We are using the wrong functions to set/clear bits, effectively touching
multiple bits, writing out of range of the bitmap, resulting in memory
corruptions. We have to use set_bit()/clear_bit() instead.
Can easily be reproduced by starting a qemu guest on hugetlbfs memory,
inflating the balloon. QEMU crashes. This never could have worked
properly - especially, also pages would have been discarded when the
first sub-page would be inflated (the whole bitmap would be set).
While testing I realized, that on hugetlbfs it is pretty much impossible
to discard a page - the guest just frees the 4k sub-pages in random order
most of the time. I was only able to discard a hugepage a handful of
times - so I hope that now works correctly.
Fixes: ed48c59875b6 ("virtio-balloon: Safely handle BALLOON_PAGE_SIZE <
host page size")
Fixes: b27b32391404 ("virtio-balloon: Fix possible guest memory corruption
with inflates & deflates")
Cc: qemu-sta...@nongnu.org #v4.0.0
Cc: Stefan Hajnoczi <stefa...@redhat.com>
Cc: David Gibson <da...@gibson.dropbear.id.au>
Cc: Michael S. Tsirkin <m...@redhat.com>
Cc: Igor Mammedov <imamm...@redhat.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
hw/virtio/virtio-balloon.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index e85d1c0d5c..669067d661 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -94,9 +94,8 @@ static void balloon_inflate_page(VirtIOBalloon *balloon,
balloon->pbp->base = host_page_base;
}
- bitmap_set(balloon->pbp->bitmap,
- (ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE,
- subpages);
+ set_bit((ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE,
+ balloon->pbp->bitmap);
if (bitmap_full(balloon->pbp->bitmap, subpages)) {
/* We've accumulated a full host page, we can actually discard
@@ -140,9 +139,8 @@ static void balloon_deflate_page(VirtIOBalloon *balloon,
* for a guest to do this in practice, but handle it anyway,
* since getting it wrong could mean discarding memory the
* guest is still using. */
- bitmap_clear(balloon->pbp->bitmap,
- (ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE,
- subpages);
+ clear_bit((ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE,
+ balloon->pbp->bitmap);
if (bitmap_empty(balloon->pbp->bitmap, subpages)) {
g_free(balloon->pbp);
--
2.21.0
