khwasan: kernel hardware assisted address sanitizer

PATCH Superseded Andrey Konovalov 2 participants 20 messages May 25, 2018 – Jun 4, 2018

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Andrey Konovalov

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2018-05-25 14:40 UTC #0 lore raw

v2 cover khwasan: kernel hardware assisted address sanitizer

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).

Despite that there's a particular type of bugs that KHWASAN can detect compared to KASAN: use-after-free after the object has been allocated by someone else.

====== Benchmarks

The following numbers were collected on Odroid C2 board. Both KASAN and KHWASAN were used in inline instrumentation mode.

Boot time [1]:
* ~1.7 sec for clean kernel
* ~5.0 sec for KASAN
* ~5.0 sec for KHWASAN

Slab memory usage after boot [2]:
* ~40 kb for clean kernel
* ~105 kb + 1/8th shadow ~= 118 kb for KASAN
* ~47 kb + 1/16th shadow ~= 50 kb for KHWASAN

Network performance [3]:
* 8.33 Gbits/sec for clean kernel
* 3.17 Gbits/sec for KASAN
* 2.85 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 and will be added later.

====== Changes

Changes in v2:
- Changed kmalloc_large_node_hook to return tagged pointer instead of using an output argument.
- Fix checking whether -fsanitize=hwaddress is supported by the compiler.
- Removed duplication of -fno-builtin for KASAN and KHWASAN.
- Removed {} block for one line for_each_possible_cpu loop.
- Made set_track() static inline as it is used only in common.c.
- Moved optimal_redzone() to common.c.
- Fixed using tagged pointer for shadow calculation in kasan_unpoison_shadow().
- Restored setting cache->align in kasan_cache_create(), which was accidentally lost.
- Simplified __kasan_slab_free(), kasan_alloc_pages() and kasan_kmalloc().
- Removed tagging from kasan_kmalloc_large().
- Added page_kasan_tag_reset() to kasan_poison_slab() and removed !PageSlab() check from page_to_virt.
- Reset pointer tag in _virt_addr_is_linear.
- Set page tag for each page when multiple pages are allocated or freed.
- Added a comment as to why we ignore cma allocated pages.

Changes in v1:
- Rebased onto 4.17-rc4.
- Updated benchmarking stats.
- Documented compiler version requirements, memory usage and slowdown.
- Dropped kvm patches, as clang + arm64 + kvm is completely broken [1].

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 (ita??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 [1]).

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.

[1] https://lkml.org/lkml/2018/4/19/775

Andrey Konovalov (16):
khwasan, mm: change kasan hooks signatures
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 and
_virt_addr_is_linear
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      | 213 +++++----
 arch/arm64/Kconfig                     |   1 +
 arch/arm64/Makefile                    |   2 +-
 arch/arm64/include/asm/brk-imm.h       |   2 +
 arch/arm64/include/asm/memory.h        |  41 +-
 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                  |  84 +++-
 include/linux/mm.h                     |  29 ++
 include/linux/page-flags-layout.h      |  10 +
 lib/Kconfig.kasan                      |  76 +++-
 mm/cma.c                               |  11 +
 mm/kasan/Makefile                      |   9 +-
 mm/kasan/common.c                      | 598 +++++++++++++++++++++++++
 mm/kasan/kasan.c                       | 503 +--------------------
 mm/kasan/kasan.h                       |  85 +++-
 mm/kasan/kasan_report.c                | 155 +++++++
 mm/kasan/khwasan.c                     | 162 +++++++
 mm/kasan/khwasan_report.c              |  60 +++
 mm/kasan/report.c                      | 271 +++--------
 mm/page_alloc.c                        |   1 +
 mm/slab.c                              |  12 +-
 mm/slab.h                              |   2 +-
 mm/slab_common.c                       |   6 +-
 mm/slub.c                              |  17 +-
 scripts/Makefile.kasan                 |  27 +-
 32 files changed, 1630 insertions(+), 858 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 · 1 line

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:40 UTC #1 lore raw

PATCH v2 1/16 khwasan, mm: change kasan hooks signatures

KHWASAN will change the value of the top byte of pointers returned from the kernel allocation functions (such as kmalloc). This patch updates KASAN hooks signatures and their usage in SLAB and SLUB code to reflect that.

