On Tue, Apr 10, 2018 at 04:22:35PM +0300, Michael S. Tsirkin wrote:
> On Tue, Apr 10, 2018 at 01:26:29PM +0800, Stefan Hajnoczi wrote:
> > Commit d65026c6c62e7d9616c8ceb5a53b68bcdc050525 ("vhost: validate log
> > when IOTLB is enabled") introduced a regression. The logic was
> > originally:
> >
> > if (vq->iotlb)
> > return 1;
> > return A && B;
> >
> > After the patch the short-circuit logic for A was inverted:
> >
> > if (A || vq->iotlb)
> > return A;
> > return B;
> >
> > This patch fixes the regression by rewriting the checks in the obvious
> > way, no longer returning A when vq->iotlb is non-NULL (which is hard to
> > understand).
> >
> > Reported-by: syzbot+65a84dde0214b0387ccd@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Cc: Jason Wang <jasowang@xxxxxxxxxx>
> > Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
>
> This patch only makes sense after patch 2/2 is applied.
> Otherwise the logic seems reversed below.
>
> Can you pls squash these two?
Oh, in fact the patch is ok. This just goes to show
that patch 2/2 is useful. But squashing is not required.
Sorry about the noise.
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Fixes: d65026c6c ("vhost: validate log when IOTLB is enabled")
probably stable material since patch it fixes was queued to stable?
> > ---
> > drivers/vhost/vhost.c | 8 +++++---
> > 1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 5320039671b7..93fd0c75b0d8 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -1244,10 +1244,12 @@ static int vq_log_access_ok(struct vhost_virtqueue *vq,
> > /* Caller should have vq mutex and device mutex */
> > int vhost_vq_access_ok(struct vhost_virtqueue *vq)
> > {
> > - int ret = vq_log_access_ok(vq, vq->log_base);
> > + if (!vq_log_access_ok(vq, vq->log_base))
> > + return 0;
> >
> > - if (ret || vq->iotlb)
> > - return ret;
> > + /* Access validation occurs at prefetch time with IOTLB */
> > + if (vq->iotlb)
> > + return 1;
> >
> > return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
> > }
> > --
> > 2.14.3
