio/virtio_mem.c   | 1 +
>  net/9p/trans_virtio.c         | 1 +
>  4 files changed, 4 insertions(+)
> 
> -- 
> 2.25.1

On Mon, Nov 28, 2022 at 6:14 PM Michael S. Tsirkin <mst at redhat.com>
wrote:
>
> On Mon, Nov 28, 2022 at 10:10:01AM +0800, Li Zetao wrote:
> > This patchset fixes similar issue, the root cause of the
> > problem is that the virtqueues are not stopped on error
> > handling path.
>
> I've been thinking about this.
> Almost all drivers are affected.
>
> The reason really is that it used to be the right thing to do:
> On legacy pci del_vqs writes 0
> into vq index
into vq address actually?
> and this resets the device as a side effect
I think there's no guarantee for a device to do this.
> (we actually do this multiple times, what e.g. writes of MSI vector
>  after the 1st reset do I have no idea).
>
> mmio ccw and modern pci don't.
>
> Given this has been with us for a while I am inlined to look for
> a global solution rather than tweaking each driver.
But do we still need patches for -stable at least?
>
> Given many drivers are supposed to work on legacy too, we know del_vqs
> includes a reset for many of them. So I think I see a better way to do
> this:
>
> Add virtio_reset_device_and_del_vqs()
What's the difference with the current del_vqs method? Is this something
like:

virtio_reset_device();
config->del_vqs();
>
> and convert all drivers to that.
>
> When doing this, we also need to/can fix a related problem (and related
> to the hardening that Jason Wang was looking into):
> virtio_reset_device is inherently racy: vq interrupts could
> be in flight when we do reset. We need to prevent handlers from firing in
> the window between reset and freeing the irq, so we should first
> free irqs and only then start changing the state by e.g.
> device reset.
Yes.
>
>
> Quite a lot of core work here. Jason are you still looking into
> hardening?
Yes, last time we've discussed a solution that depends on the first
kick to enable the interrupt handler. But after some thought, it seems
risky since there's no guarantee that the device work in this way.

One example is the current vhost_net, it doesn't wait for the kick to
process the rx packets. Any more thought on this?

Thanks

>
>
>
> > Li Zetao (4):
> >   9p: Fix probe failed when modprobe 9pnet_virtio
> >   virtio-mem: Fix probe failed when modprobe virtio_mem
> >   virtio-input: Fix probe failed when modprobe virtio_input
> >   virtio-blk: Fix probe failed when modprobe virtio_blk
> >
> >  drivers/block/virtio_blk.c    | 1 +
> >  drivers/virtio/virtio_input.c | 1 +
> >  drivers/virtio/virtio_mem.c   | 1 +
> >  net/9p/trans_virtio.c         | 1 +
> >  4 files changed, 4 insertions(+)
> >
> > --
> > 2.25.1
>

On Tue, Nov 29, 2022 at 11:37:09AM +0800, Jason Wang
wrote:
> >
> >
> > Quite a lot of core work here. Jason are you still looking into
> > hardening?
> 
> Yes, last time we've discussed a solution that depends on the first
> kick to enable the interrupt handler. But after some thought, it seems
> risky since there's no guarantee that the device work in this way.
> 
> One example is the current vhost_net, it doesn't wait for the kick to
> process the rx packets. Any more thought on this?
> 
> Thanks
Specifically virtio net is careful to call virtio_device_ready
under rtnl lock so buffers are only added after DRIVER_OK.

However we do not need to tie this to kick, this is what I wrote:
> BTW Jason, I had the idea to disable callbacks until driver uses the
> virtio core for the first time (e.g. by calling virtqueue_add* family of
> APIs). Less aggressive than your ideas but I feel it will add security
> to the init path at least.
So not necessarily kick, we can make adding buffers allow the
interrupt.



-- 
MST

On Mon, Nov 28, 2022 at 05:14:44AM -0500, Michael S. Tsirkin
wrote:
> On Mon, Nov 28, 2022 at 10:10:01AM +0800, Li Zetao wrote:
> > This patchset fixes similar issue, the root cause of the
> > problem is that the virtqueues are not stopped on error
> > handling path.
> 
> I've been thinking about this.
> Almost all drivers are affected.
> 
> The reason really is that it used to be the right thing to do:
> On legacy pci del_vqs writes 0
> into vq index and this resets the device as a side effect
> (we actually do this multiple times, what e.g. writes of MSI vector
>  after the 1st reset do I have no idea).
> 
> mmio ccw and modern pci don't.
> 
> Given this has been with us for a while I am inlined to look for
> a global solution rather than tweaking each driver.
> 
> Given many drivers are supposed to work on legacy too, we know del_vqs
> includes a reset for many of them. So I think I see a better way to do
> this:
> 
> Add virtio_reset_device_and_del_vqs()
> 
> and convert all drivers to that.
> 
> When doing this, we also need to/can fix a related problem (and related
> to the hardening that Jason Wang was looking into):
> virtio_reset_device is inherently racy: vq interrupts could
> be in flight when we do reset. We need to prevent handlers from firing in
> the window between reset and freeing the irq, so we should first
> free irqs and only then start changing the state by e.g.
> device reset.
> 
> 
> Quite a lot of core work here. Jason are you still looking into
> hardening?
> 
Li Zetao, Jason, any updates. You guys looking into this?

> 
> > Li Zetao (4):
> >   9p: Fix probe failed when modprobe 9pnet_virtio
> >   virtio-mem: Fix probe failed when modprobe virtio_mem
> >   virtio-input: Fix probe failed when modprobe virtio_input
> >   virtio-blk: Fix probe failed when modprobe virtio_blk
> > 
> >  drivers/block/virtio_blk.c    | 1 +
> >  drivers/virtio/virtio_input.c | 1 +
> >  drivers/virtio/virtio_mem.c   | 1 +
> >  net/9p/trans_virtio.c         | 1 +
> >  4 files changed, 4 insertions(+)
> > 
> > -- 
> > 2.25.1