khwasan: kernel hardware assisted address sanitizer

RFC PATCH Superseded Andrey Konovalov 2 participants 18 messages Apr 20, 2018 – May 28, 2018

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Andrey Konovalov

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2018-04-20 14:38 UTC #0 lore raw

v3 cover khwasan: kernel hardware assisted address sanitizer

Hi! This is the 3rd RFC version of the patchset.

This patchset adds a new mode to KASAN [1], which is called KHWASAN (Kernel HardWare assisted Address SANitizer). There's still some work to do and there are a few TODOs in the code, so I'm publishing this as an RFC to collect some initial feedback.

The plan is to implement HWASan [2] for the kernel with the incentive, that it's going to have comparable to KASAN performance, but in the same time consume much less memory, trading that off for somewhat imprecise bug detection and being supported only for arm64.

The overall idea of the approach used by KHWASAN is the following:

1. By using the Top Byte Ignore arm64 CPU feature, we can store pointer tags in the top byte of each kernel pointer.

2. Using shadow memory, we can store memory tags for each chunk of kernel memory.

3. On each memory allocation, we can generate a random tag, embed it into the returned pointer and set the memory tags that correspond to this chunk of memory to the same value.

4. By using compiler instrumentation, before each memory access we can add a check that the pointer tag matches the tag of the memory that is being accessed.

5. On a tag mismatch we report an error.

[1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html

[2] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

====== Technical details

KHWASAN is implemented in a very similar way to KASAN. This patchset essentially does the following:

1. TCR_TBI1 is set to enable Top Byte Ignore.

2. Shadow memory is used (with a different scale, 1:16, so each shadow byte corresponds to 16 bytes of kernel memory) to store memory tags.

3. All slab objects are aligned to shadow scale, which is 16 bytes.

4. All pointers returned from the slab allocator are tagged with a random tag and the corresponding shadow memory is poisoned with the same value.

5. Compiler instrumentation is used to insert tag checks. Either by calling callbacks or by inlining them (CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE flags are reused).

6. When a tag mismatch is detected in callback instrumentation mode KHWASAN simply prints a bug report. In case of inline instrumentation, clang inserts a brk instruction, and KHWASAN has it's own brk handler, which reports the bug.

7. The memory in between slab objects is marked with a reserved tag, and acts as a redzone.

8. When a slab object is freed it's marked with a reserved tag.

Bug detection is imprecise for two reasons:

1. We won't catch some small out-of-bounds accesses, that fall into the same shadow cell, as the last byte of a slab object.

2. We only have 1 byte to store tags, which means we have a 1/256 probability of a tag match for an incorrect access (actually even slightly less due to reserved tag values).

====== Benchmarks

The following numbers were collected on Odroid C2 board. Both KASAN and KHWASAN were used in inline instrumentation mode. These are the numbers I got with the current prototype and they might change.

Boot time [1]:
* ~4.5 sec for clean kernel
* ~5.0 sec for KASAN
* ~5.1 sec for KHWASAN

Slab memory usage after boot [2]:
* ~32 kb for clean kernel
* ~95 kb + 1/8th shadow ~= 107 kb for KASAN
* ~38 kb + 1/16th shadow ~= 40 kb for KHWASAN

Network performance [3]:
* 11.9 Gbits/sec for clean kernel
* 3.08 Gbits/sec for KASAN
* 3.02 Gbits/sec for KHWASAN

Note, that KHWASAN (compared to KASAN) doesn't require quarantine.

[1] Time before the ext4 driver is initialized.
[2] Measured as cat /proc/meminfo | grep Slab.
[3] Measured as iperf -s & iperf -c 127.0.0.1 -t 30.

====== Some notes

A few notes:

1. The patchset can be found here:
https://github.com/xairy/kasan-prototype/tree/khwasan

2. Building requires a recent LLVM version (r330044 or later).

3. Stack instrumentation is not supported yet (in progress).

4. There are still a few TODOs in the code, that need to be addressed.

====== Changes

Changes in RFC v3:
- Renamed CONFIG_KASAN_CLASSIC and CONFIG_KASAN_TAGS to CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW respectively.
- Switch to -fsanitize=kernel-hwaddress instead of -fsanitize=hwaddress.
- Removed unnecessary excessive shadow initialization.
- Removed khwasan_enabled flag (it’s not needed since KHWASAN is initialized before any slab caches are used).
- Split out kasan_report.c and khwasan_report.c from report.c.
- Moved more common KASAN and KHWASAN functions to common.c.
- Added tagging to pagealloc.
- Rebased onto 4.17-rc1.
- Temporarily dropped patch that adds kvm support (arm64 + kvm + clang combo is broken right now (https://lkml.org/lkml/2018/4/19/775)).

Changes in RFC v2:
- Removed explicit casts to u8 * for kasan_mem_to_shadow() calls.
- Introduced KASAN_TCR_FLAGS for setting the TCR_TBI1 flag.
- Added a comment regarding the non-atomic RMW sequence in khwasan_random_tag().
- Made all tag related functions accept const void *.
- Untagged pointers in __kimg_to_phys, which is used by virt_to_phys.
- Untagged pointers in show_ptr in fault handling logic.
- Untagged pointers passed to KVM.
- Added two reserved tag values: 0xFF and 0xFE.
- Used the reserved tag 0xFF to disable validity checking (to resolve the issue with pointer tag being lost after page_address + kmap usage).
- Used the reserved tag 0xFE to mark redzones and freed objects.
- Added mnemonics for esr manipulation in KHWASAN brk handler.
- Added a comment about the -recover flag.
- Some minor cleanups and fixes.
- Rebased onto 3215b9d5 (4.16-rc6+).
- Tested on real hardware (Odroid C2 board).
- Added better benchmarks.

Andrey Konovalov (15):
khwasan: move common kasan and khwasan code to common.c
khwasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW khwasan, arm64: adjust shadow size for CONFIG_KASAN_HW
khwasan: initialize shadow to 0xff
khwasan, arm64: untag virt address in __kimg_to_phys khwasan, arm64: fix up fault handling logic
khwasan: add tag related helper functions
khwasan, arm64: enable top byte ignore for the kernel khwasan, mm: perform untagged pointers comparison in krealloc
khwasan: split out kasan_report.c from report.c
khwasan: add bug reporting routines
khwasan: add hooks implementation
khwasan, arm64: add brk handler for inline instrumentation khwasan, mm, arm64: tag non slab memory allocated via pagealloc
khwasan: update kasan documentation

 Documentation/dev-tools/kasan.rst      | 212 +++++----
 arch/arm64/Kconfig                     |   1 +
 arch/arm64/Makefile                    |   2 +-
 arch/arm64/include/asm/brk-imm.h       |   2 +
 arch/arm64/include/asm/memory.h        |  35 +-
 arch/arm64/include/asm/pgtable-hwdef.h |   1 +
 arch/arm64/kernel/traps.c              |  69 ++-
 arch/arm64/mm/fault.c                  |   3 +
 arch/arm64/mm/kasan_init.c             |  18 +-
 arch/arm64/mm/proc.S                   |   8 +-
 include/linux/compiler-clang.h         |   5 +-
 include/linux/compiler-gcc.h           |   4 +
 include/linux/compiler.h               |   3 +-
 include/linux/kasan.h                  |  50 ++-
 include/linux/mm.h                     |  29 ++
 include/linux/page-flags-layout.h      |  10 +
 lib/Kconfig.kasan                      |  68 ++-
 mm/cma.c                               |   1 +
 mm/kasan/Makefile                      |   9 +-
 mm/kasan/common.c                      | 576 +++++++++++++++++++++++++
 mm/kasan/kasan.c                       | 493 +--------------------
 mm/kasan/kasan.h                       |  94 +++-
 mm/kasan/kasan_report.c                | 155 +++++++
 mm/kasan/khwasan.c                     | 163 +++++++
 mm/kasan/khwasan_report.c              |  60 +++
 mm/kasan/report.c                      | 271 ++++--------
 mm/page_alloc.c                        |   1 +
 mm/slab_common.c                       |   2 +-
 mm/slub.c                              |   2 +-
 scripts/Makefile.kasan                 |  27 +-
 30 files changed, 1558 insertions(+), 816 deletions(-)
 create mode 100644 mm/kasan/common.c
 create mode 100644 mm/kasan/kasan_report.c
 create mode 100644 mm/kasan/khwasan.c
 create mode 100644 mm/kasan/khwasan_report.c

Signature · 6 lines

2.17.0.484.g0c8726318c-goog

_______________________________________________
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[email protected]
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Andrey Konovalov

author

2018-04-20 14:38 UTC #1 lore raw

RFC PATCH v3 1/15 khwasan: move common kasan and khwasan code to common.c

KHWASAN will reuse a significant part of KASAN code, so move the common parts to common.c without any functional changes.

Signed-off-by Andrey Konovalov <[email protected]>

---
 mm/kasan/Makefile |   5 +-
 mm/kasan/common.c | 524 ++++++++++++++++++++++++++++++++++++++++++++++
 mm/kasan/kasan.c  | 493 +------------------------------------------
 mm/kasan/kasan.h  |   6 +
 4 files changed, 537 insertions(+), 491 deletions(-)
 create mode 100644 mm/kasan/common.c

mm/kasan/Makefile +4 -1

index 3289db38bc87..a6df14bffb6b 100644
@@ -1,11 +1,14 @@
 # SPDX-License-Identifier: GPL-2.0
 KASAN_SANITIZE := n
+UBSAN_SANITIZE_common.o := n
 UBSAN_SANITIZE_kasan.o := n
 KCOV_INSTRUMENT := n
 
 CFLAGS_REMOVE_kasan.o = -pg
 # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
 # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
+
+CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
-obj-y := kasan.o report.o kasan_init.o quarantine.o
+obj-y := common.o kasan.o report.o kasan_init.o quarantine.o

mm/kasan/common.c new file +524 -0

524 lines not on this page · raw message

mm/kasan/kasan.c +3 ~~-490~~

533 lines not on this page · raw message

mm/kasan/kasan.h +6 -0

index c12dcfde2ebd..c39039308b98 100644
@@ -98,6 +98,7 @@ struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
 					const void *object);
 struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
 					const void *object);
+unsigned int optimal_redzone(unsigned int object_size);
 
 static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
 {

@@ -105,6 +106,11 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
 		<< KASAN_SHADOW_SCALE_SHIFT);
 }
 
+void kasan_poison_shadow(const void *address, size_t size, u8 value);
+
+void check_memory_region(unsigned long addr, size_t size, bool write,
+				unsigned long ret_ip);
+
 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);

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #2 lore raw

RFC PATCH v3 2/15 khwasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW

In reply to Andrey Konovalov

This commit splits the current CONFIG_KASAN config option into two:
1. CONFIG_KASAN_GENERIC, that enables the generic software-only KASAN version (the one that exists now);
2. CONFIG_KASAN_HW, that enables KHWASAN.

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

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

This commit also adds empty placeholder (for now) implementation of KHWASAN 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 <[email protected]>

---
 arch/arm64/Kconfig             |  1 +
 include/linux/compiler-clang.h |  5 ++-
 include/linux/compiler-gcc.h   |  4 ++
 include/linux/compiler.h       |  3 +-
 include/linux/kasan.h          | 16 ++++++--
 lib/Kconfig.kasan              | 68 ++++++++++++++++++++++--------
 mm/kasan/Makefile              |  6 ++-
 mm/kasan/kasan.h               | 11 ++++-
 mm/kasan/khwasan.c             | 75 ++++++++++++++++++++++++++++++++++
 mm/slub.c                      |  2 +-
 scripts/Makefile.kasan         | 27 +++++++++++-
 11 files changed, 192 insertions(+), 26 deletions(-)
 create mode 100644 mm/kasan/khwasan.c

arch/arm64/Kconfig +1 -0

index eb2cf4938f6d..6553aaa61e6a 100644
@@ -88,6 +88,7 @@ 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_HW 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

include/linux/compiler-clang.h +4 -1

index 7d98e263e048..72681c6fd418 100644
@@ -21,13 +21,16 @@
 #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
 
 #undef __no_sanitize_address
 #define __no_sanitize_address __attribute__((no_sanitize("address")))
 
+#undef __no_sanitize_hwaddress
+#define __no_sanitize_hwaddress __attribute__((no_sanitize("hwaddress")))
+
 /* Clang doesn't have a way to turn it off per-function, yet. */
 #ifdef __noretpoline
 #undef __noretpoline

include/linux/compiler-gcc.h +4 -0

index b4bf73f5e38f..00a51feb786d 100644
@@ -338,6 +338,10 @@
 #define __no_sanitize_address
 #endif
 
+#if !defined(__no_sanitize_hwaddress)
+#define __no_sanitize_hwaddress	/* gcc doesn't support KHWASAN */
+#endif
+
 /*
  * A trick to suppress uninitialized variable warning without generating any
  * code

include/linux/compiler.h +2 -1

index ab4711c63601..6142bae513e8 100644
@@ -195,7 +195,8 @@ void __read_once_size(const volatile void *p, void *res, int size)
  * 	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
  * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
  */
-# define __no_kasan_or_inline __no_sanitize_address __maybe_unused
+# define __no_kasan_or_inline __no_sanitize_address __no_sanitize_hwaddress \
+			      __maybe_unused
 #else
 # define __no_kasan_or_inline __always_inline
 #endif

include/linux/kasan.h +12 -4

index cbdc54543803..6608aa9b35ac 100644
@@ -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);

