core: asan: provide asan_memset_unchecked()

Provides asan_memset_unchecked() which does a memset that isn't checked
against the tagging in the ASAN shadow area. If ASAN isn't enabled it's
replaced by a direct call to memset().

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

core/include/kernel/asan.h

@@ -45,6 +45,7 @@ void asan_start(void);
 void asan_tag_no_access(const void *begin, const void *end);
 void asan_tag_access(const void *begin, const void *end);
 void asan_tag_heap_free(const void *begin, const void *end);
+void *asan_memset_unchecked(void *s, int c, size_t n);
 #else
 static inline void asan_tag_no_access(const void *begin __unused,
 				      const void *end __unused)
@@ -58,6 +59,12 @@ static inline void asan_tag_heap_free(const void *begin __unused,
 				      const void *end __unused)
 {
 }
+
+static inline void *asan_memset_unchecked(void *s, int c, size_t n)
+{
+	return memset(s, c, n);
+}
+
 #endif
 
 #endif /*ASM*/

core/kernel/asan.c

@@ -116,8 +116,8 @@ void asan_tag_no_access(const void *begin, const void *end)
 	assert(va_is_well_aligned(end));
 	assert(va_range_inside_shadow(begin, end));
 
-	memset(va_to_shadow(begin), ASAN_DATA_RED_ZONE,
-	       va_range_to_shadow_size(begin, end));
+	asan_memset_unchecked(va_to_shadow(begin), ASAN_DATA_RED_ZONE,
+			      va_range_to_shadow_size(begin, end));
 }
 
 void asan_tag_access(const void *begin, const void *end)
@@ -128,7 +128,8 @@ void asan_tag_access(const void *begin, const void *end)
 	assert(va_range_inside_shadow(begin, end));
 	assert(va_is_well_aligned(begin));
 
-	memset(va_to_shadow(begin), 0, va_range_to_shadow_size(begin, end));
+	asan_memset_unchecked(va_to_shadow(begin), 0,
+			      va_range_to_shadow_size(begin, end));
 	if (!va_is_well_aligned(end))
 		*va_to_shadow(end) = ASAN_BLOCK_SIZE - va_misalignment(end);
 }
@@ -142,8 +143,19 @@ void asan_tag_heap_free(const void *begin, const void *end)
 	assert(va_is_well_aligned(begin));
 	assert(va_is_well_aligned(end));
 
-	memset(va_to_shadow(begin), ASAN_HEAP_RED_ZONE,
-	       va_range_to_shadow_size(begin, end));
+	asan_memset_unchecked(va_to_shadow(begin), ASAN_HEAP_RED_ZONE,
+			      va_range_to_shadow_size(begin, end));
+}
+
+void *asan_memset_unchecked(void *s, int c, size_t n)
+{
+	uint8_t *b = s;
+	size_t m;
+
+	for (m = 0; m < n; m++)
+		b[m] = c;
+
+	return s;
 }
 
 void asan_start(void)