FAILED: patch "[PATCH] mm: kmsan: fix poisoning of high-order non-compound pages" failed to apply to 6.12-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 4795d205d78690a46b60164f44b8bb7b3e800865
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026012026-varying-grappling-04b4@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4795d205d78690a46b60164f44b8bb7b3e800865 Mon Sep 17 00:00:00 2001
From: Ryan Roberts <ryan.roberts@arm.com>
Date: Sun, 4 Jan 2026 13:43:47 +0000
Subject: [PATCH] mm: kmsan: fix poisoning of high-order non-compound pages

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>
Reviewed-by: Alexander Potapenko <glider@google.com>
Tested-by: 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>

diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
index e7f554a31bb4..9e1c5f2b7a41 100644
--- a/mm/kmsan/shadow.c
+++ b/mm/kmsan/shadow.c
@@ -207,7 +207,7 @@ void kmsan_free_page(struct page *page, unsigned int order)
 	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();