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

---
 include/linux/kasan.h | 34 +++++++++++++++++++++++-----------
 mm/kasan/kasan.c      | 24 ++++++++++++++----------
 mm/slab.c             | 12 ++++++------
 mm/slab.h             |  2 +-
 mm/slab_common.c      |  4 ++--
 mm/slub.c             | 15 +++++++--------
 6 files changed, 53 insertions(+), 38 deletions(-)

include/linux/kasan.h +23 ~~-11~~

index de784fd11d12..cbdc54543803 100644
@@ -53,14 +53,14 @@ void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
 void kasan_poison_object_data(struct kmem_cache *cache, void *object);
 void kasan_init_slab_obj(struct kmem_cache *cache, const void *object);
 
-void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags);
+void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags);
 void kasan_kfree_large(void *ptr, unsigned long ip);
 void kasan_poison_kfree(void *ptr, unsigned long ip);
-void kasan_kmalloc(struct kmem_cache *s, const void *object, size_t size,
+void *kasan_kmalloc(struct kmem_cache *s, const void *object, size_t size,
 		  gfp_t flags);
-void kasan_krealloc(const void *object, size_t new_size, gfp_t flags);
+void *kasan_krealloc(const void *object, size_t new_size, gfp_t flags);
 
-void kasan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags);
+void *kasan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags);
 bool kasan_slab_free(struct kmem_cache *s, void *object, unsigned long ip);
 
 struct kasan_cache {

@@ -105,16 +105,28 @@ static inline void kasan_poison_object_data(struct kmem_cache *cache,
 static inline void kasan_init_slab_obj(struct kmem_cache *cache,
 				const void *object) {}
 
-static inline void kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags) {}
+static inline void *kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags)
+{
+	return ptr;
+}
 static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
 static inline void kasan_poison_kfree(void *ptr, unsigned long ip) {}
-static inline void kasan_kmalloc(struct kmem_cache *s, const void *object,
-				size_t size, gfp_t flags) {}
-static inline void kasan_krealloc(const void *object, size_t new_size,
-				 gfp_t flags) {}
+static inline void *kasan_kmalloc(struct kmem_cache *s, const void *object,
+				size_t size, gfp_t flags)
+{
+	return (void *)object;
+}
+static inline void *kasan_krealloc(const void *object, size_t new_size,
+				 gfp_t flags)
+{
+	return (void *)object;
+}
 
-static inline void kasan_slab_alloc(struct kmem_cache *s, void *object,
-				   gfp_t flags) {}
+static inline void *kasan_slab_alloc(struct kmem_cache *s, void *object,
+				   gfp_t flags)
+{
+	return object;
+}
 static inline bool kasan_slab_free(struct kmem_cache *s, void *object,
 				   unsigned long ip)
 {

mm/kasan/kasan.c +14 ~~-10~~

index bc0e68f7dc75..2f5e52d72c2b 100644
@@ -485,9 +485,9 @@ void kasan_init_slab_obj(struct kmem_cache *cache, const void *object)
 	__memset(alloc_info, 0, sizeof(*alloc_info));
 }
 
-void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
+void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
 {
-	kasan_kmalloc(cache, object, cache->object_size, flags);
+	return kasan_kmalloc(cache, object, cache->object_size, flags);
 }
 
 static bool __kasan_slab_free(struct kmem_cache *cache, void *object,

@@ -528,7 +528,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
 	return __kasan_slab_free(cache, object, ip, true);
 }
 
-void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
+void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
 		   gfp_t flags)
 {
 	unsigned long redzone_start;

@@ -538,7 +538,7 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
 		quarantine_reduce();
 
 	if (unlikely(object == NULL))
-		return;
+		return NULL;
 
 	redzone_start = round_up((unsigned long)(object + size),
 				KASAN_SHADOW_SCALE_SIZE);

@@ -551,10 +551,12 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
 
 	if (cache->flags & SLAB_KASAN)
 		set_track(&get_alloc_info(cache, object)->alloc_track, flags);
+
+	return (void *)object;
 }
 EXPORT_SYMBOL(kasan_kmalloc);
 
-void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
+void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
 {
 	struct page *page;
 	unsigned long redzone_start;

