[PATCH 5.4 11/85] vhost: Dont call access_ok() when using IOTLB

From: Greg Kroah-Hartman
Date: Mon Oct 12 2020 - 09:41:51 EST


From: Greg Kurz <groug@xxxxxxxx>

commit 0210a8db2aeca393fb3067e234967877e3146266 upstream.

When the IOTLB device is enabled, the vring addresses we get
from userspace are GIOVAs. It is thus wrong to pass them down
to access_ok() which only takes HVAs.

Access validation is done at prefetch time with IOTLB. Teach
vq_access_ok() about that by moving the (vq->iotlb) check
from vhost_vq_access_ok() to vq_access_ok(). This prevents
vhost_vring_set_addr() to fail when verifying the accesses.
No behavior change for vhost_vq_access_ok().

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1883084
Fixes: 6b1e6cc7855b ("vhost: new device IOTLB API")
Cc: jasowang@xxxxxxxxxx
CC: stable@xxxxxxxxxxxxxxx # 4.14+
Signed-off-by: Greg Kurz <groug@xxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Link: https://lore.kernel.org/r/160171931213.284610.2052489816407219136.stgit@xxxxxxxxx
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/vhost/vhost.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1299,6 +1299,11 @@ static bool vq_access_ok(struct vhost_vi
struct vring_used __user *used)

{
+ /* If an IOTLB device is present, the vring addresses are
+ * GIOVAs. Access validation occurs at prefetch time. */
+ if (vq->iotlb)
+ return true;
+
return access_ok(desc, vhost_get_desc_size(vq, num)) &&
access_ok(avail, vhost_get_avail_size(vq, num)) &&
access_ok(used, vhost_get_used_size(vq, num));
@@ -1394,10 +1399,6 @@ bool vhost_vq_access_ok(struct vhost_vir
if (!vq_log_access_ok(vq, vq->log_base))
return false;

- /* Access validation occurs at prefetch time with IOTLB */
- if (vq->iotlb)
- return true;
-
return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
}
EXPORT_SYMBOL_GPL(vhost_vq_access_ok);