linux-kernel - [PATCH RFC 06/10] kfence, kasan: make KFENCE compatible with KASAN

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Message-Id: <20200907134055.2878499-7-elver@google.com>
Date:   Mon,  7 Sep 2020 15:40:51 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, glider@...gle.com, akpm@...ux-foundation.org,
        catalin.marinas@....com, cl@...ux.com, rientjes@...gle.com,
        iamjoonsoo.kim@....com, mark.rutland@....com, penberg@...nel.org
Cc:     hpa@...or.com, paulmck@...nel.org, andreyknvl@...gle.com,
        aryabinin@...tuozzo.com, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, dvyukov@...gle.com,
        edumazet@...gle.com, gregkh@...uxfoundation.org, mingo@...hat.com,
        jannh@...gle.com, corbet@....net, keescook@...omium.org,
        peterz@...radead.org, cai@....pw, tglx@...utronix.de,
        will@...nel.org, x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org
Subject: [PATCH RFC 06/10] kfence, kasan: make KFENCE compatible with KASAN

From: Alexander Potapenko <glider@...gle.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@...gle.com>
Signed-off-by: Marco Elver <elver@...gle.com>
Signed-off-by: Alexander Potapenko <glider@...gle.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 7ac91162edb0..b080e49e15d4 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,
-- 
2.28.0.526.ge36021eeef-goog