@@ -564,7 +566,7 @@ void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
 		quarantine_reduce();
 
 	if (unlikely(ptr == NULL))
-		return;
+		return NULL;
 
 	page = virt_to_page(ptr);
 	redzone_start = round_up((unsigned long)(ptr + size),

@@ -574,21 +576,23 @@ void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
 	kasan_unpoison_shadow(ptr, size);
 	kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
 		KASAN_PAGE_REDZONE);
+
+	return (void *)ptr;
 }
 
-void kasan_krealloc(const void *object, size_t size, gfp_t flags)
+void *kasan_krealloc(const void *object, size_t size, gfp_t flags)
 {
 	struct page *page;
 
 	if (unlikely(object == ZERO_SIZE_PTR))
-		return;
+		return ZERO_SIZE_PTR;
 
 	page = virt_to_head_page(object);
 
 	if (unlikely(!PageSlab(page)))
-		kasan_kmalloc_large(object, size, flags);
+		return kasan_kmalloc_large(object, size, flags);
 	else
-		kasan_kmalloc(page->slab_cache, object, size, flags);
+		return kasan_kmalloc(page->slab_cache, object, size, flags);
 }
 
 void kasan_poison_kfree(void *ptr, unsigned long ip)

mm/slab.c +6 -6

index 2f308253c3d7..5f2aeeb18d3c 100644
@@ -3551,7 +3551,7 @@ void *kmem_cache_alloc(struct kmem_cache *cachep, gfp_t flags)
 {
 	void *ret = slab_alloc(cachep, flags, _RET_IP_);
 
-	kasan_slab_alloc(cachep, ret, flags);
+	ret = kasan_slab_alloc(cachep, ret, flags);
 	trace_kmem_cache_alloc(_RET_IP_, ret,
 			       cachep->object_size, cachep->size, flags);

@@ -3617,7 +3617,7 @@ kmem_cache_alloc_trace(struct kmem_cache *cachep, gfp_t flags, size_t size)
 
 	ret = slab_alloc(cachep, flags, _RET_IP_);
 
-	kasan_kmalloc(cachep, ret, size, flags);
+	ret = kasan_kmalloc(cachep, ret, size, flags);
 	trace_kmalloc(_RET_IP_, ret,
 		      size, cachep->size, flags);
 	return ret;

@@ -3641,7 +3641,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid)
 {
 	void *ret = slab_alloc_node(cachep, flags, nodeid, _RET_IP_);
 
-	kasan_slab_alloc(cachep, ret, flags);
+	ret = kasan_slab_alloc(cachep, ret, flags);
 	trace_kmem_cache_alloc_node(_RET_IP_, ret,
 				    cachep->object_size, cachep->size,
 				    flags, nodeid);

@@ -3660,7 +3660,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *cachep,
 
 	ret = slab_alloc_node(cachep, flags, nodeid, _RET_IP_);
 
-	kasan_kmalloc(cachep, ret, size, flags);
+	ret = kasan_kmalloc(cachep, ret, size, flags);
 	trace_kmalloc_node(_RET_IP_, ret,
 			   size, cachep->size,
 			   flags, nodeid);

@@ -3679,7 +3679,7 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
 	if (unlikely(ZERO_OR_NULL_PTR(cachep)))
 		return cachep;
 	ret = kmem_cache_alloc_node_trace(cachep, flags, node, size);
-	kasan_kmalloc(cachep, ret, size, flags);
+	ret = kasan_kmalloc(cachep, ret, size, flags);
 
 	return ret;
 }

@@ -3715,7 +3715,7 @@ static __always_inline void *__do_kmalloc(size_t size, gfp_t flags,
 		return cachep;
 	ret = slab_alloc(cachep, flags, caller);
 