@@ -94,8 +92,6 @@ 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,

@@ -141,4 +137,16 @@ 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 +52 ~~-16~~

101 lines not on this page · raw message

mm/kasan/Makefile +5 -1

index a6df14bffb6b..14955add96d3 100644
@@ -2,6 +2,7 @@
 KASAN_SANITIZE := n
 UBSAN_SANITIZE_common.o := n
 UBSAN_SANITIZE_kasan.o := n
+UBSAN_SANITIZE_khwasan.o := n
 KCOV_INSTRUMENT := n
 
 CFLAGS_REMOVE_kasan.o = -pg

@@ -10,5 +11,8 @@ CFLAGS_REMOVE_kasan.o = -pg
 
 CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
+CFLAGS_khwasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
-obj-y := common.o kasan.o report.o kasan_init.o quarantine.o
+obj-$(CONFIG_KASAN) := common.o kasan_init.o report.o
+obj-$(CONFIG_KASAN_GENERIC) += kasan.o quarantine.o
+obj-$(CONFIG_KASAN_HW) += khwasan.o

mm/kasan/kasan.h +10 -1

index c39039308b98..5091a433f266 100644
@@ -98,7 +98,15 @@ struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
 					const void *object);
 struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
 					const void *object);
+
+#ifdef CONFIG_KASAN_GENERIC
 unsigned int optimal_redzone(unsigned int object_size);
+#else
+static inline unsigned int optimal_redzone(unsigned int object_size)
+{
+	return 0;
+}
+#endif
 
 static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
 {

@@ -115,7 +123,8 @@ 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/khwasan.c new file +75 -0

75 lines not on this page · raw message

mm/slub.c +1 -1

index 4fcd1442a761..b3118f7ea92a 100644
@@ -2989,7 +2989,7 @@ 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);

scripts/Makefile.kasan +26 -1

index 69552a39951d..47023daf5606 100644
@@ -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

@@ -45,3 +45,28 @@ endif
 CFLAGS_KASAN_NOSANITIZE := -fno-builtin
 
 endif
+
+ifdef CONFIG_KASAN_HW
+
+ifdef CONFIG_KASAN_INLINE
+    instrumentation_flags := -mllvm -hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET)
+else
+    instrumentation_flags := -mllvm -hwasan-instrument-with-calls=1
+endif
+
+CFLAGS_KASAN_MINIMAL := -fsanitize=kernel-hwaddress
+
+ifeq ($(call cc-option, $(CFLAGS_KASAN_MINIMAL) -Werror),)
+    ifneq ($(CONFIG_COMPILE_TEST),y)
+        $(warning Cannot use CONFIG_KASAN_HW: \
+            -fsanitize=hwaddress is not supported by compiler)
+    endif
+else
+    CFLAGS_KASAN := $(call cc-option, -fsanitize=kernel-hwaddress \
+        -mllvm -hwasan-instrument-stack=0 \
+        $(instrumentation_flags))
+endif
+
+CFLAGS_KASAN_NOSANITIZE := -fno-builtin
+
+endif

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #3 lore raw

RFC PATCH v3 3/15 khwasan, arm64: adjust shadow size for CONFIG_KASAN_HW

In reply to Andrey Konovalov

KWHASAN uses 1 shadow byte for 16 bytes of kernel memory, so it requires 1/16th of the kernel virtual address space for the shadow memory.

This commit sets KASAN_SHADOW_SCALE_SHIFT to 4 when KHWASAN is enabled.

Signed-off-by Andrey Konovalov <[email protected]>

---
 arch/arm64/Makefile             |  2 +-
 arch/arm64/include/asm/memory.h | 13 +++++++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

arch/arm64/Makefile +1 -1

index 15402861bb59..49092d763673 100644
@@ -95,7 +95,7 @@ endif
 # KASAN_SHADOW_OFFSET = VA_START + (1 << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
 #				 - (1 << (64 - KASAN_SHADOW_SCALE_SHIFT))
 # in 32-bit arithmetic
-KASAN_SHADOW_SCALE_SHIFT := 3
+KASAN_SHADOW_SCALE_SHIFT := $(if $(CONFIG_KASAN_HW), 4, 3)
 KASAN_SHADOW_OFFSET := $(shell printf "0x%08x00000000\n" $$(( \
 	(0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 32))) \
 	+ (1 << ($(CONFIG_ARM64_VA_BITS) - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) \

arch/arm64/include/asm/memory.h +9 -4

index 49d99214f43c..6d084431b7f7 100644
@@ -74,12 +74,17 @@
 #define KERNEL_END        _end
 
 /*
- * KASAN requires 1/8th of the kernel virtual address space for the shadow
- * region. KASAN can bloat the stack significantly, so double the (minimum)
- * stack size when KASAN is in use.
+ * KASAN and KHWASAN require 1/8th and 1/16th of the kernel virtual address
+ * space for the shadow region respectively. They can bloat the stack
+ * significantly, so double the (minimum) stack size when they are in use.
  */
-#ifdef CONFIG_KASAN
+#ifdef CONFIG_KASAN_GENERIC
 #define KASAN_SHADOW_SCALE_SHIFT 3
+#endif
+#ifdef CONFIG_KASAN_HW
+#define KASAN_SHADOW_SCALE_SHIFT 4
+#endif
+#ifdef CONFIG_KASAN
 #define KASAN_SHADOW_SIZE	(UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
 #define KASAN_THREAD_SHIFT	1
 #else

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #4 lore raw

RFC PATCH v3 4/15 khwasan: initialize shadow to 0xff

In reply to Andrey Konovalov

A KHWASAN shadow memory cell contains a memory tag, that corresponds to the tag in the top byte of the pointer, that points to that memory. The native top byte value of kernel pointers is 0xff, so with KHWASAN we need to initialize shadow memory to 0xff. This commit does that.

Signed-off-by Andrey Konovalov <[email protected]>

---
 arch/arm64/mm/kasan_init.c | 16 ++++++++++++++--
 include/linux/kasan.h      |  8 ++++++++
 mm/kasan/common.c          |  3 ++-
 3 files changed, 24 insertions(+), 3 deletions(-)

arch/arm64/mm/kasan_init.c +14 -2

index dabfc1ecda3d..85b21292ee68 100644
@@ -44,6 +44,15 @@ static phys_addr_t __init kasan_alloc_zeroed_page(int node)
 	return __pa(p);
 }
 
+static phys_addr_t __init kasan_alloc_raw_page(int node)
+{
+	void *p = memblock_virt_alloc_try_nid_raw(PAGE_SIZE, PAGE_SIZE,
+						  __pa(MAX_DMA_ADDRESS),
+						  MEMBLOCK_ALLOC_ACCESSIBLE,
+						  node);
+	return __pa(p);
+}
+
 static pte_t *__init kasan_pte_offset(pmd_t *pmdp, unsigned long addr, int node,
 				      bool early)
 {

@@ -89,7 +98,9 @@ static void __init kasan_pte_populate(pmd_t *pmdp, unsigned long addr,
 
 	do {
 		phys_addr_t page_phys = early ? __pa_symbol(kasan_zero_page)
-					      : kasan_alloc_zeroed_page(node);
+					      : kasan_alloc_raw_page(node);
+		if (!early)
+			memset(__va(page_phys), KASAN_SHADOW_INIT, PAGE_SIZE);
 		next = addr + PAGE_SIZE;
 		set_pte(ptep, pfn_pte(__phys_to_pfn(page_phys), PAGE_KERNEL));
 	} while (ptep++, addr = next, addr != end && pte_none(READ_ONCE(*ptep)));

@@ -139,6 +150,7 @@ asmlinkage void __init kasan_early_init(void)
 		KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
 	BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_START, PGDIR_SIZE));
 	BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE));
+
 	kasan_pgd_populate(KASAN_SHADOW_START, KASAN_SHADOW_END, NUMA_NO_NODE,
 			   true);
 }

@@ -235,7 +247,7 @@ void __init kasan_init(void)
 		set_pte(&kasan_zero_pte[i],
 			pfn_pte(sym_to_pfn(kasan_zero_page), PAGE_KERNEL_RO));
 
-	memset(kasan_zero_page, 0, PAGE_SIZE);
+	memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
 	cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
 
 	/* At this point kasan is fully initialized. Enable error messages */

include/linux/kasan.h +8 -0

index 6608aa9b35ac..336385baf926 100644
@@ -139,6 +139,8 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
 
 #ifdef CONFIG_KASAN_GENERIC
 
+#define KASAN_SHADOW_INIT 0
+
 void kasan_cache_shrink(struct kmem_cache *cache);
 void kasan_cache_shutdown(struct kmem_cache *cache);

@@ -149,4 +151,10 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
 
 #endif /* CONFIG_KASAN_GENERIC */
 
+#ifdef CONFIG_KASAN_HW
+
+#define KASAN_SHADOW_INIT 0xFF
+
+#endif /* CONFIG_KASAN_HW */
+
 #endif /* LINUX_KASAN_H */

mm/kasan/common.c +2 -1

index ebb48415e4cf..0c1159feaf5e 100644
@@ -454,11 +454,12 @@ int kasan_module_alloc(void *addr, size_t size)
 
 	ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
 			shadow_start + shadow_size,
-			GFP_KERNEL | __GFP_ZERO,
+			GFP_KERNEL,
 			PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
 			__builtin_return_address(0));
 
 	if (ret) {
+		__memset(ret, KASAN_SHADOW_INIT, shadow_size);
 		find_vm_area(addr)->flags |= VM_KASAN;
 		kmemleak_ignore(ret);
 		return 0;

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #5 lore raw

RFC PATCH v3 5/15 khwasan, arm64: untag virt address in __kimg_to_phys

In reply to Andrey Konovalov

__kimg_to_phys (which is used by virt_to_phys) assumes that the top byte of the address is 0xff, which isn't always the case with KHWASAN enabled. The solution is to reset the tag in __kimg_to_phys.

__lm_to_phys doesn't require any fixups, as it zeroes out the top byte with the current implementation.

Signed-off-by Andrey Konovalov <[email protected]>

---
 arch/arm64/include/asm/memory.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

arch/arm64/include/asm/memory.h +11 -0

index 6d084431b7f7..f206273469b5 100644
@@ -92,6 +92,12 @@
 #define KASAN_THREAD_SHIFT	0
 #endif
 
+#ifdef CONFIG_KASAN_HW
+#define KASAN_TAG_SHIFTED(tag)		((unsigned long)(tag) << 56)
+#define KASAN_SET_TAG(addr, tag)	(((addr) & ~KASAN_TAG_SHIFTED(0xff)) | \
+						KASAN_TAG_SHIFTED(tag))
+#endif
+
 #define MIN_THREAD_SHIFT	(14 + KASAN_THREAD_SHIFT)
 
 /*

@@ -225,7 +231,12 @@ static inline unsigned long kaslr_offset(void)
 #define __is_lm_address(addr)	(!!((addr) & BIT(VA_BITS - 1)))
 
 #define __lm_to_phys(addr)	(((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
+
+#ifdef CONFIG_KASAN_HW
+#define __kimg_to_phys(addr)	(KASAN_SET_TAG((addr), 0xff) - kimage_voffset)
+#else
 #define __kimg_to_phys(addr)	((addr) - kimage_voffset)
+#endif
 
 #define __virt_to_phys_nodebug(x) ({					\
 	phys_addr_t __x = (phys_addr_t)(x);				\

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #6 lore raw

RFC PATCH v3 6/15 khwasan, arm64: fix up fault handling logic

In reply to Andrey Konovalov

show_pte in arm64 fault handling relies on the fact that the top byte of a kernel pointer is 0xff, which isn't always the case with KHWASAN enabled. Reset the top byte.

Signed-off-by Andrey Konovalov <[email protected]>

---
 arch/arm64/mm/fault.c | 3 +++
 1 file changed, 3 insertions(+)

arch/arm64/mm/fault.c +3 -0

index 4165485e8b6e..e834fe76f5d2 100644
@@ -32,6 +32,7 @@
 #include <linux/perf_event.h>
 #include <linux/preempt.h>
 #include <linux/hugetlb.h>
+#include <linux/kasan.h>
 
 #include <asm/bug.h>
 #include <asm/cmpxchg.h>

@@ -134,6 +135,8 @@ void show_pte(unsigned long addr)
 	pgd_t *pgdp;
 	pgd_t pgd;
 
+	addr = (unsigned long)khwasan_reset_tag((void *)addr);
+
 	if (addr < TASK_SIZE) {
 		/* TTBR0 */
 		mm = current->active_mm;

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #7 lore raw

RFC PATCH v3 7/15 khwasan: add tag related helper functions

In reply to Andrey Konovalov

This commit adds a few helper functions, that are meant to be used to work with tags embedded in the top byte of kernel pointers: to set, to get or to reset (set to 0xff) the top byte.

