netdev - [PATCH v2 1/2] vhost: Don't call access

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Date:   Tue, 29 Sep 2020 18:30:31 +0200
From:   Greg Kurz <groug@...d.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, qemu-devel@...gnu.org,
        Laurent Vivier <laurent@...ier.eu>,
        David Gibson <david@...son.dropbear.id.au>
Subject: [PATCH v2 1/2] vhost: Don't call access_ok() when using IOTLB

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@...hat.com
CC: stable@...r.kernel.org # 4.14+
Signed-off-by: Greg Kurz <groug@...d.org>
---
 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);