-	kasan_kmalloc(cachep, ret, size, flags);
+	ret = kasan_kmalloc(cachep, ret, size, flags);
 	trace_kmalloc(caller, ret,
 		      size, cachep->size, flags);

mm/slab.h +1 -1

index 68bdf498da3b..15ef6a0d9c16 100644
@@ -441,7 +441,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s, gfp_t flags,
 
 		kmemleak_alloc_recursive(object, s->object_size, 1,
 					 s->flags, flags);
-		kasan_slab_alloc(s, object, flags);
+		p[i] = kasan_slab_alloc(s, object, flags);
 	}
 
 	if (memcg_kmem_enabled())

mm/slab_common.c +2 -2

index 98dcdc352062..0582004351c4 100644
@@ -1148,7 +1148,7 @@ void *kmalloc_order(size_t size, gfp_t flags, unsigned int order)
 	page = alloc_pages(flags, order);
 	ret = page ? page_address(page) : NULL;
 	kmemleak_alloc(ret, size, 1, flags);
-	kasan_kmalloc_large(ret, size, flags);
+	ret = kasan_kmalloc_large(ret, size, flags);
 	return ret;
 }
 EXPORT_SYMBOL(kmalloc_order);

@@ -1426,7 +1426,7 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
 		ks = ksize(p);
 
 	if (ks >= new_size) {
-		kasan_krealloc((void *)p, new_size, flags);
+		p = kasan_krealloc((void *)p, new_size, flags);
 		return (void *)p;
 	}

mm/slub.c +7 -8

index 44aa7847324a..46c5b1e481c3 100644
@@ -1351,10 +1351,10 @@ static inline void dec_slabs_node(struct kmem_cache *s, int node,
  * Hooks for other subsystems that check memory allocations. In a typical
  * production configuration these hooks all should produce no code at all.
  */
-static inline void kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags)
+static inline void *kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags)
 {
 	kmemleak_alloc(ptr, size, 1, flags);
-	kasan_kmalloc_large(ptr, size, flags);
+	return kasan_kmalloc_large(ptr, size, flags);
 }
 
 static __always_inline void kfree_hook(void *x)

@@ -2765,7 +2765,7 @@ void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
 {
 	void *ret = slab_alloc(s, gfpflags, _RET_IP_);
 	trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags);
-	kasan_kmalloc(s, ret, size, gfpflags);
+	ret = kasan_kmalloc(s, ret, size, gfpflags);
 	return ret;
 }
 EXPORT_SYMBOL(kmem_cache_alloc_trace);

@@ -2793,7 +2793,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
 	trace_kmalloc_node(_RET_IP_, ret,
 			   size, s->size, gfpflags, node);
 
-	kasan_kmalloc(s, ret, size, gfpflags);
+	ret = kasan_kmalloc(s, ret, size, gfpflags);
 	return ret;
 }
 EXPORT_SYMBOL(kmem_cache_alloc_node_trace);

@@ -3786,7 +3786,7 @@ void *__kmalloc(size_t size, gfp_t flags)
 
 	trace_kmalloc(_RET_IP_, ret, size, s->size, flags);
 
-	kasan_kmalloc(s, ret, size, flags);
+	ret = kasan_kmalloc(s, ret, size, flags);
 
 	return ret;
 }

@@ -3803,8 +3803,7 @@ static void *kmalloc_large_node(size_t size, gfp_t flags, int node)
 	if (page)
 		ptr = page_address(page);
 
-	kmalloc_large_node_hook(ptr, size, flags);
-	return ptr;
+	return kmalloc_large_node_hook(ptr, size, flags);
 }
 
 void *__kmalloc_node(size_t size, gfp_t flags, int node)

@@ -3831,7 +3830,7 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
 
 	trace_kmalloc_node(_RET_IP_, ret, size, s->size, flags, node);
 
-	kasan_kmalloc(s, ret, size, flags);
+	ret = kasan_kmalloc(s, ret, size, flags);
 
 	return ret;
 }

Signature · 1 line

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:40 UTC #2 lore raw

PATCH v2 2/16 khwasan: move common kasan and khwasan code to common.c

In reply to Andrey Konovalov

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 | 543 ++++++++++++++++++++++++++++++++++++++++++++++
 mm/kasan/kasan.c  | 507 +------------------------------------------
 mm/kasan/kasan.h  |  85 +++++++-
 4 files changed, 633 insertions(+), 507 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 +543 -0

