Linux Virtualization - Feb 2020 - [PATCH] virtio_balloon: prevent pfn array overflow

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>
---
 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 8e400ece9273..2457c54b6185 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -158,6 +158,8 @@ 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.
-- 
MST

On 06.02.20 08:47, Michael S. Tsirkin wrote:
> 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>
> ---
>  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 8e400ece9273..2457c54b6185 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -158,6 +158,8 @@ 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.
> 
Reviewed-by: David Hildenbrand <david at redhat.com>

-- 
Thanks,

David / dhildenb

On 2020/2/6 ??3:47, Michael S. Tsirkin wrote:
> 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>
> ---
>   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 8e400ece9273..2457c54b6185 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -158,6 +158,8 @@ 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.

Acked-by: Jason Wang <jasowang at redhat.com>