Signed-off-by Andrey Konovalov <[email protected]>

---
 arch/arm64/mm/kasan_init.c |  2 ++
 include/linux/kasan.h      | 23 ++++++++++++++++
 mm/kasan/kasan.h           | 55 ++++++++++++++++++++++++++++++++++++++
 mm/kasan/khwasan.c         | 48 +++++++++++++++++++++++++++++++++
 4 files changed, 128 insertions(+)

arch/arm64/mm/kasan_init.c +2 -0

index 85b21292ee68..8ef9b1bc6d81 100644
@@ -250,6 +250,8 @@ void __init kasan_init(void)
 	memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
 	cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
 
+	khwasan_init();
+
 	/* At this point kasan is fully initialized. Enable error messages */
 	init_task.kasan_depth = 0;
 	pr_info("KernelAddressSanitizer initialized\n");

include/linux/kasan.h +23 -0

index 336385baf926..d7624b879d86 100644
@@ -155,6 +155,29 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
 
 #define KASAN_SHADOW_INIT 0xFF
 
+void khwasan_init(void);
+
+void *khwasan_set_tag(const void *addr, u8 tag);
+u8 khwasan_get_tag(const void *addr);
+void *khwasan_reset_tag(const void *ptr);
+
+#else /* CONFIG_KASAN_HW */
+
+static inline void khwasan_init(void) { }
+
+static inline void *khwasan_set_tag(const void *addr, u8 tag)
+{
+	return (void *)addr;
+}
+static inline u8 khwasan_get_tag(const void *addr)
+{
+	return 0xFF;
+}
+static inline void *khwasan_reset_tag(const void *ptr)
+{
+	return (void *)ptr;
+}
+
 #endif /* CONFIG_KASAN_HW */
 
 #endif /* LINUX_KASAN_H */

mm/kasan/kasan.h +55 -0

67 lines not on this page · raw message

mm/kasan/khwasan.c +48 -0

54 lines not on this page · raw message

Signature · 6 lines

2.17.0.484.g0c8726318c-goog

_______________________________________________
kvmarm mailing list
[email protected]
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

Andrey Konovalov

author

2018-04-20 14:38 UTC #8 lore raw

RFC PATCH v3 8/15 khwasan, arm64: enable top byte ignore for the kernel

In reply to Andrey Konovalov

KHWASAN uses the Top Byte Ignore feature of arm64 CPUs to store a pointer tag in the top byte of each pointer. This commit enables the TCR_TBI1 bit, which enables Top Byte Ignore for the kernel, when KHWASAN is used.

Signed-off-by Andrey Konovalov <[email protected]>

---
 arch/arm64/include/asm/pgtable-hwdef.h | 1 +
 arch/arm64/mm/proc.S                   | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

arch/arm64/include/asm/pgtable-hwdef.h +1 -0

index fd208eac9f2a..483aceedad76 100644
@@ -289,6 +289,7 @@
 #define TCR_A1			(UL(1) << 22)
 #define TCR_ASID16		(UL(1) << 36)
 #define TCR_TBI0		(UL(1) << 37)
+#define TCR_TBI1		(UL(1) << 38)
 #define TCR_HA			(UL(1) << 39)
 #define TCR_HD			(UL(1) << 40)
 #define TCR_NFD1		(UL(1) << 54)

arch/arm64/mm/proc.S +7 -1

index 5f9a73a4452c..f3dfcd74a285 100644
@@ -47,6 +47,12 @@
 /* PTWs cacheable, inner/outer WBWA */
 #define TCR_CACHE_FLAGS	TCR_IRGN_WBWA | TCR_ORGN_WBWA
 
+#ifdef CONFIG_KASAN_HW
+#define TCR_KASAN_FLAGS TCR_TBI1
+#else
+#define TCR_KASAN_FLAGS 0
+#endif
+
 #define MAIR(attr, mt)	((attr) << ((mt) * 8))
 
 /*

@@ -439,7 +445,7 @@ ENTRY(__cpu_setup)
 	 */
 	ldr	x10, =TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
 			TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
-			TCR_TBI0 | TCR_A1
+			TCR_TBI0 | TCR_A1 | TCR_KASAN_FLAGS
 	tcr_set_idmap_t0sz	x10, x9
 
 	/*

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #9 lore raw

RFC PATCH v3 9/15 khwasan, mm: perform untagged pointers comparison in krealloc

In reply to Andrey Konovalov

The krealloc function checks where the same buffer was reused or a new one allocated by comparing kernel pointers. KHWASAN changes memory tag on the krealloc'ed chunk of memory and therefore also changes the pointer tag of the returned pointer. Therefore we need to perform comparison on untagged (with tags reset) pointers to check whether it's the same memory region or not.

Signed-off-by Andrey Konovalov <[email protected]>

---
 mm/slab_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

mm/slab_common.c +1 -1

index 0582004351c4..451b094b8c5b 100644
@@ -1478,7 +1478,7 @@ void *krealloc(const void *p, size_t new_size, gfp_t flags)
 	}
 
 	ret = __do_krealloc(p, new_size, flags);
-	if (ret && p != ret)
+	if (ret && khwasan_reset_tag(p) != khwasan_reset_tag(ret))
 		kfree(p);
 
 	return ret;

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #10 lore raw

RFC PATCH v3 10/15 khwasan: split out kasan_report.c from report.c

In reply to Andrey Konovalov

This patch moves KASAN specific error reporting routines to kasan_report.c without any functional changes, leaving common error reporting code in report.c to be later reused by KHWASAN.

Signed-off-by Andrey Konovalov <[email protected]>

---
 mm/kasan/Makefile         |   4 +-
 mm/kasan/kasan.h          |   7 ++
 mm/kasan/kasan_report.c   | 158 +++++++++++++++++++++++++
 mm/kasan/khwasan_report.c |  39 +++++++
 mm/kasan/report.c         | 234 +++++++++-----------------------------
 5 files changed, 257 insertions(+), 185 deletions(-)
 create mode 100644 mm/kasan/kasan_report.c
 create mode 100644 mm/kasan/khwasan_report.c

mm/kasan/Makefile +2 -2

index 14955add96d3..7ef536390365 100644
@@ -14,5 +14,5 @@ CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 CFLAGS_khwasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
 obj-$(CONFIG_KASAN) := common.o kasan_init.o report.o
-obj-$(CONFIG_KASAN_GENERIC) += kasan.o quarantine.o
-obj-$(CONFIG_KASAN_HW) += khwasan.o
+obj-$(CONFIG_KASAN_GENERIC) += kasan.o kasan_report.o quarantine.o
+obj-$(CONFIG_KASAN_HW) += khwasan.o khwasan_report.o

mm/kasan/kasan.h +7 -0

index cd51ae9d8149..a76aee9e095f 100644
@@ -118,11 +118,18 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
 		<< KASAN_SHADOW_SCALE_SHIFT);
 }
 
+static inline bool addr_has_shadow(const void *addr)
+{
+	return (addr >= kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
+}
+
 void kasan_poison_shadow(const void *address, size_t size, u8 value);
 
 void check_memory_region(unsigned long addr, size_t size, bool write,
 				unsigned long ret_ip);
 
+const char *get_bug_type(struct kasan_access_info *info);
+
 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);

mm/kasan/kasan_report.c new file +158 -0

158 lines not on this page · raw message

mm/kasan/khwasan_report.c new file +39 -0

new file mode 100644
index 000000000000..2edbc3c76be5
@@ -0,0 +1,39 @@
+/*
+ * This file contains KHWASAN specific error reporting code.
+ *
+ * Copyright (c) 2014 Samsung Electronics Co., Ltd.
+ * Author: Andrey Ryabinin <[email protected]>
+ *
+ * Some code borrowed from https://github.com/xairy/kasan-prototype by
+ *        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.
+ *
+ */
+
+#include <linux/bitops.h>
+#include <linux/ftrace.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/printk.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/stackdepot.h>
+#include <linux/stacktrace.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/kasan.h>
+#include <linux/module.h>
+
+#include <asm/sections.h>
+
+#include "kasan.h"
+#include "../slab.h"
+
+const char *get_bug_type(struct kasan_access_info *info)
+{
+	return "invalid-access";
+}

mm/kasan/report.c +51 ~~-183~~

315 lines not on this page · raw message

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #11 lore raw

RFC PATCH v3 11/15 khwasan: add bug reporting routines

In reply to Andrey Konovalov

This commit adds rountines, that print KHWASAN error reports. Those are quite similar to KASAN, the difference is:

1. The way KHWASAN finds the first bad shadow cell (with a mismatching tag). KHWASAN compares memory tags from the shadow memory to the pointer tag.

2. KHWASAN reports all bugs with the "KASAN: invalid-access" header. This is done, so various external tools that already parse the kernel logs looking for KASAN reports wouldn't need to be changed.

Signed-off-by Andrey Konovalov <[email protected]>

---
 include/linux/kasan.h     |  3 +++
 mm/kasan/kasan.h          |  7 +++++
 mm/kasan/kasan_report.c   |  7 ++---
 mm/kasan/khwasan_report.c | 21 +++++++++++++++
 mm/kasan/report.c         | 57 +++++++++++++++++++++------------------
 5 files changed, 64 insertions(+), 31 deletions(-)

include/linux/kasan.h +3 -0

index d7624b879d86..e209027f3b52 100644
@@ -161,6 +161,9 @@ void *khwasan_set_tag(const void *addr, u8 tag);
 u8 khwasan_get_tag(const void *addr);
 void *khwasan_reset_tag(const void *ptr);
 
+void kasan_report(unsigned long addr, size_t size,
+			bool write, unsigned long ip);
+
 #else /* CONFIG_KASAN_HW */
 
 static inline void khwasan_init(void) { }

mm/kasan/kasan.h +7 -0

index a76aee9e095f..620941d1e84f 100644
@@ -128,8 +128,15 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value);
 void check_memory_region(unsigned long addr, size_t size, bool write,
 				unsigned long ret_ip);
 
+void *find_first_bad_addr(void *addr, size_t size);
 const char *get_bug_type(struct kasan_access_info *info);
 
+#ifdef CONFIG_KASAN_HW
+void print_tags(u8 addr_tag, const void *addr);
+#else
+static inline void print_tags(u8 addr_tag, const void *addr) { }
+#endif
+
 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);

mm/kasan/kasan_report.c +2 -5

index 2d8decbecbd5..fdf2d77e3125 100644
@@ -33,10 +33,10 @@
 #include "kasan.h"
 #include "../slab.h"
 
-static const void *find_first_bad_addr(const void *addr, size_t size)
+void *find_first_bad_addr(void *addr, size_t size)
 {
 	u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
-	const void *first_bad_addr = addr;
+	void *first_bad_addr = addr;
 
 	while (!shadow_val && first_bad_addr < addr + size) {
 		first_bad_addr += KASAN_SHADOW_SCALE_SIZE;

@@ -50,9 +50,6 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info)
 	const char *bug_type = "unknown-crash";
 	u8 *shadow_addr;
 
-	info->first_bad_addr = find_first_bad_addr(info->access_addr,
-						info->access_size);
-
 	shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);
 
 	/*

mm/kasan/khwasan_report.c +21 -0

index 2edbc3c76be5..51238b404b08 100644
@@ -37,3 +37,24 @@ const char *get_bug_type(struct kasan_access_info *info)
 {
 	return "invalid-access";
 }
+
+void *find_first_bad_addr(void *addr, size_t size)
+{
+	u8 tag = get_tag(addr);
+	void *untagged_addr = reset_tag(addr);
+	u8 *shadow = (u8 *)kasan_mem_to_shadow(untagged_addr);
+	void *first_bad_addr = untagged_addr;
+
+	while (*shadow == tag && first_bad_addr < untagged_addr + size) {
+		first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
+		shadow = (u8 *)kasan_mem_to_shadow(first_bad_addr);
+	}
+	return first_bad_addr;
+}
+
+void print_tags(u8 addr_tag, const void *addr)
+{
+	u8 *shadow = (u8 *)kasan_mem_to_shadow(addr);
+
+	pr_err("Pointer tag: [%02x], memory tag: [%02x]\n", addr_tag, *shadow);
+}

mm/kasan/report.c +31 ~~-26~~

89 lines not on this page · raw message

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #12 lore raw

RFC PATCH v3 12/15 khwasan: add hooks implementation

In reply to Andrey Konovalov

This commit adds KHWASAN specific hooks implementation and adjusts common KASAN and KHWASAN ones.

1. When a new slab cache is created, KHWASAN rounds up the size of the objects in this cache to KASAN_SHADOW_SCALE_SIZE (== 16).

2. On each kmalloc KHWASAN generates a random tag, sets the shadow memory, that corresponds to this object to this tag, and embeds this tag value into the top byte of the returned pointer.

3. On each kfree KHWASAN poisons the shadow memory with a random tag to allow detection of use-after-free bugs.

The rest of the logic of the hook implementation is very much similar to the one provided by KASAN. KHWASAN saves allocation and free stack metadata to the slab object the same was KASAN does this.