543 lines not on this page · raw message

mm/kasan/kasan.c +2 ~~-505~~

537 lines not on this page · raw message

mm/kasan/kasan.h +84 -1

111 lines not on this page · raw message

Signature · 1 line

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:40 UTC #3 lore raw

PATCH v2 3/16 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              | 76 ++++++++++++++++++++++++++--------
 mm/kasan/Makefile              |  6 ++-
 mm/kasan/khwasan.c             | 75 +++++++++++++++++++++++++++++++++
 mm/slub.c                      |  2 +-
 scripts/Makefile.kasan         | 27 +++++++++++-
 10 files changed, 187 insertions(+), 28 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 +58 ~~-18~~

107 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/khwasan.c new file +75 -0

75 lines not on this page · raw message

mm/slub.c +1 -1

index 46c5b1e481c3..a00503bfc273 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 +25 -2

index 69552a39951d..4893f667a9f0 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

@@ -42,6 +42,29 @@ ifdef CONFIG_KASAN_EXTRA
 CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
 endif
 
-CFLAGS_KASAN_NOSANITIZE := -fno-builtin
+endif
+
+ifdef CONFIG_KASAN_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 := -fsanitize=kernel-hwaddress \
+		-mllvm -hwasan-instrument-stack=0 \
+		$(instrumentation_flags)
+
+ifeq ($(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
+endif
+
+endif
+
+ifdef CONFIG_KASAN
+CFLAGS_KASAN_NOSANITIZE := -fno-builtin
 endif

Signature · 1 line

2.17.0.921.gf22659ad46-goog

Chintan Pandya

2018-06-04 10:28 UTC #4 lore raw

Re: [PATCH v2 03/16] khwasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW

On 5/25/2018 8:10 PM, Andrey Konovalov wrote:
...<snip>

scripts/Makefile.kasan ifdef CONFIG_KASAN_EXTRA · line 59

Quoted 13 lines

scripts/Makefile.kasan +12 -0

+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 := -fsanitize=kernel-hwaddress \
+		-mllvm -hwasan-instrument-stack=0 \
+		$(instrumentation_flags)
+
+ifeq ($(call cc-option, $(CFLAGS_KASAN_MINIMAL) -Werror),)

/s/CFLAGS_KASAN_MINIMAL/CFLAGS_KASAN ??

scripts/Makefile.kasan ifdef CONFIG_KASAN_EXTRA · line 70

Quoted 12 lines

scripts/Makefile.kasan +10 -0

+    ifneq ($(CONFIG_COMPILE_TEST),y)
+        $(warning Cannot use CONFIG_KASAN_HW: \
+            -fsanitize=hwaddress is not supported by compiler)
+    endif
+endif
+
+endif
+
+ifdef CONFIG_KASAN
+CFLAGS_KASAN_NOSANITIZE := -fno-builtin
  endif

Chintan

Signature · 3 lines

Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum, a Linux Foundation
Collaborative Project

Andrey Konovalov

author

2018-06-04 13:58 UTC #5 lore raw

Re: [PATCH v2 03/16] khwasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW

Quoted 5 lines · Chintan Pandya

On 5/25/2018 8:10 PM, Andrey Konovalov wrote:
...<snip>

Quoted 17 lines

scripts/Makefile.kasan ifdef CONFIG_KASAN_EXTRA · line 59

Quoted 13 lines

scripts/Makefile.kasan +11 -1

+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 := -fsanitize=kernel-hwaddress \
+               -mllvm -hwasan-instrument-stack=0 \
+               $(instrumentation_flags)
+
+ifeq ($(call cc-option, $(CFLAGS_KASAN_MINIMAL) -Werror),)

/s/CFLAGS_KASAN_MINIMAL/CFLAGS_KASAN ??

Right, thanks! Will fix in v3.

Andrey Konovalov

author

2018-05-25 14:40 UTC #6 lore raw

PATCH v2 4/16 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 87f7d2f9f17c..99c9649c57b1 100644
@@ -99,7 +99,7 @@ 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:40 UTC #7 lore raw

PATCH v2 5/16 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 12145874c02b..7a31e8ccbad2 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 99a569e18ec7..3d7277cc1f5b 100644
@@ -473,11 +473,12 @@ 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:40 UTC #8 lore raw

PATCH v2 6/16 khwasan, arm64: untag virt address in __kimg_to_phys and _virt_addr_is_linear

In reply to Andrey Konovalov

__kimg_to_phys (which is used by virt_to_phys) and _virt_addr_is_linear (which is used by virt_addr_valid) assume 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 those macros.

