From: Jason Wang <jasowang@redhat.com>
Date: Thu, 13 Dec 2018 02:53:37 +0000 (+0800)
Subject: vhost: make sure used idx is seen before log in vhost_add_used_n()
X-Git-Tag: v4.14.92~76
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=2510d91bdafe6ebe95864290866bb6c3e714b6e8;p=users%2Fjedix%2Flinux-maple.git

vhost: make sure used idx is seen before log in vhost_add_used_n()

[ Upstream commit 841df922417eb82c835e93d4b93eb6a68c99d599 ]

We miss a write barrier that guarantees used idx is updated and seen
before log. This will let userspace sync and copy used ring before
used idx is update. Fix this by adding a barrier before log_write().

Fixes: 8dd014adfea6f ("vhost-net: mergeable buffers support")
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index ffdd4e937d1d8..97518685ab58a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2231,6 +2231,8 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
 		return -EFAULT;
 	}
 	if (unlikely(vq->log_used)) {
+		/* Make sure used idx is seen before log. */
+		smp_wmb();
 		/* Log used index update. */
 		log_write(vq->log_base,
 			  vq->log_addr + offsetof(struct vring_used, idx),