Signed-off-by Andrey Konovalov <[email protected]>

---
 mm/kasan/common.c  | 73 ++++++++++++++++++++++++++++++++++++----------
 mm/kasan/kasan.h   |  8 +++++
 mm/kasan/khwasan.c | 40 +++++++++++++++++++++++++
 3 files changed, 105 insertions(+), 16 deletions(-)

mm/kasan/common.c +57 ~~-16~~

index 0c1159feaf5e..0654bf97257b 100644
@@ -140,6 +140,9 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
 {
 	void *shadow_start, *shadow_end;
 
+	/* Perform shadow offset calculation based on untagged address */
+	address = reset_tag(address);
+
 	shadow_start = kasan_mem_to_shadow(address);
 	shadow_end = kasan_mem_to_shadow(address + size);

@@ -148,11 +151,15 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
 
 void kasan_unpoison_shadow(const void *address, size_t size)
 {
-	kasan_poison_shadow(address, size, 0);
+	kasan_poison_shadow(address, size, get_tag(address));
 
 	if (size & KASAN_SHADOW_MASK) {
 		u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
-		*shadow = size & KASAN_SHADOW_MASK;
+
+		if (IS_ENABLED(CONFIG_KASAN_HW))
+			*shadow = get_tag(address);
+		else
+			*shadow = size & KASAN_SHADOW_MASK;
 	}
 }

@@ -216,6 +223,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 			slab_flags_t *flags)
 {
 	unsigned int orig_size = *size;
+	unsigned int redzone_size = 0;
 	int redzone_adjust;
 
 	/* Add alloc meta. */

@@ -223,20 +231,20 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 	*size += sizeof(struct kasan_alloc_meta);
 
 	/* Add free meta. */
-	if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
-	    cache->object_size < sizeof(struct kasan_free_meta)) {
+	if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+	    (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
+	     cache->object_size < sizeof(struct kasan_free_meta))) {
 		cache->kasan_info.free_meta_offset = *size;
 		*size += sizeof(struct kasan_free_meta);
 	}
-	redzone_adjust = optimal_redzone(cache->object_size) -
-		(*size - cache->object_size);
 
+	redzone_size = optimal_redzone(cache->object_size);
+	redzone_adjust = redzone_size -	(*size - cache->object_size);
 	if (redzone_adjust > 0)
 		*size += redzone_adjust;
 
 	*size = min_t(unsigned int, KMALLOC_MAX_SIZE,
-			max(*size, cache->object_size +
-					optimal_redzone(cache->object_size)));
+			max(*size, cache->object_size + redzone_size));
 
 	/*
 	 * If the metadata doesn't fit, don't enable KASAN at all.

@@ -306,18 +314,30 @@ void kasan_init_slab_obj(struct kmem_cache *cache, const void *object)
 
 void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
 {
-	return kasan_kmalloc(cache, object, cache->object_size, flags);
+	object = kasan_kmalloc(cache, object, cache->object_size, flags);
+	if (IS_ENABLED(CONFIG_KASAN_HW) && unlikely(cache->ctor)) {
+		/*
+		 * Cache constructor might use object's pointer value to
+		 * initialize some of its fields.
+		 */
+		cache->ctor(object);
+	}
+	return object;
 }
 
 static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
 			      unsigned long ip, bool quarantine)
 {
 	s8 shadow_byte;
+	u8 tag;
 	unsigned long rounded_up_size;
 
+	tag = get_tag(object);
+	object = reset_tag(object);
+
 	if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
 	    object)) {
-		kasan_report_invalid_free(object, ip);
+		kasan_report_invalid_free(set_tag(object, tag), ip);
 		return true;
 	}

@@ -326,20 +346,29 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
 		return false;
 
 	shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
+#ifdef CONFIG_KASAN_GENERIC
 	if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
 		kasan_report_invalid_free(object, ip);
 		return true;
 	}
+#else
+	if (tag != (u8)shadow_byte) {
+		kasan_report_invalid_free(set_tag(object, tag), ip);
+		return true;
+	}
+#endif
 
 	rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
 	kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
 
-	if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN)))
+	if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
+			unlikely(!(cache->flags & SLAB_KASAN)))
 		return false;
 
 	set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
 	quarantine_put(get_free_info(cache, object), cache);
-	return true;
+
+	return IS_ENABLED(CONFIG_KASAN_GENERIC);
 }
 
 bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)

@@ -352,6 +381,7 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
 {
 	unsigned long redzone_start;
 	unsigned long redzone_end;
+	u8 tag;
 
 	if (gfpflags_allow_blocking(flags))
 		quarantine_reduce();

@@ -364,14 +394,19 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
 	redzone_end = round_up((unsigned long)object + cache->object_size,
 				KASAN_SHADOW_SCALE_SIZE);
 
+#ifdef CONFIG_KASAN_GENERIC
 	kasan_unpoison_shadow(object, size);
+#else
+	tag = random_tag();
+	kasan_poison_shadow(object, redzone_start - (unsigned long)object, tag);
+#endif
 	kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
 		KASAN_KMALLOC_REDZONE);
 
 	if (cache->flags & SLAB_KASAN)
 		set_track(&get_alloc_info(cache, object)->alloc_track, flags);
 
-	return (void *)object;
+	return set_tag(object, tag);
 }
 EXPORT_SYMBOL(kasan_kmalloc);

@@ -380,6 +415,7 @@ void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
 	struct page *page;
 	unsigned long redzone_start;
 	unsigned long redzone_end;
+	u8 tag;
 
 	if (gfpflags_allow_blocking(flags))
 		quarantine_reduce();

@@ -392,11 +428,16 @@ void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
 				KASAN_SHADOW_SCALE_SIZE);
 	redzone_end = (unsigned long)ptr + (PAGE_SIZE << compound_order(page));
 
+#ifdef CONFIG_KASAN_GENERIC
 	kasan_unpoison_shadow(ptr, size);
+#else
+	tag = random_tag();
+	kasan_poison_shadow(ptr, redzone_start - (unsigned long)ptr, tag);
+#endif
 	kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
 		KASAN_PAGE_REDZONE);
 
-	return (void *)ptr;
+	return set_tag(ptr, tag);
 }
 
 void *kasan_krealloc(const void *object, size_t size, gfp_t flags)

@@ -421,7 +462,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
 	page = virt_to_head_page(ptr);
 
 	if (unlikely(!PageSlab(page))) {
-		if (ptr != page_address(page)) {
+		if (reset_tag(ptr) != page_address(page)) {
 			kasan_report_invalid_free(ptr, ip);
 			return;
 		}

@@ -434,7 +475,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
 
 void kasan_kfree_large(void *ptr, unsigned long ip)
 {
-	if (ptr != page_address(virt_to_head_page(ptr)))
+	if (reset_tag(ptr) != page_address(virt_to_head_page(ptr)))
 		kasan_report_invalid_free(ptr, ip);
 	/* The object will be poisoned by page_alloc. */
 }

mm/kasan/kasan.h +8 -0

index 620941d1e84f..06b70d296411 100644
@@ -12,10 +12,18 @@
 #define KHWASAN_TAG_INVALID	0xFE /* inaccessible memory tag */
 #define KHWASAN_TAG_MAX		0xFD /* maximum value for random tags */
 
+#ifdef CONFIG_KASAN_GENERIC
 #define KASAN_FREE_PAGE         0xFF  /* page was freed */
 #define KASAN_PAGE_REDZONE      0xFE  /* redzone for kmalloc_large allocations */
 #define KASAN_KMALLOC_REDZONE   0xFC  /* redzone inside slub object */
 #define KASAN_KMALLOC_FREE      0xFB  /* object was freed (kmem_cache_free/kfree) */
+#else
+#define KASAN_FREE_PAGE         KHWASAN_TAG_INVALID
+#define KASAN_PAGE_REDZONE      KHWASAN_TAG_INVALID
+#define KASAN_KMALLOC_REDZONE   KHWASAN_TAG_INVALID
+#define KASAN_KMALLOC_FREE      KHWASAN_TAG_INVALID
+#endif
+
 #define KASAN_GLOBAL_REDZONE    0xFA  /* redzone for global variable */
 
 /*

mm/kasan/khwasan.c +40 -0

index 4e253c1e4d35..b4919ef74741 100644
@@ -89,15 +89,52 @@ void *khwasan_reset_tag(const void *addr)
 void check_memory_region(unsigned long addr, size_t size, bool write,
 				unsigned long ret_ip)
 {
+	u8 tag;
+	u8 *shadow_first, *shadow_last, *shadow;
+	void *untagged_addr;
+
+	tag = get_tag((const void *)addr);
+
+	/* Ignore accesses for pointers tagged with 0xff (native kernel
+	 * pointer tag) to suppress false positives caused by kmap.
+	 *
+	 * Some kernel code was written to account for archs that don't keep
+	 * high memory mapped all the time, but rather map and unmap particular
+	 * pages when needed. Instead of storing a pointer to the kernel memory,
+	 * this code saves the address of the page structure and offset within
+	 * that page for later use. Those pages are then mapped and unmapped
+	 * with kmap/kunmap when necessary and virt_to_page is used to get the
+	 * virtual address of the page. For arm64 (that keeps the high memory
+	 * mapped all the time), kmap is turned into a page_address call.
+
+	 * The issue is that with use of the page_address + virt_to_page
+	 * sequence the top byte value of the original pointer gets lost (gets
+	 * set to KHWASAN_TAG_KERNEL (0xFF).
+	 */
+	if (tag == KHWASAN_TAG_KERNEL)
+		return;
+
+	untagged_addr = reset_tag((const void *)addr);
+	shadow_first = kasan_mem_to_shadow(untagged_addr);
+	shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
+
+	for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
+		if (*shadow != tag) {
+			kasan_report(addr, size, write, ret_ip);
+			return;
+		}
+	}
 }
 
 #define DEFINE_HWASAN_LOAD_STORE(size)					\
 	void __hwasan_load##size##_noabort(unsigned long addr)		\
 	{								\
+		check_memory_region(addr, size, false, _RET_IP_);	\
 	}								\
 	EXPORT_SYMBOL(__hwasan_load##size##_noabort);			\
 	void __hwasan_store##size##_noabort(unsigned long addr)		\
 	{								\
+		check_memory_region(addr, size, true, _RET_IP_);	\
 	}								\
 	EXPORT_SYMBOL(__hwasan_store##size##_noabort)

@@ -109,15 +146,18 @@ DEFINE_HWASAN_LOAD_STORE(16);
 
 void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
 {
+	check_memory_region(addr, size, false, _RET_IP_);
 }
 EXPORT_SYMBOL(__hwasan_loadN_noabort);
 
 void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
 {
+	check_memory_region(addr, size, true, _RET_IP_);
 }
 EXPORT_SYMBOL(__hwasan_storeN_noabort);
 
 void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
 {
+	kasan_poison_shadow((void *)addr, size, tag);
 }
 EXPORT_SYMBOL(__hwasan_tag_memory);

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #13 lore raw

RFC PATCH v3 13/15 khwasan, arm64: add brk handler for inline instrumentation

In reply to Andrey Konovalov

KHWASAN inline instrumentation mode (which embeds checks of shadow memory into the generated code, instead of inserting a callback) generates a brk instruction when a tag mismatch is detected.

This commit add a KHWASAN brk handler, that decodes the immediate value passed to the brk instructions (to extract information about the memory access that triggered the mismatch), reads the register values (x0 contains the guilty address) and reports the bug.

Signed-off-by Andrey Konovalov <[email protected]>

---
 arch/arm64/include/asm/brk-imm.h |  2 +
 arch/arm64/kernel/traps.c        | 69 +++++++++++++++++++++++++++++++-
 2 files changed, 69 insertions(+), 2 deletions(-)

arch/arm64/include/asm/brk-imm.h +2 -0

index ed693c5bcec0..e4a7013321dc 100644
@@ -16,10 +16,12 @@
  * 0x400: for dynamic BRK instruction
  * 0x401: for compile time BRK instruction
  * 0x800: kernel-mode BUG() and WARN() traps
+ * 0x9xx: KHWASAN trap (allowed values 0x900 - 0x9ff)
  */
 #define FAULT_BRK_IMM			0x100
 #define KGDB_DYN_DBG_BRK_IMM		0x400
 #define KGDB_COMPILED_DBG_BRK_IMM	0x401
 #define BUG_BRK_IMM			0x800
+#define KHWASAN_BRK_IMM			0x900
 
 #endif

arch/arm64/kernel/traps.c +67 -2

106 lines not on this page · raw message

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #14 lore raw

RFC PATCH v3 14/15 khwasan, mm, arm64: tag non slab memory allocated via pagealloc

In reply to Andrey Konovalov

KWHASAN doesn't check memory accesses through pointers tagged with 0xff. When page_address is used to get pointer to memory that corresponds to some page, the tag of the resulting pointer gets set to 0xff, even though the allocated memory might have been tagged differently.

For slab pages it's impossible to recover the correct tag to return from page_address, since the page might contain multiple slab objects tagged with different values, and we can't know in advance which one of them is going to get accessed. For non slab pages however, we can recover the tag in page_address, since the whole page was marked with the same tag.

This patch adds tagging to non slab memory allocated with pagealloc. To set the tag of the pointer returned from page_address, the tag gets stored to page->flags when the memory gets allocated.