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

---
 arch/arm64/include/asm/memory.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

arch/arm64/include/asm/memory.h +18 -0

index 6d084431b7f7..e9e054dfb1fc 100644
@@ -92,6 +92,13 @@
 #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))
+#define KASAN_RESET_TAG(addr)		KASAN_SET_TAG(addr, 0xff)
+#endif
+
 #define MIN_THREAD_SHIFT	(14 + KASAN_THREAD_SHIFT)
 
 /*

@@ -225,7 +232,12 @@ 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_RESET_TAG(addr) - 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);				\

@@ -301,7 +313,13 @@ static inline void *phys_to_virt(phys_addr_t x)
 #endif
 #endif
 
+#ifdef CONFIG_KASAN_HW
+#define _virt_addr_is_linear(kaddr)	(KASAN_RESET_TAG((u64)(kaddr)) >= \
+						PAGE_OFFSET)
+#else
 #define _virt_addr_is_linear(kaddr)	(((u64)(kaddr)) >= PAGE_OFFSET)
+#endif
+
 #define virt_addr_valid(kaddr)		(_virt_addr_is_linear(kaddr) && \
 					 _virt_addr_valid(kaddr))

Signature · 1 line

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:40 UTC #9 lore raw

PATCH v2 7/16 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:40 UTC #10 lore raw

PATCH v2 8/16 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/khwasan.c         | 47 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+)

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

index 7a31e8ccbad2..e7f37c0b7e14 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/khwasan.c +47 -0

53 lines not on this page · raw message

Signature · 1 line

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:41 UTC #11 lore raw

PATCH v2 9/16 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:41 UTC #12 lore raw

PATCH v2 10/16 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:41 UTC #13 lore raw

PATCH v2 11/16 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_report.c   | 158 +++++++++++++++++++++++++
 mm/kasan/khwasan_report.c |  39 +++++++
 mm/kasan/report.c         | 234 +++++++++-----------------------------
 4 files changed, 250 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_report.c new file +158 -0

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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~~

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Signature · 1 line

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:41 UTC #14 lore raw

PATCH v2 12/16 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_report.c   |  7 ++---
 mm/kasan/khwasan_report.c | 21 +++++++++++++++
 mm/kasan/report.c         | 57 +++++++++++++++++++++------------------
 4 files changed, 57 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_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~~

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Signature · 1 line

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:41 UTC #15 lore raw

PATCH v2 13/16 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  | 83 +++++++++++++++++++++++++++++++++++-----------
 mm/kasan/khwasan.c | 40 ++++++++++++++++++++++
 2 files changed, 103 insertions(+), 20 deletions(-)

mm/kasan/common.c +63 ~~-20~~

index 3d7277cc1f5b..8123a61b7e0f 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 +151,20 @@ 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);
+	u8 tag = get_tag(address);
+
+	/* Perform shadow offset calculation based on untagged address */
+	address = reset_tag(address);
+
+	kasan_poison_shadow(address, size, tag);
 
 	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 = tag;
+		else
+			*shadow = size & KASAN_SHADOW_MASK;
 	}
 }

@@ -200,8 +212,9 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark)
 
 void kasan_alloc_pages(struct page *page, unsigned int order)
 {
-	if (likely(!PageHighMem(page)))
-		kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
+	if (unlikely(PageHighMem(page)))
+		return;
+	kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
 }
 
 void kasan_free_pages(struct page *page, unsigned int order)

@@ -235,6 +248,7 @@ 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. */

@@ -242,20 +256,20 @@ 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.

@@ -268,6 +282,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 		return;
 	}
 
+	cache->align = round_up(cache->align, KASAN_SHADOW_SCALE_SIZE);
+
 	*flags |= SLAB_KASAN;
 }

@@ -325,18 +341,41 @@ 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 inline bool shadow_invalid(u8 tag, s8 shadow_byte)
+{
+        if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+                return shadow_byte < 0 ||
+			shadow_byte >= KASAN_SHADOW_SCALE_SIZE;
+        else
+                return tag != (u8)shadow_byte;
 }
 
 static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
 			      unsigned long ip, bool quarantine)
 {
 	s8 shadow_byte;
+	u8 tag;
+	void *tagged_object;
 	unsigned long rounded_up_size;
 
