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Subject[PATCH v8 04/20] kasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_SW_TAGS
Date
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 to compile correctly with each of the
config options.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
arch/arm64/Kconfig | 1 +
include/linux/compiler-clang.h | 5 +-
include/linux/kasan.h | 16 +++++--
lib/Kconfig.kasan | 87 +++++++++++++++++++++++++++-------
mm/kasan/Makefile | 6 ++-
mm/kasan/generic.c | 2 +-
mm/kasan/kasan.h | 3 +-
mm/kasan/tags.c | 75 +++++++++++++++++++++++++++++
mm/slub.c | 2 +-
scripts/Makefile.kasan | 27 ++++++++++-
10 files changed, 194 insertions(+), 30 deletions(-)
create mode 100644 mm/kasan/tags.c

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1b1a0e95c751..287c32241b68 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -105,6 +105,7 @@ config ARM64
select HAVE_ARCH_HUGE_VMAP
select HAVE_ARCH_JUMP_LABEL
select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
+ select HAVE_ARCH_KASAN_SW_TAGS if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
select HAVE_ARCH_KGDB
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index b1ce500fe8b3..89ebe58259ba 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -17,11 +17,12 @@
#define KASAN_ABI_VERSION 5

/* emulate gcc's __SANITIZE_ADDRESS__ flag */
-#if __has_feature(address_sanitizer)
+#if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer)
#define __SANITIZE_ADDRESS__
#endif

-#define __no_sanitize_address __attribute__((no_sanitize("address")))
+#define __no_sanitize_address \
+ __attribute__((no_sanitize("address", "hwaddress")))

/*
* Not all versions of clang implement the the type-generic versions
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 3b019db87892..f0c96f08f2f1 100644
--- a/include/linux/kasan.h
+++ b/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 */
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index befb127507c0..181dfa7f4885 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -1,35 +1,86 @@
config HAVE_ARCH_KASAN
bool

+config HAVE_ARCH_KASAN_SW_TAGS
+ bool
+
if HAVE_ARCH_KASAN

config KASAN
- bool "KASan: runtime memory debugger"
+ bool "KASAN: runtime memory debugger"
+ 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 (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).

+if HAVE_ARCH_KASAN_SW_TAGS
+
+config KASAN_SW_TAGS
+ bool "Software tag-based mode"
+ 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).
+
+endif
+
+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
@@ -53,16 +104,16 @@ 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

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.
+ kernel debugging features like KASAN.

endif
diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index d643530b24aa..68ba1822f003 100644
--- a/mm/kasan/Makefile
+++ b/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
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 44ec228de0a2..b8de6d33c55c 100644
--- a/mm/kasan/generic.c
+++ b/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 <ryabinin.a.a@gmail.com>
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 659463800f10..19b950eaccff 100644
--- a/mm/kasan/kasan.h
+++ b/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);
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
new file mode 100644
index 000000000000..04194923c543
--- /dev/null
+++ b/mm/kasan/tags.c
@@ -0,0 +1,75 @@
+/*
+ * This file contains core tag-based KASAN code.
+ *
+ * Copyright (c) 2018 Google, Inc.
+ * Author: Andrey Konovalov <andreyknvl@google.com>
+ *
+ * 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);
diff --git a/mm/slub.c b/mm/slub.c
index b2172284d421..c4d5f4442ff1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2954,7 +2954,7 @@ 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);
diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 69552a39951d..5bf3a808a282 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -1,5 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
-ifdef CONFIG_KASAN
+ifdef CONFIG_KASAN_GENERIC
ifdef CONFIG_KASAN_INLINE
call_threshold := 10000
else
@@ -42,6 +42,29 @@ ifdef CONFIG_KASAN_EXTRA
CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
endif

-CFLAGS_KASAN_NOSANITIZE := -fno-builtin
+endif
+
+ifdef CONFIG_KASAN_SW_TAGS
+
+ifdef CONFIG_KASAN_INLINE
+ instrumentation_flags := -mllvm -hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET)
+else
+ instrumentation_flags := -mllvm -hwasan-instrument-with-calls=1
+endif

+CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
+ -mllvm -hwasan-instrument-stack=0 \
+ $(instrumentation_flags)
+
+ifeq ($(call cc-option, $(CFLAGS_KASAN) -Werror),)
+ ifneq ($(CONFIG_COMPILE_TEST),y)
+ $(warning Cannot use CONFIG_KASAN_SW_TAGS: \
+ -fsanitize=hwaddress is not supported by compiler)
+ endif
+endif
+
+endif
+
+ifdef CONFIG_KASAN
+CFLAGS_KASAN_NOSANITIZE := -fno-builtin
endif
--
2.19.0.397.gdd90340f6a-goog
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