The patch titled Subject: mm: kmsan: fix poisoning of high-order non-compound pages has been added to the -mm mm-new branch. Its filename is mm-kmsan-fix-poisoning-of-high-order-non-compound-pages.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ryan Roberts ryan.roberts@arm.com Subject: mm: kmsan: fix poisoning of high-order non-compound pages Date: Sun, 4 Jan 2026 13:43:47 +0000

kmsan_free_page() is called by the page allocator's free_pages_prepare() during page freeing. Its job is to poison all the memory covered by the page. It can be called with an order-0 page, a compound high-order page or a non-compound high-order page. But page_size() only works for order-0 and compound pages. For a non-compound high-order page it will incorrectly return PAGE_SIZE.

The implication is that the tail pages of a high-order non-compound page do not get poisoned at free, so any invalid access while they are free could go unnoticed. It looks like the pages will be poisoned again at allocation time, so that would bookend the window.

Fix this by using the order parameter to calculate the size.

Link: https://lkml.kernel.org/r/20260104134348.3544298-1-ryan.roberts@arm.com Fixes: b073d7f8aee4 ("mm: kmsan: maintain KMSAN metadata for page operations") Signed-off-by: Ryan Roberts ryan.roberts@arm.com Cc: Alexander Potapenko glider@google.com Cc: Dmitriy Vyukov dvyukov@google.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Marco Elver elver@google.com Cc: Ryan Roberts ryan.roberts@arm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/kmsan/shadow.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/kmsan/shadow.c~mm-kmsan-fix-poisoning-of-high-order-non-compound-pages +++ a/mm/kmsan/shadow.c @@ -207,7 +207,7 @@ void kmsan_free_page(struct page *page, if (!kmsan_enabled || kmsan_in_runtime()) return; kmsan_enter_runtime(); - kmsan_internal_poison_memory(page_address(page), page_size(page), + kmsan_internal_poison_memory(page_address(page), PAGE_SIZE << order, GFP_KERNEL & ~(__GFP_RECLAIM), KMSAN_POISON_CHECK | KMSAN_POISON_FREE); kmsan_leave_runtime(); _

Patches currently in -mm which might be from ryan.roberts@arm.com are

mm-kmsan-fix-poisoning-of-high-order-non-compound-pages.patch