+	tag = get_tag(object);
+	tagged_object = 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(tagged_object, ip);
 		return true;
 	}

@@ -345,20 +384,22 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
 		return false;
 
 	shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
-	if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
-		kasan_report_invalid_free(object, ip);
+	if (shadow_invalid(tag, shadow_byte)) {
+		kasan_report_invalid_free(tagged_object, ip);
 		return true;
 	}
 
 	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)

@@ -371,6 +412,7 @@ 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();

@@ -383,14 +425,15 @@ 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);
 
-	kasan_unpoison_shadow(object, size);
+	tag = random_tag();
+	kasan_unpoison_shadow(set_tag(object, tag), size);
 	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);

@@ -440,7 +483,7 @@ 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;
 		}

@@ -453,7 +496,7 @@ 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/khwasan.c +40 -0

index d34679b8f8c7..fd1725022794 100644
@@ -88,15 +88,52 @@ 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)

@@ -108,15 +145,18 @@ 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:41 UTC #16 lore raw

PATCH v2 14/16 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:41 UTC #17 lore raw

PATCH v2 15/16 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   | 10 ++++++++++
 include/linux/mm.h                | 29 +++++++++++++++++++++++++++++
 include/linux/page-flags-layout.h | 10 ++++++++++
 mm/cma.c                          | 11 +++++++++++
 mm/kasan/common.c                 | 15 +++++++++++++--
 mm/page_alloc.c                   |  1 +
 6 files changed, 74 insertions(+), 2 deletions(-)

arch/arm64/include/asm/memory.h +10 -0

index e9e054dfb1fc..3352a65b8312 100644
@@ -305,7 +305,17 @@ 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);			\
+	__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 c6fa9a255dbf..b79cf6443151 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 +11 -0

index aa40e6c7b042..893f0dff39c0 100644
@@ -468,6 +468,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
 	unsigned long pfn = -1;
 	unsigned long start = 0;
 	unsigned long bitmap_maxno, bitmap_no, bitmap_count;
+	size_t i;
 	struct page *page = NULL;
 	int ret = -ENOMEM;

@@ -527,6 +528,16 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
 
 	trace_cma_alloc(pfn, page, count, align);
 
+	/*
+	 * CMA can allocate multiple page blocks, which results in different
+	 * blocks being marked with different tags. Reset the tags to ignore
+	 * those page blocks.
+	 */
+	if (page) {
+		for (i = 0; i < count; i++)
+			page_kasan_tag_reset(page + i);
+	}
+
 	if (ret && !(gfp_mask & __GFP_NOWARN)) {
 		pr_err("%s: alloc failed, req-size: %zu pages, ret: %d\n",
 			__func__, count, ret);

mm/kasan/common.c +13 -2

index 8123a61b7e0f..041367528470 100644
@@ -212,8 +212,15 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark)
 
 void kasan_alloc_pages(struct page *page, unsigned int order)
 {
+	u8 tag;
+	unsigned long i;
+
 	if (unlikely(PageHighMem(page)))
 		return;
+
+	tag = random_tag();
+	for (i = 0; i < (1 << order); i++)
+		page_kasan_tag_set(page + i, tag);
 	kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
 }

@@ -311,6 +318,10 @@ struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
 
 void kasan_poison_slab(struct page *page)
 {
+	unsigned long i;
+
+	for (i = 0; i < (1 << compound_order(page)); i++)
+		page_kasan_tag_reset(page + i);
 	kasan_poison_shadow(page_address(page),
 			PAGE_SIZE << compound_order(page),
 			KASAN_KMALLOC_REDZONE);

@@ -483,7 +494,7 @@ 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;
 		}

@@ -496,7 +507,7 @@ 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 14:41 UTC #18 lore raw

PATCH v2 16/16 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 | 213 +++++++++++++++++-------------
 1 file changed, 123 insertions(+), 90 deletions(-)

Documentation/dev-tools/kasan.rst +123 ~~-90~~

index f7a18f274357..b77e877353d4 100644
@@ -8,11 +8,19 @@ 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.
+KHWASAN in turns is only supported in clang and requires revision 330044 or
+later.
+
+Currently classic KASAN is supported for the x86_64, arm64 and xtensa
+architectures, and KHWASAN is supported only for arm64.
 
