[PATCH v4 0/5] kasan: support alloca, LLVM

[PATCH v4 0/5] kasan: support alloca, LLVM

[Paul Lawrence]

[PATCH v3 1/5] kasan: add compiler support for clang
  No change

[PATCH v3 2/5] kasan/Makefile: Support LLVM style asan parameters.
  Correctly attributed
  Changed to use strip to work in all environments

[PATCH v3 3/5] kasan: support alloca() poisoning
  No change

[PATCH v3 4/5] kasan: Add tests for alloca poisoning
  No change

[PATCH v3 5/5] kasan: added functions for unpoisoning stack variables
  No change
 

Paul Lawrence (5):
  kasan: add compiler support for clang
  kasan/Makefile: Support LLVM style asan parameters.
  kasan: support alloca() poisoning
  kasan: Add tests for alloca poisonong
  kasan: added functions for unpoisoning stack variables

 include/linux/compiler-clang.h |  8 +++++++
 lib/test_kasan.c               | 22 +++++++++++++++++++
 mm/kasan/kasan.c               | 49 ++++++++++++++++++++++++++++++++++++++++++
 mm/kasan/kasan.h               |  8 +++++++
 mm/kasan/report.c              |  4 ++++
 scripts/Makefile.kasan         | 30 ++++++++++++++++----------
 6 files changed, 110 insertions(+), 11 deletions(-)

-- 
2.15.0.531.g2ccb3012c9-goog

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[PATCH v4 1/5] kasan: add compiler support for clang

[Paul Lawrence]

For now we can hard-code ASAN ABI level 5, since historical clang builds
can't build the kernel anyway.  We also need to emulate gcc's
__SANITIZE_ADDRESS__ flag, or memset() calls won't be instrumented.

Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 include/linux/compiler-clang.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 3b609edffa8f..d02a4df3f473 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -19,3 +19,11 @@
 
 #define randomized_struct_fields_start	struct {
 #define randomized_struct_fields_end	};
+
+/* all clang versions usable with the kernel support KASAN ABI version 5 */
+#define KASAN_ABI_VERSION 5
+
+/* emulate gcc's __SANITIZE_ADDRESS__ flag */
+#if __has_feature(address_sanitizer)
+#define __SANITIZE_ADDRESS__
+#endif
-- 
2.15.0.531.g2ccb3012c9-goog

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Re: [PATCH v4 1/5] kasan: add compiler support for clang

[Andrey Ryabinin]

On 12/04/2017 10:17 PM, Paul Lawrence wrote:
> For now we can hard-code ASAN ABI level 5, since historical clang builds
> can't build the kernel anyway.  We also need to emulate gcc's
> __SANITIZE_ADDRESS__ flag, or memset() calls won't be instrumented.
> 
> Signed-off-by: Greg Hackmann <ghackmann@google.com>
> Signed-off-by: Paul Lawrence <paullawrence@google.com>
> ---

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

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[PATCH v4 2/5] kasan/Makefile: Support LLVM style asan parameters.

[Paul Lawrence]

From: Andrey Ryabinin <aryabinin@virtuozzo.com>

LLVM doesn't understand GCC-style paramters ("--param asan-foo=bar"),
thus we currently we don't use inline/globals/stack instrumentation
when building the kernel with clang.

Add support for LLVM-style parameters ("-mllvm -asan-foo=bar") to
enable all KASAN features.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 scripts/Makefile.kasan | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 1ce7115aa499..d5a1a4b6d079 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -10,10 +10,7 @@ KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)
 
 CFLAGS_KASAN_MINIMAL := -fsanitize=kernel-address
 
-CFLAGS_KASAN := $(call cc-option, -fsanitize=kernel-address \
-		-fasan-shadow-offset=$(KASAN_SHADOW_OFFSET) \
-		--param asan-stack=1 --param asan-globals=1 \
-		--param asan-instrumentation-with-call-threshold=$(call_threshold))
+cc-param = $(call cc-option, -mllvm -$(1), $(call cc-option, --param $(1)))
 
