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