[PATCH 6.12 120/460] mm/kfence: disable KFENCE upon KASAN HW tags enablement

Greg Kroah-Hartman
2026-03-23T14:18:10Z

6.12-stable review patch. If anyone has any objections, please let me know.

------------------

From: Alexander Potapenko <glider@google.com>

commit 09833d99db36d74456a4d13eb29c32d56ff8f2b6 upstream.

KFENCE does not currently support KASAN hardware tags. As a result, the
two features are incompatible when enabled simultaneously.

Given that MTE provides deterministic protection and KFENCE is a
sampling-based debugging tool, prioritize the stronger hardware
protections. Disable KFENCE initialization and free the pre-allocated
pool if KASAN hardware tags are detected to ensure the system maintains
the security guarantees provided by MTE.

Link: https://lkml.kernel.org/r/20260213095410.1862978-1-glider@google.com
Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: Alexander Potapenko <glider@google.com>
Suggested-by: Marco Elver <elver@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ernesto Martinez Garcia <ernesto.martinezgarcia@tugraz.at>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Kees Cook <kees@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/kfence/core.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -13,6 +13,7 @@
#include <linux/hash.h>
#include <linux/irq_work.h>
#include <linux/jhash.h>
+#include <linux/kasan-enabled.h>
#include <linux/kcsan-checks.h>
#include <linux/kfence.h>
#include <linux/kmemleak.h>
@@ -881,6 +882,20 @@ void __init kfence_alloc_pool_and_metada
return;

/*
+ * If KASAN hardware tags are enabled, disable KFENCE, because it
+ * does not support MTE yet.
+ */
+ if (kasan_hw_tags_enabled()) {
+ pr_info("disabled as KASAN HW tags are enabled\n");
+ if (__kfence_pool) {
+ memblock_free(__kfence_pool, KFENCE_POOL_SIZE);
+ __kfence_pool = NULL;
+ }
+ kfence_sample_interval = 0;
+ return;
+ }
+
+ /*
* If the pool has already been initialized by arch, there is no need to
* re-allocate the memory pool.
*/