Signed-off-by Andrey Konovalov <[email protected]>

---
 arch/arm64/include/asm/memory.h   | 11 +++++++++++
 include/linux/mm.h                | 29 +++++++++++++++++++++++++++++
 include/linux/page-flags-layout.h | 10 ++++++++++
 mm/cma.c                          |  1 +
 mm/kasan/common.c                 | 14 ++++++++++++--
 mm/page_alloc.c                   |  1 +
 6 files changed, 64 insertions(+), 2 deletions(-)

arch/arm64/include/asm/memory.h +11 -0

index f206273469b5..9ec78a44c5ff 100644
@@ -304,7 +304,18 @@ static inline void *phys_to_virt(phys_addr_t x)
 #define __virt_to_pgoff(kaddr)	(((u64)(kaddr) & ~PAGE_OFFSET) / PAGE_SIZE * sizeof(struct page))
 #define __page_to_voff(kaddr)	(((u64)(kaddr) & ~VMEMMAP_START) * PAGE_SIZE / sizeof(struct page))
 
+#ifndef CONFIG_KASAN_HW
 #define page_to_virt(page)	((void *)((__page_to_voff(page)) | PAGE_OFFSET))
+#else
+#define page_to_virt(page)	({					\
+	unsigned long __addr =						\
+		((__page_to_voff(page)) | PAGE_OFFSET);			\
+	if (!PageSlab((struct page *)page))				\
+		__addr = KASAN_SET_TAG(__addr, page_kasan_tag(page));	\
+	((void *)__addr);						\
+})
+#endif
+
 #define virt_to_page(vaddr)	((struct page *)((__virt_to_pgoff(vaddr)) | VMEMMAP_START))
 
 #define _virt_addr_valid(kaddr)	pfn_valid((((u64)(kaddr) & ~PAGE_OFFSET) \

include/linux/mm.h +29 -0

index 1ac1f06a4be6..d6d596824803 100644
@@ -770,6 +770,7 @@ int finish_mkwrite_fault(struct vm_fault *vmf);
 #define NODES_PGOFF		(SECTIONS_PGOFF - NODES_WIDTH)
 #define ZONES_PGOFF		(NODES_PGOFF - ZONES_WIDTH)
 #define LAST_CPUPID_PGOFF	(ZONES_PGOFF - LAST_CPUPID_WIDTH)
+#define KASAN_TAG_PGOFF		(LAST_CPUPID_PGOFF - KASAN_TAG_WIDTH)
 
 /*
  * Define the bit shifts to access each section.  For non-existent

@@ -780,6 +781,7 @@ int finish_mkwrite_fault(struct vm_fault *vmf);
 #define NODES_PGSHIFT		(NODES_PGOFF * (NODES_WIDTH != 0))
 #define ZONES_PGSHIFT		(ZONES_PGOFF * (ZONES_WIDTH != 0))
 #define LAST_CPUPID_PGSHIFT	(LAST_CPUPID_PGOFF * (LAST_CPUPID_WIDTH != 0))
+#define KASAN_TAG_PGSHIFT	(KASAN_TAG_PGOFF * (KASAN_TAG_WIDTH != 0))
 
 /* NODE:ZONE or SECTION:ZONE is used to ID a zone for the buddy allocator */
 #ifdef NODE_NOT_IN_PAGE_FLAGS

@@ -802,6 +804,7 @@ int finish_mkwrite_fault(struct vm_fault *vmf);
 #define NODES_MASK		((1UL << NODES_WIDTH) - 1)
 #define SECTIONS_MASK		((1UL << SECTIONS_WIDTH) - 1)
 #define LAST_CPUPID_MASK	((1UL << LAST_CPUPID_SHIFT) - 1)
+#define KASAN_TAG_MASK		((1UL << KASAN_TAG_WIDTH) - 1)
 #define ZONEID_MASK		((1UL << ZONEID_SHIFT) - 1)
 
 static inline enum zone_type page_zonenum(const struct page *page)

@@ -1021,6 +1024,32 @@ static inline bool cpupid_match_pid(struct task_struct *task, int cpupid)
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
+#ifdef CONFIG_KASAN_HW
+static inline u8 page_kasan_tag(const struct page *page)
+{
+	return (page->flags >> KASAN_TAG_PGSHIFT) & KASAN_TAG_MASK;
+}
+
+static inline void page_kasan_tag_set(struct page *page, u8 tag)
+{
+	page->flags &= ~(KASAN_TAG_MASK << KASAN_TAG_PGSHIFT);
+	page->flags |= (tag & KASAN_TAG_MASK) << KASAN_TAG_PGSHIFT;
+}
+
+static inline void page_kasan_tag_reset(struct page *page)
+{
+	page_kasan_tag_set(page, 0xff);
+}
+#else
+static inline u8 page_kasan_tag(const struct page *page)
+{
+	return 0xff;
+}
+
+static inline void page_kasan_tag_set(struct page *page, u8 tag) { }
+static inline void page_kasan_tag_reset(struct page *page) { }
+#endif
+
 static inline struct zone *page_zone(const struct page *page)
 {
 	return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)];

include/linux/page-flags-layout.h +10 -0

index 7ec86bf31ce4..8dbad17664c2 100644
@@ -82,6 +82,16 @@
 #define LAST_CPUPID_WIDTH 0
 #endif
 
+#ifdef CONFIG_KASAN_HW
+#define KASAN_TAG_WIDTH 8
+#if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH+LAST_CPUPID_WIDTH+KASAN_TAG_WIDTH \
+	> BITS_PER_LONG - NR_PAGEFLAGS
+#error "KASAN: not enough bits in page flags for tag"
+#endif
+#else
+#define KASAN_TAG_WIDTH 0
+#endif
+
 /*
  * We are going to use the flags for the page to node mapping if its in
  * there.  This includes the case where there is no node, so it is implicit.

mm/cma.c +1 -0

index aa40e6c7b042..f657db289bba 100644
@@ -526,6 +526,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
 	}
 
 	trace_cma_alloc(pfn, page, count, align);
+	page_kasan_tag_reset(page);
 
 	if (ret && !(gfp_mask & __GFP_NOWARN)) {
 		pr_err("%s: alloc failed, req-size: %zu pages, ret: %d\n",

mm/kasan/common.c +12 -2

index 0654bf97257b..8d8a982d4490 100644
@@ -207,8 +207,17 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark)
 
 void kasan_alloc_pages(struct page *page, unsigned int order)
 {
+#ifdef CONFIG_KASAN_GENERIC
 	if (likely(!PageHighMem(page)))
 		kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
+#else
+	if (!PageSlab(page)) {
+		u8 tag = random_tag();
+		kasan_poison_shadow(page_address(page), PAGE_SIZE << order,
+					tag);
+		page_kasan_tag_set(page, tag);
+	}
+#endif
 }
 
 void kasan_free_pages(struct page *page, unsigned int order)

@@ -433,6 +442,7 @@ void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
 #else
 	tag = random_tag();
 	kasan_poison_shadow(ptr, redzone_start - (unsigned long)ptr, tag);
+	page_kasan_tag_set(page, tag);
 #endif
 	kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
 		KASAN_PAGE_REDZONE);

@@ -462,7 +472,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
 	page = virt_to_head_page(ptr);
 
 	if (unlikely(!PageSlab(page))) {
-		if (reset_tag(ptr) != page_address(page)) {
+		if (ptr != page_address(page)) {
 			kasan_report_invalid_free(ptr, ip);
 			return;
 		}

@@ -475,7 +485,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
 
 void kasan_kfree_large(void *ptr, unsigned long ip)
 {
-	if (reset_tag(ptr) != page_address(virt_to_head_page(ptr)))
+	if (ptr != page_address(virt_to_head_page(ptr)))
 		kasan_report_invalid_free(ptr, ip);
 	/* The object will be poisoned by page_alloc. */
 }

mm/page_alloc.c +1 -0

index 905db9d7962f..54df9c852c6e 100644
@@ -1179,6 +1179,7 @@ static void __meminit __init_single_page(struct page *page, unsigned long pfn,
 	init_page_count(page);
 	page_mapcount_reset(page);
 	page_cpupid_reset_last(page);
+	page_kasan_tag_reset(page);
 
 	INIT_LIST_HEAD(&page->lru);
 #ifdef WANT_PAGE_VIRTUAL

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Andrey Konovalov

author

2018-04-20 14:38 UTC #15 lore raw

RFC PATCH v3 15/15 khwasan: update kasan documentation

In reply to Andrey Konovalov

This patch updates KASAN documentation to reflect the addition of KHWASAN.

Signed-off-by Andrey Konovalov <[email protected]>

---
 Documentation/dev-tools/kasan.rst | 212 +++++++++++++++++-------------
 1 file changed, 122 insertions(+), 90 deletions(-)

Documentation/dev-tools/kasan.rst +122 ~~-90~~

index f7a18f274357..bd7859538b73 100644
@@ -8,11 +8,18 @@ KernelAddressSANitizer (KASAN) is a dynamic memory error detector. It provides
 a fast and comprehensive solution for finding use-after-free and out-of-bounds
 bugs.
 
-KASAN uses compile-time instrumentation for checking every memory access,
-therefore you will need a GCC version 4.9.2 or later. GCC 5.0 or later is
-required for detection of out-of-bounds accesses to stack or global variables.
+KASAN has two modes: classic KASAN (a classic version, similar to user space
+ASan) and KHWASAN (a version based on memory tagging, similar to user space
+HWASan).
 
-Currently KASAN is supported only for the x86_64 and arm64 architectures.
+KASAN uses compile-time instrumentation to insert validity checks before every
+memory access, and therefore requires a compiler version that supports that.
+For classic KASAN you need GCC version 4.9.2 or later. GCC 5.0 or later is
+required for detection of out-of-bounds accesses on stack and global variables.
+TODO: compiler requirements for KHWASAN
+
+Currently classic KASAN is supported for the x86_64, arm64 and xtensa
+architectures, and KHWASAN is supported only for arm64.
 
 Usage
 -----

@@ -21,12 +28,14 @@ To enable KASAN configure kernel with::
 
 	  CONFIG_KASAN = y
 
-and choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and
-inline are compiler instrumentation types. The former produces smaller binary
-the latter is 1.1 - 2 times faster. Inline instrumentation requires a GCC
+and choose between CONFIG_KASAN_GENERIC (to enable classic KASAN) and
+CONFIG_KASAN_HW (to enabled KHWASAN). You also need to choose choose between
+CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and inline are compiler
+instrumentation types. The former produces smaller binary the latter is
+1.1 - 2 times faster. For classic KASAN inline instrumentation requires GCC
 version 5.0 or later.
 
-KASAN works with both SLUB and SLAB memory allocators.
+Both KASAN modes work with both SLUB and SLAB memory allocators.
 For better bug detection and nicer reporting, enable CONFIG_STACKTRACE.
 
