[PATCH v1] mm/kfence: disable KFENCE upon KASAN HW tags enablement

[Alexander Potapenko]

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.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Ernesto Martinez Garcia <ernesto.martinezgarcia@xxxxxxxxx>
Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <kees@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Suggested-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
---
 mm/kfence/core.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 4f79ec7207525..71f87072baf9b 100644
--- 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>
@@ -911,6 +912,20 @@ void __init kfence_alloc_pool_and_metadata(void)
 	if (!kfence_sample_interval)
 		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.
-- 
2.53.0.273.g2a3d683680-goog