From: "Michael S. Tsirkin" <mst@redhat.com>
To: Lee Jones <lee.jones@linaro.org>
Cc: Jason Wang <jasowang@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
kvm <kvm@vger.kernel.org>,
virtualization <virtualization@lists.linux-foundation.org>,
netdev <netdev@vger.kernel.org>,
stable@vger.kernel.org,
syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com
Subject: Re: [PATCH 1/1] vhost: Protect the virtqueue from being cleared whilst still in use
Date: Tue, 8 Mar 2022 06:06:47 -0500 [thread overview]
Message-ID: <20220308060542-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <YicO+aF4VhaBYNqK@google.com>
On Tue, Mar 08, 2022 at 08:08:25AM +0000, Lee Jones wrote:
> On Tue, 08 Mar 2022, Jason Wang wrote:
>
> > On Tue, Mar 8, 2022 at 3:18 AM Lee Jones <lee.jones@linaro.org> wrote:
> > >
> > > vhost_vsock_handle_tx_kick() already holds the mutex during its call
> > > to vhost_get_vq_desc(). All we have to do here is take the same lock
> > > during virtqueue clean-up and we mitigate the reported issues.
> > >
> > > Also WARN() as a precautionary measure. The purpose of this is to
> > > capture possible future race conditions which may pop up over time.
> > >
> > > Link: https://syzkaller.appspot.com/bug?extid=279432d30d825e63ba00
> > >
> > > Cc: <stable@vger.kernel.org>
> > > Reported-by: syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com
> > > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > > ---
> > > drivers/vhost/vhost.c | 10 ++++++++++
> > > 1 file changed, 10 insertions(+)
> > >
> > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > index 59edb5a1ffe28..ef7e371e3e649 100644
> > > --- a/drivers/vhost/vhost.c
> > > +++ b/drivers/vhost/vhost.c
> > > @@ -693,6 +693,15 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> > > int i;
> > >
> > > for (i = 0; i < dev->nvqs; ++i) {
> > > + /* No workers should run here by design. However, races have
> > > + * previously occurred where drivers have been unable to flush
> > > + * all work properly prior to clean-up. Without a successful
> > > + * flush the guest will malfunction, but avoiding host memory
> > > + * corruption in those cases does seem preferable.
> > > + */
> > > + WARN_ON(mutex_is_locked(&dev->vqs[i]->mutex));
> > > +
> >
> > I don't get how this can help, the mutex could be grabbed in the
> > middle of the above and below line.
>
> The worst that happens in this slim scenario is we miss a warning.
> The mutexes below will still function as expected and prevent possible
> memory corruption.
maybe. or maybe corruption already happened and this is the
fallout.
> > > + mutex_lock(&dev->vqs[i]->mutex);
> > > if (dev->vqs[i]->error_ctx)
> > > eventfd_ctx_put(dev->vqs[i]->error_ctx);
> > > if (dev->vqs[i]->kick)
> > > @@ -700,6 +709,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> > > if (dev->vqs[i]->call_ctx.ctx)
> > > eventfd_ctx_put(dev->vqs[i]->call_ctx.ctx);
> > > vhost_vq_reset(dev, dev->vqs[i]);
> > > + mutex_unlock(&dev->vqs[i]->mutex);
> > > }
> >
> > I'm not sure it's correct to assume some behaviour of a buggy device.
> > For the device mutex, we use that to protect more than just err/call
> > and vq.
>
> When I authored this, I did so as *the* fix. However, since the cause
> of today's crash has now been patched, this has become a belt and
> braces solution. Michael's addition of the WARN() also has the
> benefit of providing us with an early warning system for future
> breakages. Personally, I think it's kinda neat.
>
> --
> Lee Jones [李琼斯]
> Principal Technical Lead - Developer Services
> Linaro.org │ Open source software for Arm SoCs
> Follow Linaro: Facebook | Twitter | Blog
next prev parent reply other threads:[~2022-03-08 11:06 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-07 19:17 [PATCH 1/1] vhost: Protect the virtqueue from being cleared whilst still in use Lee Jones
2022-03-07 19:33 ` Greg KH
2022-03-07 22:39 ` Michael S. Tsirkin
2022-03-08 8:10 ` Lee Jones
2022-03-08 8:11 ` Lee Jones
2022-03-08 8:57 ` Greg KH
2022-03-08 9:15 ` Lee Jones
2022-03-08 9:57 ` Greg KH
2022-03-08 10:08 ` Lee Jones
2022-03-08 10:55 ` Michael S. Tsirkin
2022-03-08 11:45 ` Greg KH
2022-03-08 12:27 ` Michael S. Tsirkin
2022-03-08 13:17 ` Lee Jones
2022-03-08 17:17 ` Michael S. Tsirkin
2022-03-08 11:05 ` Michael S. Tsirkin
2022-03-09 18:52 ` Leon Romanovsky
2022-03-07 22:37 ` Michael S. Tsirkin
2022-03-08 8:01 ` Lee Jones
2022-03-08 11:07 ` Michael S. Tsirkin
2022-03-08 6:15 ` Jason Wang
2022-03-08 8:08 ` Lee Jones
2022-03-08 11:06 ` Michael S. Tsirkin [this message]
-- strict thread matches above, loose matches on Subject: below --
2022-03-14 8:43 Lee Jones
2022-03-14 8:56 ` Greg KH
2022-03-14 11:49 ` Michael S. Tsirkin
2022-03-14 12:47 ` Lee Jones
2022-03-02 7:54 Lee Jones
2022-03-02 9:34 ` Stefano Garzarella
2022-03-02 10:07 ` Lee Jones
2022-03-02 13:35 ` Michael S. Tsirkin
2022-03-02 14:11 ` Stefano Garzarella
2022-03-02 14:50 ` Michael S. Tsirkin
2022-03-02 15:36 ` Stefano Garzarella
2022-03-04 16:46 ` Michael S. Tsirkin
2022-03-02 13:30 ` Michael S. Tsirkin
2022-03-02 13:56 ` Lee Jones
2022-03-02 14:51 ` Michael S. Tsirkin
2022-03-02 14:57 ` Lee Jones
2022-03-02 16:28 ` Stefano Garzarella
2022-03-02 16:30 ` Michael S. Tsirkin
2022-03-02 16:49 ` Lee Jones
2022-03-02 17:10 ` Stefano Garzarella
2022-03-03 14:17 ` Lee Jones
2022-03-04 5:00 ` Michael S. Tsirkin
2022-03-04 15:22 ` Lee Jones
2022-03-04 16:48 ` Michael S. Tsirkin
2022-03-04 16:56 ` Lee Jones
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