[PATCH v2 06/10] kfence, kasan: make KFENCE compatible with KASAN

From: Marco Elver <elver@google.com>
To: elver@google.com, akpm@linux-foundation.org, glider@google.com
Cc: hpa@zytor.com, paulmck@kernel.org, andreyknvl@google.com,
	aryabinin@virtuozzo.com, luto@kernel.org, bp@alien8.de,
	catalin.marinas@arm.com, cl@linux.com,
	dave.hansen@linux.intel.com, rientjes@google.com,
	dvyukov@google.com, edumazet@google.com,
	gregkh@linuxfoundation.org, mingo@redhat.com, jannh@google.com,
	Jonathan.Cameron@huawei.com, corbet@lwn.net,
	iamjoonsoo.kim@lge.com, keescook@chromium.org,
	mark.rutland@arm.com, penberg@kernel.org, peterz@infradead.org,
	cai@lca.pw, tglx@linutronix.de, vbabka@suse.cz, will@kernel.org,
	x86@kernel.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
	linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org
Subject: [PATCH v2 06/10] kfence, kasan: make KFENCE compatible with KASAN
Date: Tue, 15 Sep 2020 15:20:42 +0200	[thread overview]
Message-ID: <20200915132046.3332537-7-elver@google.com> (raw)
In-Reply-To: <20200915132046.3332537-1-elver@google.com>

From: Alexander Potapenko <glider@google.com>

We make KFENCE compatible with KASAN for testing KFENCE itself. In
particular, KASAN helps to catch any potential corruptions to KFENCE
state, or other corruptions that may be a result of freepointer
corruptions in the main allocators.

To indicate that the combination of the two is generally discouraged,
CONFIG_EXPERT=y should be set. It also gives us the nice property that
KFENCE will be build-tested by allyesconfig builds.

Co-developed-by: Marco Elver <elver@google.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
---
 lib/Kconfig.kfence | 2 +-
 mm/kasan/common.c  | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence
index 6a90fef41832..872bcbdd8cc4 100644
--- a/lib/Kconfig.kfence
+++ b/lib/Kconfig.kfence
@@ -10,7 +10,7 @@ config HAVE_ARCH_KFENCE_STATIC_POOL
 
 menuconfig KFENCE
 	bool "KFENCE: low-overhead sampling-based memory safety error detector"
-	depends on HAVE_ARCH_KFENCE && !KASAN && (SLAB || SLUB)
+	depends on HAVE_ARCH_KFENCE && (!KASAN || EXPERT) && (SLAB || SLUB)
 	depends on JUMP_LABEL # To ensure performance, require jump labels
 	select STACKTRACE
 	help
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 950fd372a07e..f5c49f0fdeff 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -18,6 +18,7 @@
 #include <linux/init.h>
 #include <linux/kasan.h>
 #include <linux/kernel.h>
+#include <linux/kfence.h>
 #include <linux/kmemleak.h>
 #include <linux/linkage.h>
 #include <linux/memblock.h>
@@ -396,6 +397,9 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
 	tagged_object = object;
 	object = reset_tag(object);
 
+	if (is_kfence_address(object))
+		return false;
+
 	if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
 	    object)) {
 		kasan_report_invalid_free(tagged_object, ip);
@@ -444,6 +448,9 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
 	if (unlikely(object == NULL))
 		return NULL;
 
+	if (is_kfence_address(object))
+		return (void *)object;
+
 	redzone_start = round_up((unsigned long)(object + size),
 				KASAN_SHADOW_SCALE_SIZE);
 	redzone_end = round_up((unsigned long)object + cache->object_size,
-- 
2.28.0.618.gf4bc123cb7-goog

