Re: [PATCH v2 1/2] vhost: Don't call access_ok() when using IOTLB

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On 2020/9/30 上午12:30, Greg Kurz wrote:
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>
---
  drivers/vhost/vhost.c |    9 +++++----
  1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b45519ca66a7..c3b49975dc28 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1290,6 +1290,11 @@ static bool vq_access_ok(struct vhost_virtqueue *vq, unsigned int num,
  			 vring_used_t __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));
@@ -1383,10 +1388,6 @@ bool vhost_vq_access_ok(struct vhost_virtqueue *vq)
  	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);


Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

Thanks





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