kasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_SW_TAGS

This commit splits the current CONFIG_KASAN config option into two:
1. CONFIG_KASAN_GENERIC, that enables the generic KASAN mode (the one
   that exists now);
2. CONFIG_KASAN_SW_TAGS, that enables the software tag-based KASAN mode.

The name CONFIG_KASAN_SW_TAGS is chosen as in the future we will have
another hardware tag-based KASAN mode, that will rely on hardware memory
tagging support in arm64.

With CONFIG_KASAN_SW_TAGS enabled, compiler options are changed to
instrument kernel files with -fsantize=kernel-hwaddress (except the ones
for which KASAN_SANITIZE := n is set).

Both CONFIG_KASAN_GENERIC and CONFIG_KASAN_SW_TAGS support both
CONFIG_KASAN_INLINE and CONFIG_KASAN_OUTLINE instrumentation modes.

This commit also adds empty placeholder (for now) implementation of
tag-based KASAN specific hooks inserted by the compiler and adjusts
common hooks implementation.

While this commit adds the CONFIG_KASAN_SW_TAGS config option, this option
is not selectable, as it depends on HAVE_ARCH_KASAN_SW_TAGS, which we will
enable once all the infrastracture code has been added.

Link: http://lkml.kernel.org/r/b2550106eb8a68b10fefbabce820910b115aa853.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <[email protected]>
Reviewed-by: Andrey Ryabinin <[email protected]>
Reviewed-by: Dmitry Vyukov <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/compiler-clang.h

@@ -16,9 +16,13 @@
 /* all clang versions usable with the kernel support KASAN ABI version 5 */
 #define KASAN_ABI_VERSION 5
 
+#if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer)
 /* emulate gcc's __SANITIZE_ADDRESS__ flag */
-#if __has_feature(address_sanitizer)
 #define __SANITIZE_ADDRESS__
+#define __no_sanitize_address \
+		__attribute__((no_sanitize("address", "hwaddress")))
+#else
+#define __no_sanitize_address
 #endif
 
 /*

include/linux/compiler-gcc.h

@@ -143,6 +143,12 @@
 #define KASAN_ABI_VERSION 3
 #endif
 
+#if __has_attribute(__no_sanitize_address__)
+#define __no_sanitize_address __attribute__((no_sanitize_address))
+#else
+#define __no_sanitize_address
+#endif
+
 #if GCC_VERSION >= 50100
 #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
 #endif

include/linux/compiler_attributes.h

@@ -199,19 +199,6 @@
  */
 #define __noreturn                      __attribute__((__noreturn__))
 
-/*
- * Optional: only supported since gcc >= 4.8
- * Optional: not supported by icc
- *
- *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fsanitize_005faddress-function-attribute
- * clang: https://clang.llvm.org/docs/AttributeReference.html#no-sanitize-address-no-address-safety-analysis
- */
-#if __has_attribute(__no_sanitize_address__)
-# define __no_sanitize_address          __attribute__((__no_sanitize_address__))
-#else
-# define __no_sanitize_address
-#endif
-
 /*
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute
  * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute

include/linux/kasan.h

@@ -45,8 +45,6 @@ void kasan_free_pages(struct page *page, unsigned int order);
 
 void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 			slab_flags_t *flags);
-void kasan_cache_shrink(struct kmem_cache *cache);
-void kasan_cache_shutdown(struct kmem_cache *cache);
 
 void kasan_poison_slab(struct page *page);
 void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
@@ -97,8 +95,6 @@ static inline void kasan_free_pages(struct page *page, unsigned int order) {}
 static inline void kasan_cache_create(struct kmem_cache *cache,
 				      unsigned int *size,
 				      slab_flags_t *flags) {}
-static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
-static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
 
 static inline void kasan_poison_slab(struct page *page) {}
 static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
@@ -155,4 +151,16 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
 
 #endif /* CONFIG_KASAN */
 
+#ifdef CONFIG_KASAN_GENERIC
+
+void kasan_cache_shrink(struct kmem_cache *cache);
+void kasan_cache_shutdown(struct kmem_cache *cache);
+
+#else /* CONFIG_KASAN_GENERIC */
+
+static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
+static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
+
+#endif /* CONFIG_KASAN_GENERIC */
+
 #endif /* LINUX_KASAN_H */

lib/Kconfig.kasan

@@ -1,36 +1,92 @@
+# This config refers to the generic KASAN mode.
 config HAVE_ARCH_KASAN
 	bool
 