 To disable instrumentation for specific files or directories, add a line

@@ -43,85 +52,80 @@ similar to the following to the respective kernel Makefile:
 Error reports
 ~~~~~~~~~~~~~
 
-A typical out of bounds access report looks like this::
+A typical out-of-bounds access classic KASAN report looks like this::
 
     ==================================================================
-    BUG: AddressSanitizer: out of bounds access in kmalloc_oob_right+0x65/0x75 [test_kasan] at addr ffff8800693bc5d3
-    Write of size 1 by task modprobe/1689
-    =============================================================================
-    BUG kmalloc-128 (Not tainted): kasan error
-    -----------------------------------------------------------------------------
-
-    Disabling lock debugging due to kernel taint
-    INFO: Allocated in kmalloc_oob_right+0x3d/0x75 [test_kasan] age=0 cpu=0 pid=1689
-     __slab_alloc+0x4b4/0x4f0
-     kmem_cache_alloc_trace+0x10b/0x190
-     kmalloc_oob_right+0x3d/0x75 [test_kasan]
-     init_module+0x9/0x47 [test_kasan]
-     do_one_initcall+0x99/0x200
-     load_module+0x2cb3/0x3b20
-     SyS_finit_module+0x76/0x80
-     system_call_fastpath+0x12/0x17
-    INFO: Slab 0xffffea0001a4ef00 objects=17 used=7 fp=0xffff8800693bd728 flags=0x100000000004080
-    INFO: Object 0xffff8800693bc558 @offset=1368 fp=0xffff8800693bc720
-
-    Bytes b4 ffff8800693bc548: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a  ........ZZZZZZZZ
-    Object ffff8800693bc558: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc568: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc578: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc588: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc598: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5a8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5b8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5c8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5  kkkkkkkkkkkkkkk.
-    Redzone ffff8800693bc5d8: cc cc cc cc cc cc cc cc                          ........
-    Padding ffff8800693bc718: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ
-    CPU: 0 PID: 1689 Comm: modprobe Tainted: G    B          3.18.0-rc1-mm1+ #98
-    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
-     ffff8800693bc000 0000000000000000 ffff8800693bc558 ffff88006923bb78
-     ffffffff81cc68ae 00000000000000f3 ffff88006d407600 ffff88006923bba8
-     ffffffff811fd848 ffff88006d407600 ffffea0001a4ef00 ffff8800693bc558
+    BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xa8/0xbc [test_kasan]
+    Write of size 1 at addr ffff8800696f3d3b by task insmod/2734
+    
+    CPU: 0 PID: 2734 Comm: insmod Not tainted 4.15.0+ #98
+    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
     Call Trace:
-     [<ffffffff81cc68ae>] dump_stack+0x46/0x58
-     [<ffffffff811fd848>] print_trailer+0xf8/0x160
-     [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
-     [<ffffffff811ff0f5>] object_err+0x35/0x40
-     [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffff8120b9fa>] kasan_report_error+0x38a/0x3f0
-     [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
-     [<ffffffff8120b344>] ? kasan_unpoison_shadow+0x14/0x40
-     [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
-     [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
-     [<ffffffff8120a995>] __asan_store1+0x75/0xb0
-     [<ffffffffa0002601>] ? kmem_cache_oob+0x1d/0xc3 [test_kasan]
-     [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffffa0002065>] kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffffa00026b0>] init_module+0x9/0x47 [test_kasan]
-     [<ffffffff810002d9>] do_one_initcall+0x99/0x200
-     [<ffffffff811e4e5c>] ? __vunmap+0xec/0x160
-     [<ffffffff81114f63>] load_module+0x2cb3/0x3b20
-     [<ffffffff8110fd70>] ? m_show+0x240/0x240
-     [<ffffffff81115f06>] SyS_finit_module+0x76/0x80
-     [<ffffffff81cd3129>] system_call_fastpath+0x12/0x17
+     __dump_stack lib/dump_stack.c:17
+     dump_stack+0x83/0xbc lib/dump_stack.c:53
+     print_address_description+0x73/0x280 mm/kasan/report.c:254
+     kasan_report_error mm/kasan/report.c:352
+     kasan_report+0x10e/0x220 mm/kasan/report.c:410
+     __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:505
+     kmalloc_oob_right+0xa8/0xbc [test_kasan] lib/test_kasan.c:42
+     kmalloc_tests_init+0x16/0x769 [test_kasan]
+     do_one_initcall+0x9e/0x240 init/main.c:832
+     do_init_module+0x1b6/0x542 kernel/module.c:3462
+     load_module+0x6042/0x9030 kernel/module.c:3786
+     SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
+     SyS_init_module+0x9/0x10 kernel/module.c:3841
+     do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
+     entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
+    RIP: 0033:0x7fdd79df99da
+    RSP: 002b:00007fff2229bdf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000af
+    RAX: ffffffffffffffda RBX: 000055c408121190 RCX: 00007fdd79df99da
+    RDX: 00007fdd7a0b8f88 RSI: 0000000000055670 RDI: 00007fdd7a47e000
+    RBP: 000055c4081200b0 R08: 0000000000000003 R09: 0000000000000000
+    R10: 00007fdd79df5d0a R11: 0000000000000202 R12: 00007fdd7a0b8f88
+    R13: 000055c408120090 R14: 0000000000000000 R15: 0000000000000000
+    
+    Allocated by task 2734:
+     save_stack+0x43/0xd0 mm/kasan/common.c:176
+     set_track+0x20/0x30 mm/kasan/common.c:188
+     kasan_kmalloc+0x9a/0xc0 mm/kasan/kasan.c:372
+     kmem_cache_alloc_trace+0xcd/0x1a0 mm/slub.c:2761
+     kmalloc ./include/linux/slab.h:512
+     kmalloc_oob_right+0x56/0xbc [test_kasan] lib/test_kasan.c:36
+     kmalloc_tests_init+0x16/0x769 [test_kasan]
+     do_one_initcall+0x9e/0x240 init/main.c:832
+     do_init_module+0x1b6/0x542 kernel/module.c:3462
+     load_module+0x6042/0x9030 kernel/module.c:3786
+     SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
+     SyS_init_module+0x9/0x10 kernel/module.c:3841
+     do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
+     entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
+    
+    The buggy address belongs to the object at ffff8800696f3cc0
+     which belongs to the cache kmalloc-128 of size 128
+    The buggy address is located 123 bytes inside of
+     128-byte region [ffff8800696f3cc0, ffff8800696f3d40)
+    The buggy address belongs to the page:
+    page:ffffea0001a5bcc0 count:1 mapcount:0 mapping:          (null) index:0x0
+    flags: 0x100000000000100(slab)
+    raw: 0100000000000100 0000000000000000 0000000000000000 0000000180150015
+    raw: ffffea0001a8ce40 0000000300000003 ffff88006d001640 0000000000000000
+    page dumped because: kasan: bad access detected
+    
     Memory state around the buggy address:
-     ffff8800693bc300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc380: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
-     ffff8800693bc400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc500: fc fc fc fc fc fc fc fc fc fc fc 00 00 00 00 00
-    >ffff8800693bc580: 00 00 00 00 00 00 00 00 00 00 03 fc fc fc fc fc
-                                                 ^
-     ffff8800693bc600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc700: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
-     ffff8800693bc780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
-     ffff8800693bc800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
+     ffff8800696f3c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
+     ffff8800696f3c80: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
+    >ffff8800696f3d00: 00 00 00 00 00 00 00 03 fc fc fc fc fc fc fc fc
+                                            ^
+     ffff8800696f3d80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc
+     ffff8800696f3e00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
     ==================================================================
 
-The header of the report discribe what kind of bug happened and what kind of
-access caused it. It's followed by the description of the accessed slub object
-(see 'SLUB Debug output' section in Documentation/vm/slub.txt for details) and
-the description of the accessed memory page.
+The header of the report provides a short summary of what kind of bug happened
+and what kind of access caused it. It's followed by a stack trace of the bad
+access, a stack trace of where the accessed memory was allocated (in case bad
+access happens on a slab object), and a stack trace of where the object was
+freed (in case of a use-after-free bug report). Next comes a description of
+the accessed slab object and information about the accessed memory page.
 
 In the last section the report shows memory state around the accessed address.
 Reading this part requires some understanding of how KASAN works.

@@ -138,18 +142,24 @@ inaccessible memory like redzones or freed memory (see mm/kasan/kasan.h).
 In the report above the arrows point to the shadow byte 03, which means that
 the accessed address is partially accessible.
 
+For KHWASAN this last report section shows the memory tags around the accessed
+address (see Implementation details section).
+
 
 Implementation details
 ----------------------
 
+Classic KASAN
+~~~~~~~~~~~~~
+
 From a high level, our approach to memory error detection is similar to that
 of kmemcheck: use shadow memory to record whether each byte of memory is safe
-to access, and use compile-time instrumentation to check shadow memory on each
-memory access.
+to access, and use compile-time instrumentation to insert checks of shadow
+memory on each memory access.
 
-AddressSanitizer dedicates 1/8 of kernel memory to its shadow memory
-(e.g. 16TB to cover 128TB on x86_64) and uses direct mapping with a scale and
-offset to translate a memory address to its corresponding shadow address.
+Classic KASAN dedicates 1/8th of kernel memory to its shadow memory (e.g. 16TB
+to cover 128TB on x86_64) and uses direct mapping with a scale and offset to
+translate a memory address to its corresponding shadow address.
 
 Here is the function which translates an address to its corresponding shadow
 address::

@@ -162,12 +172,34 @@ address::
 
 where ``KASAN_SHADOW_SCALE_SHIFT = 3``.
 
-Compile-time instrumentation used for checking memory accesses. Compiler inserts
-function calls (__asan_load*(addr), __asan_store*(addr)) before each memory
-access of size 1, 2, 4, 8 or 16. These functions check whether memory access is
-valid or not by checking corresponding shadow memory.
+Compile-time instrumentation is used to insert memory accesses checks. Compiler
+inserts function calls (__asan_load*(addr), __asan_store*(addr)) before each
+memory access of size 1, 2, 4, 8 or 16. These functions check whether memory
+access is valid or not by checking corresponding shadow memory.
 
 GCC 5.0 has possibility to perform inline instrumentation. Instead of making
 function calls GCC directly inserts the code to check the shadow memory.
 This option significantly enlarges kernel but it gives x1.1-x2 performance
 boost over outline instrumented kernel.
+
+KHWASAN
+~~~~~~~
+
+KHWASAN uses the Top Byte Ignore (TBI) feature of modern arm64 CPUs to store
+a pointer tag in the top byte of kernel pointers. KHWASAN also uses shadow
+memory to store memory tags associated with each 16-byte memory cell (therefore
+it dedicates 1/16th of the kernel memory for shadow memory).
+
+On each memory allocation KHWASAN generates a random tag, tags allocated memory
+with this tag, and embeds this tag into the returned pointer. KHWASAN uses
+compile-time instrumentation to insert checks before each memory access. These
+checks make sure that tag of the memory that is being accessed is equal to tag
+ofthe pointer that is used to access this memory. In case of a tag mismatch
+KHWASAN prints a bug report.
+
+KHWASAN also has two instrumentation modes (outline, that emits callbacks to
+check memory accesses; and inline, that performs the shadow memory checks
+inline). With outline instrumentation mode, a bug report is simply printed
+from the function that performs the access check. With inline instrumentation
+a brk instruction is emitted by the compiler, and a dedicated brk handler is
+used to print KHWASAN reports.

Signature · 1 line

2.17.0.484.g0c8726318c-goog

Randy Dunlap

reviewer

2018-05-26 03:14 UTC #16 lore raw

Re: [RFC PATCH v3 15/15] khwasan: update kasan documentation

Quoted 3 lines · Andrey Konovalov

This patch updates KASAN documentation to reflect the addition of KHWASAN.
Signed-off-by Andrey Konovalov <[email protected]>

Hi,
Just a few corrections below...

Quoted 32 lines

---
 Documentation/dev-tools/kasan.rst | 212 +++++++++++++++++-------------
 1 file changed, 122 insertions(+), 90 deletions(-)

Documentation/dev-tools/kasan.rst +11 -4

index f7a18f274357..bd7859538b73 100644
@@ -8,11 +8,18 @@ KernelAddressSANitizer (KASAN) is a dynamic memory error detector. It provides
 a fast and comprehensive solution for finding use-after-free and out-of-bounds
 bugs.
 
-KASAN uses compile-time instrumentation for checking every memory access,
-therefore you will need a GCC version 4.9.2 or later. GCC 5.0 or later is
-required for detection of out-of-bounds accesses to stack or global variables.
+KASAN has two modes: classic KASAN (a classic version, similar to user space
+ASan) and KHWASAN (a version based on memory tagging, similar to user space
+HWASan).
 
-Currently KASAN is supported only for the x86_64 and arm64 architectures.
+KASAN uses compile-time instrumentation to insert validity checks before every
+memory access, and therefore requires a compiler version that supports that.
+For classic KASAN you need GCC version 4.9.2 or later. GCC 5.0 or later is
+required for detection of out-of-bounds accesses on stack and global variables.
+TODO: compiler requirements for KHWASAN
+
+Currently classic KASAN is supported for the x86_64, arm64 and xtensa
+architectures, and KHWASAN is supported only for arm64.
 
 Usage
 -----

Documentation/dev-tools/kasan.rst To enable KASAN configure kernel with:: · line 34

Quoted 10 lines

Documentation/dev-tools/kasan.rst +4 -3

@@ -21,12 +28,14 @@ To enable KASAN configure kernel with::
 
 	  CONFIG_KASAN = y
 
-and choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and
-inline are compiler instrumentation types. The former produces smaller binary
-the latter is 1.1 - 2 times faster. Inline instrumentation requires a GCC
+and choose between CONFIG_KASAN_GENERIC (to enable classic KASAN) and
+CONFIG_KASAN_HW (to enabled KHWASAN). You also need to choose choose between
+CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and inline are compiler
+instrumentation types. The former produces smaller binary the latter is

smaller binary while the latter is

Quoted 193 lines

Documentation/dev-tools/kasan.rst +81 ~~-79~~

+1.1 - 2 times faster. For classic KASAN inline instrumentation requires GCC
 version 5.0 or later.
 
-KASAN works with both SLUB and SLAB memory allocators.
+Both KASAN modes work with both SLUB and SLAB memory allocators.
 For better bug detection and nicer reporting, enable CONFIG_STACKTRACE.
 
 To disable instrumentation for specific files or directories, add a line

@@ -43,85 +52,80 @@ similar to the following to the respective kernel Makefile:
 Error reports
 ~~~~~~~~~~~~~
 
-A typical out of bounds access report looks like this::
+A typical out-of-bounds access classic KASAN report looks like this::
 
