[PATCH net] vhost: Fix Spectre V1 vulnerability

[Jason Wang]

The idx in vhost_vring_ioctl() was controlled by userspace, hence a
potential exploitation of the Spectre variant 1 vulnerability.

Fixing this by sanitizing idx before using it to index d->vqs.

Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/vhost/vhost.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index f52008bb8df7..3a5f81a66d34 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -30,6 +30,7 @@
 #include <linux/sched/mm.h>
 #include <linux/sched/signal.h>
 #include <linux/interval_tree_generic.h>
+#include <linux/nospec.h>
 
 #include "vhost.h"
 
@@ -1387,6 +1388,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
 	if (idx >= d->nvqs)
 		return -ENOBUFS;
 
+	idx = array_index_nospec(idx, d->nvqs);
 	vq = d->vqs[idx];
 
 	mutex_lock(&vq->mutex);
-- 
2.17.1