-if HAVE_ARCH_KASAN
+config HAVE_ARCH_KASAN_SW_TAGS
+	bool
+
+config CC_HAS_KASAN_GENERIC
+	def_bool $(cc-option, -fsanitize=kernel-address)
+
+config CC_HAS_KASAN_SW_TAGS
+	def_bool $(cc-option, -fsanitize=kernel-hwaddress)
 
 config KASAN
-	bool "KASan: runtime memory debugger"
+	bool "KASAN: runtime memory debugger"
+	depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \
+		   (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)
+	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
+	help
+	  Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
+	  designed to find out-of-bounds accesses and use-after-free bugs.
+	  See Documentation/dev-tools/kasan.rst for details.
+
+choice
+	prompt "KASAN mode"
+	depends on KASAN
+	default KASAN_GENERIC
+	help
+	  KASAN has two modes: generic KASAN (similar to userspace ASan,
+	  x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and
+	  software tag-based KASAN (a version based on software memory
+	  tagging, arm64 only, similar to userspace HWASan, enabled with
+	  CONFIG_KASAN_SW_TAGS).
+	  Both generic and tag-based KASAN are strictly debugging features.
+
+config KASAN_GENERIC
+	bool "Generic mode"
+	depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
 	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
 	select SLUB_DEBUG if SLUB
 	select CONSTRUCTORS
 	select STACKDEPOT
 	help
-	  Enables kernel address sanitizer - runtime memory debugger,
-	  designed to find out-of-bounds accesses and use-after-free bugs.
-	  This is strictly a debugging feature and it requires a gcc version
-	  of 4.9.2 or later. Detection of out of bounds accesses to stack or
-	  global variables requires gcc 5.0 or later.
-	  This feature consumes about 1/8 of available memory and brings about
-	  ~x3 performance slowdown.
+	  Enables generic KASAN mode.
+	  Supported in both GCC and Clang. With GCC it requires version 4.9.2
+	  or later for basic support and version 5.0 or later for detection of
+	  out-of-bounds accesses for stack and global variables and for inline
+	  instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires
+	  version 3.7.0 or later and it doesn't support detection of
+	  out-of-bounds accesses for global variables yet.
+	  This mode consumes about 1/8th of available memory at kernel start
+	  and introduces an overhead of ~x1.5 for the rest of the allocations.
+	  The performance slowdown is ~x3.
 	  For better error detection enable CONFIG_STACKTRACE.
-	  Currently CONFIG_KASAN doesn't work with CONFIG_DEBUG_SLAB
+	  Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
 	  (the resulting kernel does not boot).
 
+config KASAN_SW_TAGS
+	bool "Software tag-based mode"
+	depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
+	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
+	select SLUB_DEBUG if SLUB
+	select CONSTRUCTORS
+	select STACKDEPOT
+	help
+	  Enables software tag-based KASAN mode.
+	  This mode requires Top Byte Ignore support by the CPU and therefore
+	  is only supported for arm64.
+	  This mode requires Clang version 7.0.0 or later.
+	  This mode consumes about 1/16th of available memory at kernel start
+	  and introduces an overhead of ~20% for the rest of the allocations.
+	  This mode may potentially introduce problems relating to pointer
+	  casting and comparison, as it embeds tags into the top byte of each
+	  pointer.
+	  For better error detection enable CONFIG_STACKTRACE.
+	  Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB
+	  (the resulting kernel does not boot).
+
+endchoice
+
 config KASAN_EXTRA
-	bool "KAsan: extra checks"
-	depends on KASAN && DEBUG_KERNEL && !COMPILE_TEST
+	bool "KASAN: extra checks"
+	depends on KASAN_GENERIC && DEBUG_KERNEL && !COMPILE_TEST
 	help
-	  This enables further checks in the kernel address sanitizer, for now
-	  it only includes the address-use-after-scope check that can lead
-	  to excessive kernel stack usage, frame size warnings and longer
+	  This enables further checks in generic KASAN, for now it only
+	  includes the address-use-after-scope check that can lead to
+	  excessive kernel stack usage, frame size warnings and longer
 	  compile time.
-	  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 has more
-
+	  See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715
 
 choice
 	prompt "Instrumentation type"
@@ -53,7 +109,7 @@ config KASAN_INLINE
 	  memory accesses. This is faster than outline (in some workloads
 	  it gives about x2 boost over outline instrumentation), but
 	  make kernel's .text size much bigger.
-	  This requires a gcc version of 5.0 or later.
+	  For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
 
 endchoice
 
@@ -67,11 +123,9 @@ config KASAN_S390_4_LEVEL_PAGING
 	  4-level paging instead.
 