     ==================================================================
-    BUG: AddressSanitizer: out of bounds access in kmalloc_oob_right+0x65/0x75 [test_kasan] at addr ffff8800693bc5d3
-    Write of size 1 by task modprobe/1689
-    =============================================================================
-    BUG kmalloc-128 (Not tainted): kasan error
-    -----------------------------------------------------------------------------
-
-    Disabling lock debugging due to kernel taint
-    INFO: Allocated in kmalloc_oob_right+0x3d/0x75 [test_kasan] age=0 cpu=0 pid=1689
-     __slab_alloc+0x4b4/0x4f0
-     kmem_cache_alloc_trace+0x10b/0x190
-     kmalloc_oob_right+0x3d/0x75 [test_kasan]
-     init_module+0x9/0x47 [test_kasan]
-     do_one_initcall+0x99/0x200
-     load_module+0x2cb3/0x3b20
-     SyS_finit_module+0x76/0x80
-     system_call_fastpath+0x12/0x17
-    INFO: Slab 0xffffea0001a4ef00 objects=17 used=7 fp=0xffff8800693bd728 flags=0x100000000004080
-    INFO: Object 0xffff8800693bc558 @offset=1368 fp=0xffff8800693bc720
-
-    Bytes b4 ffff8800693bc548: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a  ........ZZZZZZZZ
-    Object ffff8800693bc558: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc568: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc578: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc588: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc598: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5a8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5b8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5c8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5  kkkkkkkkkkkkkkk.
-    Redzone ffff8800693bc5d8: cc cc cc cc cc cc cc cc                          ........
-    Padding ffff8800693bc718: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ
-    CPU: 0 PID: 1689 Comm: modprobe Tainted: G    B          3.18.0-rc1-mm1+ #98
-    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
-     ffff8800693bc000 0000000000000000 ffff8800693bc558 ffff88006923bb78
-     ffffffff81cc68ae 00000000000000f3 ffff88006d407600 ffff88006923bba8
-     ffffffff811fd848 ffff88006d407600 ffffea0001a4ef00 ffff8800693bc558
+    BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xa8/0xbc [test_kasan]
+    Write of size 1 at addr ffff8800696f3d3b by task insmod/2734
+    
+    CPU: 0 PID: 2734 Comm: insmod Not tainted 4.15.0+ #98
+    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
     Call Trace:
-     [<ffffffff81cc68ae>] dump_stack+0x46/0x58
-     [<ffffffff811fd848>] print_trailer+0xf8/0x160
-     [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
-     [<ffffffff811ff0f5>] object_err+0x35/0x40
-     [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffff8120b9fa>] kasan_report_error+0x38a/0x3f0
-     [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
-     [<ffffffff8120b344>] ? kasan_unpoison_shadow+0x14/0x40
-     [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
-     [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
-     [<ffffffff8120a995>] __asan_store1+0x75/0xb0
-     [<ffffffffa0002601>] ? kmem_cache_oob+0x1d/0xc3 [test_kasan]
-     [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffffa0002065>] kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffffa00026b0>] init_module+0x9/0x47 [test_kasan]
-     [<ffffffff810002d9>] do_one_initcall+0x99/0x200
-     [<ffffffff811e4e5c>] ? __vunmap+0xec/0x160
-     [<ffffffff81114f63>] load_module+0x2cb3/0x3b20
-     [<ffffffff8110fd70>] ? m_show+0x240/0x240
-     [<ffffffff81115f06>] SyS_finit_module+0x76/0x80
-     [<ffffffff81cd3129>] system_call_fastpath+0x12/0x17
+     __dump_stack lib/dump_stack.c:17
+     dump_stack+0x83/0xbc lib/dump_stack.c:53
+     print_address_description+0x73/0x280 mm/kasan/report.c:254
+     kasan_report_error mm/kasan/report.c:352
+     kasan_report+0x10e/0x220 mm/kasan/report.c:410
+     __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:505
+     kmalloc_oob_right+0xa8/0xbc [test_kasan] lib/test_kasan.c:42
+     kmalloc_tests_init+0x16/0x769 [test_kasan]
+     do_one_initcall+0x9e/0x240 init/main.c:832
+     do_init_module+0x1b6/0x542 kernel/module.c:3462
+     load_module+0x6042/0x9030 kernel/module.c:3786
+     SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
+     SyS_init_module+0x9/0x10 kernel/module.c:3841
+     do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
+     entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
+    RIP: 0033:0x7fdd79df99da
+    RSP: 002b:00007fff2229bdf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000af
+    RAX: ffffffffffffffda RBX: 000055c408121190 RCX: 00007fdd79df99da
+    RDX: 00007fdd7a0b8f88 RSI: 0000000000055670 RDI: 00007fdd7a47e000
+    RBP: 000055c4081200b0 R08: 0000000000000003 R09: 0000000000000000
+    R10: 00007fdd79df5d0a R11: 0000000000000202 R12: 00007fdd7a0b8f88
+    R13: 000055c408120090 R14: 0000000000000000 R15: 0000000000000000
+    
+    Allocated by task 2734:
+     save_stack+0x43/0xd0 mm/kasan/common.c:176
+     set_track+0x20/0x30 mm/kasan/common.c:188
+     kasan_kmalloc+0x9a/0xc0 mm/kasan/kasan.c:372
+     kmem_cache_alloc_trace+0xcd/0x1a0 mm/slub.c:2761
+     kmalloc ./include/linux/slab.h:512
+     kmalloc_oob_right+0x56/0xbc [test_kasan] lib/test_kasan.c:36
+     kmalloc_tests_init+0x16/0x769 [test_kasan]
+     do_one_initcall+0x9e/0x240 init/main.c:832
+     do_init_module+0x1b6/0x542 kernel/module.c:3462
+     load_module+0x6042/0x9030 kernel/module.c:3786
+     SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
+     SyS_init_module+0x9/0x10 kernel/module.c:3841
+     do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
+     entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
+    
+    The buggy address belongs to the object at ffff8800696f3cc0
+     which belongs to the cache kmalloc-128 of size 128
+    The buggy address is located 123 bytes inside of
+     128-byte region [ffff8800696f3cc0, ffff8800696f3d40)
+    The buggy address belongs to the page:
+    page:ffffea0001a5bcc0 count:1 mapcount:0 mapping:          (null) index:0x0
+    flags: 0x100000000000100(slab)
+    raw: 0100000000000100 0000000000000000 0000000000000000 0000000180150015
+    raw: ffffea0001a8ce40 0000000300000003 ffff88006d001640 0000000000000000
+    page dumped because: kasan: bad access detected
+    
     Memory state around the buggy address:
-     ffff8800693bc300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc380: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
-     ffff8800693bc400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc500: fc fc fc fc fc fc fc fc fc fc fc 00 00 00 00 00
-    >ffff8800693bc580: 00 00 00 00 00 00 00 00 00 00 03 fc fc fc fc fc
-                                                 ^
-     ffff8800693bc600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc700: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
-     ffff8800693bc780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
-     ffff8800693bc800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
+     ffff8800696f3c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
+     ffff8800696f3c80: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
+    >ffff8800696f3d00: 00 00 00 00 00 00 00 03 fc fc fc fc fc fc fc fc
+                                            ^
+     ffff8800696f3d80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc
+     ffff8800696f3e00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
     ==================================================================
 
-The header of the report discribe what kind of bug happened and what kind of
-access caused it. It's followed by the description of the accessed slub object
-(see 'SLUB Debug output' section in Documentation/vm/slub.txt for details) and
-the description of the accessed memory page.
+The header of the report provides a short summary of what kind of bug happened
+and what kind of access caused it. It's followed by a stack trace of the bad
+access, a stack trace of where the accessed memory was allocated (in case bad
+access happens on a slab object), and a stack trace of where the object was
+freed (in case of a use-after-free bug report). Next comes a description of
+the accessed slab object and information about the accessed memory page.
 
 In the last section the report shows memory state around the accessed address.
 Reading this part requires some understanding of how KASAN works.

@@ -138,18 +142,24 @@ inaccessible memory like redzones or freed memory (see mm/kasan/kasan.h).
 In the report above the arrows point to the shadow byte 03, which means that
 the accessed address is partially accessible.
 
+For KHWASAN this last report section shows the memory tags around the accessed
+address (see Implementation details section).
+
 
 Implementation details
 ----------------------
 
+Classic KASAN
+~~~~~~~~~~~~~
+
 From a high level, our approach to memory error detection is similar to that
 of kmemcheck: use shadow memory to record whether each byte of memory is safe
-to access, and use compile-time instrumentation to check shadow memory on each
-memory access.
+to access, and use compile-time instrumentation to insert checks of shadow
+memory on each memory access.
 
-AddressSanitizer dedicates 1/8 of kernel memory to its shadow memory
-(e.g. 16TB to cover 128TB on x86_64) and uses direct mapping with a scale and
-offset to translate a memory address to its corresponding shadow address.
+Classic KASAN dedicates 1/8th of kernel memory to its shadow memory (e.g. 16TB
+to cover 128TB on x86_64) and uses direct mapping with a scale and offset to
+translate a memory address to its corresponding shadow address.
 
 Here is the function which translates an address to its corresponding shadow
 address::

Documentation/dev-tools/kasan.rst address:: · line 175

Quoted 8 lines

Documentation/dev-tools/kasan.rst +1 -4

@@ -162,12 +172,34 @@ address::
 
 where ``KASAN_SHADOW_SCALE_SHIFT = 3``.
 
-Compile-time instrumentation used for checking memory accesses. Compiler inserts
-function calls (__asan_load*(addr), __asan_store*(addr)) before each memory
-access of size 1, 2, 4, 8 or 16. These functions check whether memory access is
-valid or not by checking corresponding shadow memory.
+Compile-time instrumentation is used to insert memory accesses checks. Compiler

memory access checks.

Quoted 12 lines

Documentation/dev-tools/kasan.rst +7 -0

+inserts function calls (__asan_load*(addr), __asan_store*(addr)) before each
+memory access of size 1, 2, 4, 8 or 16. These functions check whether memory
+access is valid or not by checking corresponding shadow memory.
 
 GCC 5.0 has possibility to perform inline instrumentation. Instead of making
 function calls GCC directly inserts the code to check the shadow memory.
 This option significantly enlarges kernel but it gives x1.1-x2 performance
 boost over outline instrumented kernel.
+
+KHWASAN
+~~~~~~~
+

Documentation/dev-tools/kasan.rst address:: · line 197

Quoted 10 lines

Documentation/dev-tools/kasan.rst +10 -0

+KHWASAN uses the Top Byte Ignore (TBI) feature of modern arm64 CPUs to store
+a pointer tag in the top byte of kernel pointers. KHWASAN also uses shadow
+memory to store memory tags associated with each 16-byte memory cell (therefore
+it dedicates 1/16th of the kernel memory for shadow memory).
+
+On each memory allocation KHWASAN generates a random tag, tags allocated memory
+with this tag, and embeds this tag into the returned pointer. KHWASAN uses
+compile-time instrumentation to insert checks before each memory access. These
+checks make sure that tag of the memory that is being accessed is equal to tag
+ofthe pointer that is used to access this memory. In case of a tag mismatch

of the

Documentation/dev-tools/kasan.rst address:: · line 205

Quoted 9 lines

Documentation/dev-tools/kasan.rst +8 -0

+KHWASAN prints a bug report.
+
+KHWASAN also has two instrumentation modes (outline, that emits callbacks to
+check memory accesses; and inline, that performs the shadow memory checks
+inline). With outline instrumentation mode, a bug report is simply printed
+from the function that performs the access check. With inline instrumentation
+a brk instruction is emitted by the compiler, and a dedicated brk handler is
+used to print KHWASAN reports.

thanks,

Signature · 1 line

~Randy

Andrey Konovalov

author

2018-05-28 12:11 UTC #17 lore raw

Re: [RFC PATCH v3 15/15] khwasan: update kasan documentation

Quoted 282 lines · Randy Dunlap

Quoted 3 lines · Andrey Konovalov

This patch updates KASAN documentation to reflect the addition of KHWASAN.
Signed-off-by Andrey Konovalov <[email protected]>

Hi,
Just a few corrections below...

Quoted 32 lines

---
 Documentation/dev-tools/kasan.rst | 212 +++++++++++++++++-------------
 1 file changed, 122 insertions(+), 90 deletions(-)

Documentation/dev-tools/kasan.rst +11 -4

index f7a18f274357..bd7859538b73 100644
@@ -8,11 +8,18 @@ KernelAddressSANitizer (KASAN) is a dynamic memory error detector. It provides
 a fast and comprehensive solution for finding use-after-free and out-of-bounds
 bugs.
 
-KASAN uses compile-time instrumentation for checking every memory access,
-therefore you will need a GCC version 4.9.2 or later. GCC 5.0 or later is
-required for detection of out-of-bounds accesses to stack or global variables.
+KASAN has two modes: classic KASAN (a classic version, similar to user space
+ASan) and KHWASAN (a version based on memory tagging, similar to user space
+HWASan).
 
-Currently KASAN is supported only for the x86_64 and arm64 architectures.
+KASAN uses compile-time instrumentation to insert validity checks before every
+memory access, and therefore requires a compiler version that supports that.
+For classic KASAN you need GCC version 4.9.2 or later. GCC 5.0 or later is
+required for detection of out-of-bounds accesses on stack and global variables.
+TODO: compiler requirements for KHWASAN
+
+Currently classic KASAN is supported for the x86_64, arm64 and xtensa
+architectures, and KHWASAN is supported only for arm64.
 