 ifeq ($(call cc-option, $(CFLAGS_KASAN_MINIMAL) -Werror),)
    ifneq ($(CONFIG_COMPILE_TEST),y)
@@ -21,13 +18,23 @@ ifeq ($(call cc-option, $(CFLAGS_KASAN_MINIMAL) -Werror),)
             -fsanitize=kernel-address is not supported by compiler)
    endif
 else
-    ifeq ($(CFLAGS_KASAN),)
-        ifneq ($(CONFIG_COMPILE_TEST),y)
-            $(warning CONFIG_KASAN: compiler does not support all options.\
-                Trying minimal configuration)
-        endif
-        CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL)
-    endif
+   # -fasan-shadow-offset fails without -fsanitize
+   CFLAGS_KASAN_SHADOW := $(call cc-option, -fsanitize=kernel-address \
+			-fasan-shadow-offset=$(KASAN_SHADOW_OFFSET), \
+			$(call cc-option, -fsanitize=kernel-address \
+			-mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))
+
+   ifeq ($(strip $(CFLAGS_KASAN_SHADOW)),)
+      CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL)
+   else
+      # Now add all the compiler specific options that are valid standalone
+      CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \
+	$(call cc-param,asan-globals=1) \
+	$(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
+	$(call cc-param,asan-stack=1) \
+	$(call cc-param,asan-use-after-scope=1)
+   endif
+
 endif
 
 CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
-- 
2.15.0.531.g2ccb3012c9-goog

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Re: [PATCH v4 2/5] kasan/Makefile: Support LLVM style asan parameters.

[Alexander Potapenko]

On Mon, Dec 4, 2017 at 8:17 PM, Paul Lawrence <paullawrence@google.com> wrote:
> From: Andrey Ryabinin <aryabinin@virtuozzo.com>
>
> LLVM doesn't understand GCC-style paramters ("--param asan-foo=bar"),
> thus we currently we don't use inline/globals/stack instrumentation
> when building the kernel with clang.
>
> Add support for LLVM-style parameters ("-mllvm -asan-foo=bar") to
> enable all KASAN features.
>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Signed-off-by: Paul Lawrence <paullawrence@google.com>
> ---
>  scripts/Makefile.kasan | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index 1ce7115aa499..d5a1a4b6d079 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -10,10 +10,7 @@ KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)
>
>  CFLAGS_KASAN_MINIMAL := -fsanitize=kernel-address
>
> -CFLAGS_KASAN := $(call cc-option, -fsanitize=kernel-address \
> -               -fasan-shadow-offset=$(KASAN_SHADOW_OFFSET) \
> -               --param asan-stack=1 --param asan-globals=1 \
> -               --param asan-instrumentation-with-call-threshold=$(call_threshold))
> +cc-param = $(call cc-option, -mllvm -$(1), $(call cc-option, --param $(1)))
>
>  ifeq ($(call cc-option, $(CFLAGS_KASAN_MINIMAL) -Werror),)
>     ifneq ($(CONFIG_COMPILE_TEST),y)
> @@ -21,13 +18,23 @@ ifeq ($(call cc-option, $(CFLAGS_KASAN_MINIMAL) -Werror),)
>              -fsanitize=kernel-address is not supported by compiler)
>     endif
>  else
> -    ifeq ($(CFLAGS_KASAN),)
> -        ifneq ($(CONFIG_COMPILE_TEST),y)
> -            $(warning CONFIG_KASAN: compiler does not support all options.\
> -                Trying minimal configuration)
> -        endif
> -        CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL)
> -    endif
> +   # -fasan-shadow-offset fails without -fsanitize
Would be nice to have a comment here explaining that
-fasan-shadow-offset is a GCC flag whereas -asan-mapping-offset is an
LLVM one.
> +   CFLAGS_KASAN_SHADOW := $(call cc-option, -fsanitize=kernel-address \
> +                       -fasan-shadow-offset=$(KASAN_SHADOW_OFFSET), \
> +                       $(call cc-option, -fsanitize=kernel-address \
> +                       -mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))
> +
> +   ifeq ($(strip $(CFLAGS_KASAN_SHADOW)),)
> +      CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL)
> +   else
> +      # Now add all the compiler specific options that are valid standalone
> +      CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \
> +       $(call cc-param,asan-globals=1) \
> +       $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
> +       $(call cc-param,asan-stack=1) \
> +       $(call cc-param,asan-use-after-scope=1)
> +   endif
> +
>  endif
>
>  CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
> --
> 2.15.0.531.g2ccb3012c9-goog
>
Reviewed-by: Alexander Potapenko <glider@google.com>


-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

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[PATCH v4 3/5] kasan: support alloca() poisoning

[Paul Lawrence]

clang's AddressSanitizer implementation adds redzones on either side of
alloca()ed buffers.  These redzones are 32-byte aligned and at least 32
bytes long.

__asan_alloca_poison() is passed the size and address of the allocated
buffer, *excluding* the redzones on either side.  The left redzone will
always be to the immediate left of this buffer; but AddressSanitizer may
need to add padding between the end of the buffer and the right redzone.
If there are any 8-byte chunks inside this padding, we should poison
those too.

