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virtio-balloon: Fix QEMU crashes on pagesize > BALLOON_PAGE_SIZE

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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-stable@nongnu.org #v4.0.0
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190722134108.22151-3-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
David Hildenbrand 2019-07-22 15:41:04 +02:00 committed by Michael S. Tsirkin
parent ffa207d082
commit 483f13524b
1 changed files with 4 additions and 6 deletions
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10
hw/virtio/virtio-balloon.c
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@ -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);