From cfcae0c99919fcf9b9d697a4856c8d13e10d408e Mon Sep 17 00:00:00 2001
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Thu, 6 Feb 2020 02:40:58 -0500
Subject: [PATCH] virtio_balloon: prevent pfn array overflow

commit 6e9826e77249355c09db6ba41cd3f84e89f4b614 upstream.

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@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index ef364fade45a..e20a3df08d8d 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -156,6 +156,8 @@ 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.
-- 
2.7.4