 Usage
 -----

@@ -21,12 +29,14 @@ 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 +53,80 @@ 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 +143,24 @@ 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 +173,34 @@ 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
+of the 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

2.17.0.921.gf22659ad46-goog

Andrey Konovalov

author

2018-05-25 16:35 UTC #19 lore raw

In reply to Andrey Konovalov

Quoted 4 lines · Andrey Konovalov

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.

Nevermind this part about TODOs, forgot to edit that after going from RFC to v1.

Quoted 235 lines

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).
Despite that there's a particular type of bugs that KHWASAN can detect compared to KASAN: use-after-free after the object has been allocated by someone else.
====== Benchmarks
The following numbers were collected on Odroid C2 board. Both KASAN and KHWASAN were used in inline instrumentation mode.
Boot time [1]:
* ~1.7 sec for clean kernel
* ~5.0 sec for KASAN
* ~5.0 sec for KHWASAN
Slab memory usage after boot [2]:
* ~40 kb for clean kernel
* ~105 kb + 1/8th shadow ~= 118 kb for KASAN
* ~47 kb + 1/16th shadow ~= 50 kb for KHWASAN
Network performance [3]:
* 8.33 Gbits/sec for clean kernel
* 3.17 Gbits/sec for KASAN
* 2.85 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 and will be added later.
====== Changes
Changes in v2:
- Changed kmalloc_large_node_hook to return tagged pointer instead of using an output argument.
- Fix checking whether -fsanitize=hwaddress is supported by the compiler.
- Removed duplication of -fno-builtin for KASAN and KHWASAN.
- Removed {} block for one line for_each_possible_cpu loop.
- Made set_track() static inline as it is used only in common.c.
- Moved optimal_redzone() to common.c.
- Fixed using tagged pointer for shadow calculation in kasan_unpoison_shadow().
- Restored setting cache->align in kasan_cache_create(), which was accidentally lost.
- Simplified __kasan_slab_free(), kasan_alloc_pages() and kasan_kmalloc().
- Removed tagging from kasan_kmalloc_large().
- Added page_kasan_tag_reset() to kasan_poison_slab() and removed !PageSlab() check from page_to_virt.
- Reset pointer tag in _virt_addr_is_linear.
- Set page tag for each page when multiple pages are allocated or freed.
- Added a comment as to why we ignore cma allocated pages.
Changes in v1:
- Rebased onto 4.17-rc4.
- Updated benchmarking stats.
- Documented compiler version requirements, memory usage and slowdown.
- Dropped kvm patches, as clang + arm64 + kvm is completely broken [1].
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 [1]).
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.
[1] https://lkml.org/lkml/2018/4/19/775
Andrey Konovalov (16):
khwasan, mm: change kasan hooks signatures
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 and
_virt_addr_is_linear
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      | 213 +++++----
 arch/arm64/Kconfig                     |   1 +
 arch/arm64/Makefile                    |   2 +-
 arch/arm64/include/asm/brk-imm.h       |   2 +
 arch/arm64/include/asm/memory.h        |  41 +-
 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                  |  84 +++-
 include/linux/mm.h                     |  29 ++
 include/linux/page-flags-layout.h      |  10 +
 lib/Kconfig.kasan                      |  76 +++-
 mm/cma.c                               |  11 +
 mm/kasan/Makefile                      |   9 +-
 mm/kasan/common.c                      | 598 +++++++++++++++++++++++++
 mm/kasan/kasan.c                       | 503 +--------------------
 mm/kasan/kasan.h                       |  85 +++-
 mm/kasan/kasan_report.c                | 155 +++++++
 mm/kasan/khwasan.c                     | 162 +++++++
 mm/kasan/khwasan_report.c              |  60 +++
 mm/kasan/report.c                      | 271 +++--------
 mm/page_alloc.c                        |   1 +
 mm/slab.c                              |  12 +-
 mm/slab.h                              |   2 +-
 mm/slab_common.c                       |   6 +-
 mm/slub.c                              |  17 +-
 scripts/Makefile.kasan                 |  27 +-
 32 files changed, 1630 insertions(+), 858 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
--
2.17.0.921.gf22659ad46-goog