__asan_allocas_unpoison() is just passed the top and bottom of the
dynamic stack area, so unpoisoning is simpler.

Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 mm/kasan/kasan.c       | 34 ++++++++++++++++++++++++++++++++++
 mm/kasan/kasan.h       |  8 ++++++++
 mm/kasan/report.c      |  4 ++++
 scripts/Makefile.kasan |  3 ++-
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 405bba487df5..d96b36088b2f 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -736,6 +736,40 @@ void __asan_unpoison_stack_memory(const void *addr, size_t size)
 }
 EXPORT_SYMBOL(__asan_unpoison_stack_memory);
 
+/* Emitted by compiler to poison alloca()ed objects. */
+void __asan_alloca_poison(unsigned long addr, size_t size)
+{
+	size_t rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
+	size_t padding_size = round_up(size, KASAN_ALLOCA_REDZONE_SIZE) -
+			rounded_up_size;
+	size_t rounded_down_size = round_down(size, KASAN_SHADOW_SCALE_SIZE);
+
+	const void *left_redzone = (const void *)(addr -
+			KASAN_ALLOCA_REDZONE_SIZE);
+	const void *right_redzone = (const void *)(addr + rounded_up_size);
+
+	WARN_ON(!IS_ALIGNED(addr, KASAN_ALLOCA_REDZONE_SIZE));
+
+	kasan_unpoison_shadow((const void *)(addr + rounded_down_size),
+			      size - rounded_down_size);
+	kasan_poison_shadow(left_redzone, KASAN_ALLOCA_REDZONE_SIZE,
+			KASAN_ALLOCA_LEFT);
+	kasan_poison_shadow(right_redzone,
+			padding_size + KASAN_ALLOCA_REDZONE_SIZE,
+			KASAN_ALLOCA_RIGHT);
+}
+EXPORT_SYMBOL(__asan_alloca_poison);
+
+/* Emitted by compiler to unpoison alloca()ed areas when the stack unwinds. */
+void __asan_allocas_unpoison(const void *stack_top, const void *stack_bottom)
+{
+	if (unlikely(!stack_top || stack_top > stack_bottom))
+		return;
+
+	kasan_unpoison_shadow(stack_top, stack_bottom - stack_top);
+}
+EXPORT_SYMBOL(__asan_allocas_unpoison);
+
 #ifdef CONFIG_MEMORY_HOTPLUG
 static int __meminit kasan_mem_notifier(struct notifier_block *nb,
 			unsigned long action, void *data)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index c70851a9a6a4..7c0bcd1f4c0d 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -24,6 +24,14 @@
 #define KASAN_STACK_PARTIAL     0xF4
 #define KASAN_USE_AFTER_SCOPE   0xF8
 
+/*
+ * alloca redzone shadow values
+ */
+#define KASAN_ALLOCA_LEFT	0xCA
+#define KASAN_ALLOCA_RIGHT	0xCB
+
+#define KASAN_ALLOCA_REDZONE_SIZE	32
+
 /* Don't break randconfig/all*config builds */
 #ifndef KASAN_ABI_VERSION
 #define KASAN_ABI_VERSION 1
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 410c8235e671..eff12e040498 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -102,6 +102,10 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info)
 	case KASAN_USE_AFTER_SCOPE:
 		bug_type = "use-after-scope";
 		break;
+	case KASAN_ALLOCA_LEFT:
+	case KASAN_ALLOCA_RIGHT:
+		bug_type = "alloca-out-of-bounds";
+		break;
 	}
 
 	return bug_type;
diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index d5a1a4b6d079..dbbd4382f15a 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -32,7 +32,8 @@ else
 	$(call cc-param,asan-globals=1) \
 	$(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
 	$(call cc-param,asan-stack=1) \
-	$(call cc-param,asan-use-after-scope=1)
+	$(call cc-param,asan-use-after-scope=1) \
+	$(call cc-param,asan-instrument-allocas=1)
    endif
 
 endif
-- 
2.15.0.531.g2ccb3012c9-goog

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Re: [PATCH v4 3/5] kasan: support alloca() poisoning

[Andrey Ryabinin]

On 12/04/2017 10:17 PM, Paul Lawrence wrote:
> clang's AddressSanitizer implementation adds redzones on either side of
> alloca()ed buffers.  These redzones are 32-byte aligned and at least 32
> bytes long.
> 
> __asan_alloca_poison() is passed the size and address of the allocated
> buffer, *excluding* the redzones on either side.  The left redzone will
> always be to the immediate left of this buffer; but AddressSanitizer may
> need to add padding between the end of the buffer and the right redzone.
> If there are any 8-byte chunks inside this padding, we should poison
> those too.
> 
> __asan_allocas_unpoison() is just passed the top and bottom of the
> dynamic stack area, so unpoisoning is simpler.
> 
> Signed-off-by: Greg Hackmann <ghackmann@google.com>
> Signed-off-by: Paul Lawrence <paullawrence@google.com>
> ---

