+ mm-kmsan-fix-poisoning-of-high-order-non-compound-pages.patch added to mm-new branch

+ mm-kmsan-fix-poisoning-of-high-order-non-compound-pages.patch added to mm-new branch

[Andrew Morton]

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

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

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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