+ kfence-clear-the-pool-pointer-before-freeing-pages.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: kfence: clear the pool pointer before freeing pages
has been added to the -mm mm-new branch.  Its filename is
     kfence-clear-the-pool-pointer-before-freeing-pages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kfence-clear-the-pool-pointer-before-freeing-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.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Jackie Liu <liuyun01@kylinos.cn>
Subject: kfence: clear the pool pointer before freeing pages
Date: Thu, 29 Oct 2026 10:57:42 +0800

Late initialization frees a failed pool before clearing __kfence_pool.
Slab allocations can reuse those pages in between and be mistaken for
KFENCE objects by is_kfence_address(), even though KFENCE is not enabled.

Clear __kfence_pool before freeing the pages, and use the saved address
for cleanup.

Link: https://lore.kernel.org/2fab8aaa82ab2004e706fd7ec8dac20427976457.1793242457.git.liuyun01@kylinos.cn
Fixes: b33f778bba5e ("kfence: alloc kfence_pool after system startup")
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Paul Walmsley <pjw@kernel.org>
Cc: AlexandreGhiti <alex@ghiti.fr>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
---

 mm/kfence/core.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/kfence/core.c~kfence-clear-the-pool-pointer-before-freeing-pages
+++ a/mm/kfence/core.c
@@ -1052,16 +1052,17 @@ static int kfence_init_late(void)
 	free_contig_range(page_to_pfn(virt_to_page((void *)kfence_metadata_init)),
 			  nr_pages_meta);
 free_pool:
+	WRITE_ONCE(__kfence_pool, NULL);
 	free_contig_range(page_to_pfn(virt_to_page((void *)addr)),
 			  free_size / PAGE_SIZE);
 #else
 	free_pages_exact((void *)kfence_metadata_init, KFENCE_METADATA_SIZE);
 free_pool:
+	WRITE_ONCE(__kfence_pool, NULL);
 	free_pages_exact((void *)addr, free_size);
 #endif
 
 	kfence_metadata_init = NULL;
-	__kfence_pool = NULL;
 	return err;
 }
 
_

Patches currently in -mm which might be from liuyun01@kylinos.cn are

kfence-fix-pool-cleanup-on-metadata-allocation-failure.patch
kfence-clear-the-pool-pointer-before-freeing-pages.patch
riscv-keep-booting-if-kfence-pool-reservation-fails.patch