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

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[PATCH v4 4/5] kasan: Add tests for alloca poisoning

[Paul Lawrence]

Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 lib/test_kasan.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index ef1a3ac1397e..2724f86c4cef 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -472,6 +472,26 @@ static noinline void __init use_after_scope_test(void)
 	p[1023] = 1;
 }
 
+static noinline void __init kasan_alloca_oob_left(void)
+{
+	volatile int i = 10;
+	char alloca_array[i];
+	char *p = alloca_array - 1;
+
+	pr_info("out-of-bounds to left on alloca\n");
+	*(volatile char *)p;
+}
+
+static noinline void __init kasan_alloca_oob_right(void)
+{
+	volatile int i = 10;
+	char alloca_array[i];
+	char *p = alloca_array + i;
+
+	pr_info("out-of-bounds to right on alloca\n");
+	*(volatile char *)p;
+}
+
 static int __init kmalloc_tests_init(void)
 {
 	/*
@@ -502,6 +522,8 @@ static int __init kmalloc_tests_init(void)
 	memcg_accounted_kmem_cache();
 	kasan_stack_oob();
 	kasan_global_oob();
+	kasan_alloca_oob_left();
+	kasan_alloca_oob_right();
 	ksize_unpoisons_memory();
 	copy_user_test();
 	use_after_scope_test();
-- 
2.15.0.531.g2ccb3012c9-goog

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Re: [PATCH v4 4/5] kasan: Add tests for alloca poisoning

[Andrey Ryabinin]

On 12/04/2017 10:17 PM, Paul Lawrence wrote:
> Signed-off-by: Greg Hackmann <ghackmann@google.com>
> Signed-off-by: Paul Lawrence <paullawrence@google.com>
> ---
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

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[PATCH v4 5/5] kasan: added functions for unpoisoning stack variables

[Paul Lawrence]

From: Alexander Potapenko <glider@google.com>

As a code-size optimization, LLVM builds since r279383 may
bulk-manipulate the shadow region when (un)poisoning large memory
blocks.  This requires new callbacks that simply do an uninstrumented
memset().

This fixes linking the Clang-built kernel when using KASAN.

Signed-off-by: Alexander Potapenko <glider@google.com>
[ghackmann@google.com: fix memset() parameters, and tweak
 commit message to describe new callbacks]
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 mm/kasan/kasan.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index d96b36088b2f..8aaee42fcfab 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -770,6 +770,21 @@ void __asan_allocas_unpoison(const void *stack_top, const void *stack_bottom)
 }
 EXPORT_SYMBOL(__asan_allocas_unpoison);
 
+/* Emitted by the compiler to [un]poison local variables. */
+#define DEFINE_ASAN_SET_SHADOW(byte) \
+	void __asan_set_shadow_##byte(const void *addr, size_t size)	\
+	{								\
+		__memset((void *)addr, 0x##byte, size);			\
+	}								\
+	EXPORT_SYMBOL(__asan_set_shadow_##byte)
+
+DEFINE_ASAN_SET_SHADOW(00);
+DEFINE_ASAN_SET_SHADOW(f1);
+DEFINE_ASAN_SET_SHADOW(f2);
+DEFINE_ASAN_SET_SHADOW(f3);
+DEFINE_ASAN_SET_SHADOW(f5);
+DEFINE_ASAN_SET_SHADOW(f8);
+
 #ifdef CONFIG_MEMORY_HOTPLUG
 static int __meminit kasan_mem_notifier(struct notifier_block *nb,
 			unsigned long action, void *data)
-- 
2.15.0.531.g2ccb3012c9-goog

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Re: [PATCH v4 5/5] kasan: added functions for unpoisoning stack variables

[Andrey Ryabinin]

On 12/04/2017 10:17 PM, Paul Lawrence wrote:
> From: Alexander Potapenko <glider@google.com>
> 
> As a code-size optimization, LLVM builds since r279383 may
> bulk-manipulate the shadow region when (un)poisoning large memory
> blocks.  This requires new callbacks that simply do an uninstrumented
> memset().
> 
> This fixes linking the Clang-built kernel when using KASAN.
> 
> Signed-off-by: Alexander Potapenko <glider@google.com>
> [ghackmann@google.com: fix memset() parameters, and tweak
>  commit message to describe new callbacks]
> Signed-off-by: Greg Hackmann <ghackmann@google.com>
> Signed-off-by: Paul Lawrence <paullawrence@google.com>
> ---

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

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