 Usage
 -----

Documentation/dev-tools/kasan.rst To enable KASAN configure kernel with:: · line 34

Quoted 10 lines

Documentation/dev-tools/kasan.rst +4 -3

@@ -21,12 +28,14 @@ To enable KASAN configure kernel with::
 
        CONFIG_KASAN = y
 
-and choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and
-inline are compiler instrumentation types. The former produces smaller binary
-the latter is 1.1 - 2 times faster. Inline instrumentation requires a GCC
+and choose between CONFIG_KASAN_GENERIC (to enable classic KASAN) and
+CONFIG_KASAN_HW (to enabled KHWASAN). You also need to choose choose between
+CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and inline are compiler
+instrumentation types. The former produces smaller binary the latter is

smaller binary while the latter is

Quoted 193 lines

Documentation/dev-tools/kasan.rst +81 ~~-79~~

+1.1 - 2 times faster. For classic KASAN inline instrumentation requires GCC
 version 5.0 or later.
 
-KASAN works with both SLUB and SLAB memory allocators.
+Both KASAN modes work with both SLUB and SLAB memory allocators.
 For better bug detection and nicer reporting, enable CONFIG_STACKTRACE.
 
 To disable instrumentation for specific files or directories, add a line

@@ -43,85 +52,80 @@ similar to the following to the respective kernel Makefile:
 Error reports
 ~~~~~~~~~~~~~
 
-A typical out of bounds access report looks like this::
+A typical out-of-bounds access classic KASAN report looks like this::
 
     ==================================================================
-    BUG: AddressSanitizer: out of bounds access in kmalloc_oob_right+0x65/0x75 [test_kasan] at addr ffff8800693bc5d3
-    Write of size 1 by task modprobe/1689
-    =============================================================================
-    BUG kmalloc-128 (Not tainted): kasan error
-    -----------------------------------------------------------------------------
-
-    Disabling lock debugging due to kernel taint
-    INFO: Allocated in kmalloc_oob_right+0x3d/0x75 [test_kasan] age=0 cpu=0 pid=1689
-     __slab_alloc+0x4b4/0x4f0
-     kmem_cache_alloc_trace+0x10b/0x190
-     kmalloc_oob_right+0x3d/0x75 [test_kasan]
-     init_module+0x9/0x47 [test_kasan]
-     do_one_initcall+0x99/0x200
-     load_module+0x2cb3/0x3b20
-     SyS_finit_module+0x76/0x80
-     system_call_fastpath+0x12/0x17
-    INFO: Slab 0xffffea0001a4ef00 objects=17 used=7 fp=0xffff8800693bd728 flags=0x100000000004080
-    INFO: Object 0xffff8800693bc558 @offset=1368 fp=0xffff8800693bc720
-
-    Bytes b4 ffff8800693bc548: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a  ........ZZZZZZZZ
-    Object ffff8800693bc558: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc568: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc578: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc588: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc598: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5a8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5b8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
-    Object ffff8800693bc5c8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5  kkkkkkkkkkkkkkk.
-    Redzone ffff8800693bc5d8: cc cc cc cc cc cc cc cc                          ........
-    Padding ffff8800693bc718: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ
-    CPU: 0 PID: 1689 Comm: modprobe Tainted: G    B          3.18.0-rc1-mm1+ #98
-    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
-     ffff8800693bc000 0000000000000000 ffff8800693bc558 ffff88006923bb78
-     ffffffff81cc68ae 00000000000000f3 ffff88006d407600 ffff88006923bba8
-     ffffffff811fd848 ffff88006d407600 ffffea0001a4ef00 ffff8800693bc558
+    BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xa8/0xbc [test_kasan]
+    Write of size 1 at addr ffff8800696f3d3b by task insmod/2734
+
+    CPU: 0 PID: 2734 Comm: insmod Not tainted 4.15.0+ #98
+    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
     Call Trace:
-     [<ffffffff81cc68ae>] dump_stack+0x46/0x58
-     [<ffffffff811fd848>] print_trailer+0xf8/0x160
-     [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
-     [<ffffffff811ff0f5>] object_err+0x35/0x40
-     [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffff8120b9fa>] kasan_report_error+0x38a/0x3f0
-     [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
-     [<ffffffff8120b344>] ? kasan_unpoison_shadow+0x14/0x40
-     [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
-     [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
-     [<ffffffff8120a995>] __asan_store1+0x75/0xb0
-     [<ffffffffa0002601>] ? kmem_cache_oob+0x1d/0xc3 [test_kasan]
-     [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffffa0002065>] kmalloc_oob_right+0x65/0x75 [test_kasan]
-     [<ffffffffa00026b0>] init_module+0x9/0x47 [test_kasan]
-     [<ffffffff810002d9>] do_one_initcall+0x99/0x200
-     [<ffffffff811e4e5c>] ? __vunmap+0xec/0x160
-     [<ffffffff81114f63>] load_module+0x2cb3/0x3b20
-     [<ffffffff8110fd70>] ? m_show+0x240/0x240
-     [<ffffffff81115f06>] SyS_finit_module+0x76/0x80
-     [<ffffffff81cd3129>] system_call_fastpath+0x12/0x17
+     __dump_stack lib/dump_stack.c:17
+     dump_stack+0x83/0xbc lib/dump_stack.c:53
+     print_address_description+0x73/0x280 mm/kasan/report.c:254
+     kasan_report_error mm/kasan/report.c:352
+     kasan_report+0x10e/0x220 mm/kasan/report.c:410
+     __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:505
+     kmalloc_oob_right+0xa8/0xbc [test_kasan] lib/test_kasan.c:42
+     kmalloc_tests_init+0x16/0x769 [test_kasan]
+     do_one_initcall+0x9e/0x240 init/main.c:832
+     do_init_module+0x1b6/0x542 kernel/module.c:3462
+     load_module+0x6042/0x9030 kernel/module.c:3786
+     SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
+     SyS_init_module+0x9/0x10 kernel/module.c:3841
+     do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
+     entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
+    RIP: 0033:0x7fdd79df99da
+    RSP: 002b:00007fff2229bdf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000af
+    RAX: ffffffffffffffda RBX: 000055c408121190 RCX: 00007fdd79df99da
+    RDX: 00007fdd7a0b8f88 RSI: 0000000000055670 RDI: 00007fdd7a47e000
+    RBP: 000055c4081200b0 R08: 0000000000000003 R09: 0000000000000000
+    R10: 00007fdd79df5d0a R11: 0000000000000202 R12: 00007fdd7a0b8f88
+    R13: 000055c408120090 R14: 0000000000000000 R15: 0000000000000000
+
+    Allocated by task 2734:
+     save_stack+0x43/0xd0 mm/kasan/common.c:176
+     set_track+0x20/0x30 mm/kasan/common.c:188
+     kasan_kmalloc+0x9a/0xc0 mm/kasan/kasan.c:372
+     kmem_cache_alloc_trace+0xcd/0x1a0 mm/slub.c:2761
+     kmalloc ./include/linux/slab.h:512
+     kmalloc_oob_right+0x56/0xbc [test_kasan] lib/test_kasan.c:36
+     kmalloc_tests_init+0x16/0x769 [test_kasan]
+     do_one_initcall+0x9e/0x240 init/main.c:832
+     do_init_module+0x1b6/0x542 kernel/module.c:3462
+     load_module+0x6042/0x9030 kernel/module.c:3786
+     SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
+     SyS_init_module+0x9/0x10 kernel/module.c:3841
+     do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
+     entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
+
+    The buggy address belongs to the object at ffff8800696f3cc0
+     which belongs to the cache kmalloc-128 of size 128
+    The buggy address is located 123 bytes inside of
+     128-byte region [ffff8800696f3cc0, ffff8800696f3d40)
+    The buggy address belongs to the page:
+    page:ffffea0001a5bcc0 count:1 mapcount:0 mapping:          (null) index:0x0
+    flags: 0x100000000000100(slab)
+    raw: 0100000000000100 0000000000000000 0000000000000000 0000000180150015
+    raw: ffffea0001a8ce40 0000000300000003 ffff88006d001640 0000000000000000
+    page dumped because: kasan: bad access detected
+
     Memory state around the buggy address:
-     ffff8800693bc300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc380: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
-     ffff8800693bc400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc500: fc fc fc fc fc fc fc fc fc fc fc 00 00 00 00 00
-    >ffff8800693bc580: 00 00 00 00 00 00 00 00 00 00 03 fc fc fc fc fc
-                                                 ^
-     ffff8800693bc600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
-     ffff8800693bc700: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
-     ffff8800693bc780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
-     ffff8800693bc800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
+     ffff8800696f3c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
+     ffff8800696f3c80: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
+    >ffff8800696f3d00: 00 00 00 00 00 00 00 03 fc fc fc fc fc fc fc fc
+                                            ^
+     ffff8800696f3d80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc
+     ffff8800696f3e00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
     ==================================================================
 
-The header of the report discribe what kind of bug happened and what kind of
-access caused it. It's followed by the description of the accessed slub object
-(see 'SLUB Debug output' section in Documentation/vm/slub.txt for details) and
-the description of the accessed memory page.
+The header of the report provides a short summary of what kind of bug happened
+and what kind of access caused it. It's followed by a stack trace of the bad
+access, a stack trace of where the accessed memory was allocated (in case bad
+access happens on a slab object), and a stack trace of where the object was
+freed (in case of a use-after-free bug report). Next comes a description of
+the accessed slab object and information about the accessed memory page.
 
 In the last section the report shows memory state around the accessed address.
 Reading this part requires some understanding of how KASAN works.

@@ -138,18 +142,24 @@ inaccessible memory like redzones or freed memory (see mm/kasan/kasan.h).
 In the report above the arrows point to the shadow byte 03, which means that
 the accessed address is partially accessible.
 
+For KHWASAN this last report section shows the memory tags around the accessed
+address (see Implementation details section).
+
 
 Implementation details
 ----------------------
 
+Classic KASAN
+~~~~~~~~~~~~~
+
 From a high level, our approach to memory error detection is similar to that
 of kmemcheck: use shadow memory to record whether each byte of memory is safe
-to access, and use compile-time instrumentation to check shadow memory on each
-memory access.
+to access, and use compile-time instrumentation to insert checks of shadow
+memory on each memory access.
 
-AddressSanitizer dedicates 1/8 of kernel memory to its shadow memory
-(e.g. 16TB to cover 128TB on x86_64) and uses direct mapping with a scale and
-offset to translate a memory address to its corresponding shadow address.
+Classic KASAN dedicates 1/8th of kernel memory to its shadow memory (e.g. 16TB
+to cover 128TB on x86_64) and uses direct mapping with a scale and offset to
+translate a memory address to its corresponding shadow address.
 
 Here is the function which translates an address to its corresponding shadow
 address::

Documentation/dev-tools/kasan.rst address:: · line 175

Quoted 8 lines

Documentation/dev-tools/kasan.rst +1 -4

@@ -162,12 +172,34 @@ address::
 
 where ``KASAN_SHADOW_SCALE_SHIFT = 3``.
 
-Compile-time instrumentation used for checking memory accesses. Compiler inserts
-function calls (__asan_load*(addr), __asan_store*(addr)) before each memory
-access of size 1, 2, 4, 8 or 16. These functions check whether memory access is
-valid or not by checking corresponding shadow memory.
+Compile-time instrumentation is used to insert memory accesses checks. Compiler

memory access checks.

Quoted 12 lines

Documentation/dev-tools/kasan.rst +7 -0

+inserts function calls (__asan_load*(addr), __asan_store*(addr)) before each
+memory access of size 1, 2, 4, 8 or 16. These functions check whether memory
+access is valid or not by checking corresponding shadow memory.
 
 GCC 5.0 has possibility to perform inline instrumentation. Instead of making
 function calls GCC directly inserts the code to check the shadow memory.
 This option significantly enlarges kernel but it gives x1.1-x2 performance
 boost over outline instrumented kernel.
+
+KHWASAN
+~~~~~~~
+

Documentation/dev-tools/kasan.rst address:: · line 197

Quoted 10 lines

Documentation/dev-tools/kasan.rst +10 -0

+KHWASAN uses the Top Byte Ignore (TBI) feature of modern arm64 CPUs to store
+a pointer tag in the top byte of kernel pointers. KHWASAN also uses shadow
+memory to store memory tags associated with each 16-byte memory cell (therefore
+it dedicates 1/16th of the kernel memory for shadow memory).
+
+On each memory allocation KHWASAN generates a random tag, tags allocated memory
+with this tag, and embeds this tag into the returned pointer. KHWASAN uses
+compile-time instrumentation to insert checks before each memory access. These
+checks make sure that tag of the memory that is being accessed is equal to tag
+ofthe pointer that is used to access this memory. In case of a tag mismatch

of the

Quoted 13 lines

Documentation/dev-tools/kasan.rst address:: · line 205

Quoted 9 lines

Documentation/dev-tools/kasan.rst +8 -0

+KHWASAN prints a bug report.
+
+KHWASAN also has two instrumentation modes (outline, that emits callbacks to
+check memory accesses; and inline, that performs the shadow memory checks
+inline). With outline instrumentation mode, a bug report is simply printed
+from the function that performs the access check. With inline instrumentation
+a brk instruction is emitted by the compiler, and a dedicated brk handler is
+used to print KHWASAN reports.

thanks,
--
~Randy

Hi Randy,

Will fix all in v3.

Thanks!