Make red zone size more flexible for stack variables (PR sanitizer/81715).

2018-11-30  Martin Liska  <mliska@suse.cz>

	PR sanitizer/81715
	* asan.c (asan_shadow_cst): Remove, partially transform
	into flush_redzone_payload.
	(RZ_BUFFER_SIZE): New.
	(struct asan_redzone_buffer): New.
	(asan_redzone_buffer::emit_redzone_byte): Likewise.
	(asan_redzone_buffer::flush_redzone_payload): Likewise.
	(asan_redzone_buffer::flush_if_full): Likewise.
	(asan_emit_stack_protection): Use asan_redzone_buffer class
	that is responsible for proper aligned stores and flushing
	of shadow memory payload.
	* asan.h (ASAN_MIN_RED_ZONE_SIZE): New.
	(asan_var_and_redzone_size): Likewise.
	* cfgexpand.c (expand_stack_vars): Use smaller alignment
	(ASAN_MIN_RED_ZONE_SIZE) in order to make shadow memory
	for automatic variables more compact.
2018-11-30  Martin Liska  <mliska@suse.cz>

	PR sanitizer/81715
	* c-c++-common/asan/asan-stack-small.c: New test.

From-SVN: r266664

1 files changed, 25 insertions, 0 deletions

diff --git a/gcc/asan.h b/gcc/asan.h
index 2f431b4..e1b9b49 100644
--- a/gcc/asan.h
+++ b/gcc/asan.h
@@ -53,6 +53,11 @@ extern hash_set <tree> *asan_used_labels;
    up to 2 * ASAN_RED_ZONE_SIZE - 1 bytes.  */
 #define ASAN_RED_ZONE_SIZE	32
 
+/* Stack variable use more compact red zones.  The size includes also
+   size of variable itself.  */
+
+#define ASAN_MIN_RED_ZONE_SIZE	16
+
 /* Shadow memory values for stack protection.  Left is below protected vars,
    the first pointer in stack corresponding to that offset contains
    ASAN_STACK_FRAME_MAGIC word, the second pointer to a string describing
@@ -102,6 +107,26 @@ asan_red_zone_size (unsigned int size)
   return c ? 2 * ASAN_RED_ZONE_SIZE - c : ASAN_RED_ZONE_SIZE;
 }
 
+/* Return how much a stack variable occupis on a stack
+   including a space for red zone.  */
+
+static inline unsigned HOST_WIDE_INT
+asan_var_and_redzone_size (unsigned HOST_WIDE_INT size)
+{
+  if (size <= 4)
+    return 16;
+  else if (size <= 16)
+    return 32;
+  else if (size <= 128)
+    return size + 32;
+  else if (size <= 512)
+    return size + 64;
+  else if (size <= 4096)
+    return size + 128;
+  else
+    return size + 256;
+}
+
 extern bool set_asan_shadow_offset (const char *);
 
 extern void set_sanitized_sections (const char *);