 config TEST_KASAN
-	tristate "Module for testing kasan for bug detection"
+	tristate "Module for testing KASAN for bug detection"
 	depends on m && KASAN
 	help
 	  This is a test module doing various nasty things like
 	  out of bounds accesses, use after free. It is useful for testing
-	  kernel debugging features like kernel address sanitizer.
-
-endif
+	  kernel debugging features like KASAN.

mm/kasan/Makefile

@@ -2,6 +2,7 @@
 KASAN_SANITIZE := n
 UBSAN_SANITIZE_common.o := n
 UBSAN_SANITIZE_generic.o := n
+UBSAN_SANITIZE_tags.o := n
 KCOV_INSTRUMENT := n
 
 CFLAGS_REMOVE_generic.o = -pg
@@ -10,5 +11,8 @@ CFLAGS_REMOVE_generic.o = -pg
 
 CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 CFLAGS_generic.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
+CFLAGS_tags.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
-obj-y := common.o generic.o report.o init.o quarantine.o
+obj-$(CONFIG_KASAN) := common.o init.o report.o
+obj-$(CONFIG_KASAN_GENERIC) += generic.o quarantine.o
+obj-$(CONFIG_KASAN_SW_TAGS) += tags.o

mm/kasan/generic.c

@@ -1,5 +1,5 @@
 /*
- * This file contains core KASAN code.
+ * This file contains core generic KASAN code.
  *
  * Copyright (c) 2014 Samsung Electronics Co., Ltd.
  * Author: Andrey Ryabinin <[email protected]>

mm/kasan/kasan.h

@@ -114,7 +114,8 @@ void kasan_report(unsigned long addr, size_t size,
 		bool is_write, unsigned long ip);
 void kasan_report_invalid_free(void *object, unsigned long ip);
 
-#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
+#if defined(CONFIG_KASAN_GENERIC) && \
+	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
 void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
 void quarantine_reduce(void);
 void quarantine_remove_cache(struct kmem_cache *cache);

mm/kasan/tags.c

@@ -0,0 +1,75 @@
+/*
+ * This file contains core tag-based KASAN code.
+ *
+ * Copyright (c) 2018 Google, Inc.
+ * Author: Andrey Konovalov <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#define DISABLE_BRANCH_PROFILING
+
+#include <linux/export.h>
+#include <linux/interrupt.h>
+#include <linux/init.h>
+#include <linux/kasan.h>
+#include <linux/kernel.h>
+#include <linux/kmemleak.h>
+#include <linux/linkage.h>
+#include <linux/memblock.h>
+#include <linux/memory.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <linux/slab.h>
+#include <linux/stacktrace.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/vmalloc.h>
+#include <linux/bug.h>
+
+#include "kasan.h"
+#include "../slab.h"
+
+void check_memory_region(unsigned long addr, size_t size, bool write,
+				unsigned long ret_ip)
+{
+}
+
+#define DEFINE_HWASAN_LOAD_STORE(size)					\
+	void __hwasan_load##size##_noabort(unsigned long addr)		\
+	{								\
+	}								\
+	EXPORT_SYMBOL(__hwasan_load##size##_noabort);			\
+	void __hwasan_store##size##_noabort(unsigned long addr)		\
+	{								\
+	}								\
+	EXPORT_SYMBOL(__hwasan_store##size##_noabort)
+
+DEFINE_HWASAN_LOAD_STORE(1);
+DEFINE_HWASAN_LOAD_STORE(2);
+DEFINE_HWASAN_LOAD_STORE(4);
+DEFINE_HWASAN_LOAD_STORE(8);
+DEFINE_HWASAN_LOAD_STORE(16);
+
+void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
+{
+}
+EXPORT_SYMBOL(__hwasan_loadN_noabort);
+
+void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
+{
+}
+EXPORT_SYMBOL(__hwasan_storeN_noabort);
+
+void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
+{
+}
+EXPORT_SYMBOL(__hwasan_tag_memory);

mm/slub.c

@@ -2992,7 +2992,7 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
 		do_slab_free(s, page, head, tail, cnt, addr);
 }
 
-#ifdef CONFIG_KASAN
+#ifdef CONFIG_KASAN_GENERIC
 void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr)
 {
 	do_slab_free(cache, virt_to_head_page(x), x, NULL, 1, addr);