Virtualization - Feb 2020 - [PATCH AUTOSEL 4.19 251/252] virtio_balloon: prevent pfn array overflow

From: "Michael S. Tsirkin" <mst at redhat.com>

[ Upstream commit 6e9826e77249355c09db6ba41cd3f84e89f4b614 ]

Make sure, at build time, that pfn array is big enough to hold a single
page.  It happens to be true since the PAGE_SHIFT value at the moment is
20, which is 1M - exactly 256 4K balloon pages.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Reviewed-by: David Hildenbrand <david at redhat.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/virtio/virtio_balloon.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 14ac36ca8fbd3..1afcbef397ab7 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -126,6 +126,8 @@ static void set_page_pfns(struct virtio_balloon *vb,
 {
 	unsigned int i;
 
+	BUILD_BUG_ON(VIRTIO_BALLOON_PAGES_PER_PAGE >
VIRTIO_BALLOON_ARRAY_PFNS_MAX);
+
 	/*
 	 * Set balloon pfns pointing at this page.
 	 * Note that the first pfn points at start of the page.
-- 
2.20.1