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Re: libsanitizer merge from upstream r191666


On Tue, Oct 29, 2013 at 07:05:49AM -0700, Konstantin Serebryany wrote:
> The calls are emitted by default, but the __asan_stack_malloc call is
> done under a run-time flag
> __asan_option_detect_stack_use_after_return.
> So, to use the stack-use-after-return feature you should simply
> compile with -fsanitize=address and then at run-time
> pass ASAN_OPTIONS=detect_stack_use_after_return=1
> For small stack frame sizes the call to __asan_stack_free is inlined
> (as a performance optimization, not mandatory).

Ok, here is heavily untested implementation of the use after return
sanitization.  Tested just by eyeballing assembly generated for some
testcases and on stack-use-after-return.cc and testing asan.exp (but that
has no use-after-return tests, right?).

What I'm not very happy about is that __asan_stack_malloc_N doesn't have
align argument, is there at least some guaranteed alignment on what it
returns that gcc can hardcode (and if the required alignment is bigger, just
don't call __asan_stack_malloc_N)?  I mean, e.g. on x86_64/i686, right now
say for -mavx code quite often 256-bit alignment is needed, with -mavx512f
512-bit alignment will be needed from time to time.  So if for now
libasan could guarantee 64-byte alignment of the stack chunks or at least
32-byte alignment, I could pass the required alignment to
asan_emit_stack_protection and force no __asan_stack_malloc_N use if
the required alignment is smaller than the one guaranteed by libasan.

2013-11-14  Jakub Jelinek  <jakub@redhat.com>

	* cfgexpand.c (struct stack_vars_data): Add asan_base field.
	(expand_stack_vars): For -fsanitize=address, use (and set initially)
	data->asan_base as base for vars.
	(expand_used_vars): Initialize data.asan_base.  Pass it to
	asan_emit_stack_protection.
	* asan.c (asan_detect_stack_use_after_return): New variable.
	(asan_emit_stack_protection): Add pbase argument.  Implement use
	after return sanitization.
	* asan.h (asan_emit_stack_protection): Adjust prototype.
	(ASAN_STACK_MAGIC_USE_AFTER_RET, ASAN_STACK_RETIRED_MAGIC): Define.

--- gcc/cfgexpand.c.jj	2013-11-14 09:10:08.000000000 +0100
+++ gcc/cfgexpand.c	2013-11-14 12:42:25.194538823 +0100
@@ -879,6 +879,9 @@ struct stack_vars_data
 
   /* Vector of partition representative decls in between the paddings.  */
   vec<tree> asan_decl_vec;
+
+  /* Base pseudo register for Address Sanitizer protected automatic vars.  */
+  rtx asan_base;
 };
 
 /* A subroutine of expand_used_vars.  Give each partition representative
@@ -963,6 +966,7 @@ expand_stack_vars (bool (*pred) (size_t)
       alignb = stack_vars[i].alignb;
       if (alignb * BITS_PER_UNIT <= MAX_SUPPORTED_STACK_ALIGNMENT)
 	{
+	  base = virtual_stack_vars_rtx;
 	  if ((flag_sanitize & SANITIZE_ADDRESS) && pred)
 	    {
 	      HOST_WIDE_INT prev_offset = frame_offset;
@@ -991,10 +995,12 @@ expand_stack_vars (bool (*pred) (size_t)
 	      if (repr_decl == NULL_TREE)
 		repr_decl = stack_vars[i].decl;
 	      data->asan_decl_vec.safe_push (repr_decl);
+	      if (data->asan_base == NULL)
+		data->asan_base = gen_reg_rtx (Pmode);
+	      base = data->asan_base;
 	    }
 	  else
 	    offset = alloc_stack_frame_space (stack_vars[i].size, alignb);
-	  base = virtual_stack_vars_rtx;
 	  base_align = crtl->max_used_stack_slot_alignment;
 	}
       else
@@ -1768,6 +1774,7 @@ expand_used_vars (void)
 
       data.asan_vec = vNULL;
       data.asan_decl_vec = vNULL;
+      data.asan_base = NULL_RTX;
 
       /* Reorder decls to be protected by iterating over the variables
 	 array multiple times, and allocating out of each phase in turn.  */
@@ -1800,8 +1807,9 @@ expand_used_vars (void)
 
 	  var_end_seq
 	    = asan_emit_stack_protection (virtual_stack_vars_rtx,
+					  data.asan_base,
 					  data.asan_vec.address (),
-					  data.asan_decl_vec. address (),
+					  data.asan_decl_vec.address (),
 					  data.asan_vec.length ());
 	}
 
--- gcc/asan.c.jj	2013-11-14 09:10:08.000000000 +0100
+++ gcc/asan.c	2013-11-14 16:06:42.203713457 +0100
@@ -226,6 +226,9 @@ alias_set_type asan_shadow_set = -1;
    alias set is used for all shadow memory accesses.  */
 static GTY(()) tree shadow_ptr_types[2];
 
+/* Decl for __asan_option_detect_stack_use_after_return.  */
+static GTY(()) tree asan_detect_stack_use_after_return;
+
 /* Hashtable support for memory references used by gimple
    statements.  */
 
@@ -939,20 +942,25 @@ asan_function_start (void)
    and DECLS is an array of representative decls for each var partition.
    LENGTH is the length of the OFFSETS array, DECLS array is LENGTH / 2 - 1
    elements long (OFFSETS include gap before the first variable as well
-   as gaps after each stack variable).  */
+   as gaps after each stack variable).  PBASE is, if non-NULL, some pseudo
+   register which stack vars DECL_RTLs are based on.  Either BASE should be
+   assigned to PBASE, when not doing use after return protection, or
+   corresponding address based on __asan_stack_malloc* return value.  */
 
 rtx
-asan_emit_stack_protection (rtx base, HOST_WIDE_INT *offsets, tree *decls,
-			    int length)
+asan_emit_stack_protection (rtx base, rtx pbase, HOST_WIDE_INT *offsets,
+			    tree *decls, int length)
 {
-  rtx shadow_base, shadow_mem, ret, mem;
+  rtx shadow_base, shadow_mem, ret, mem, orig_base, lab;
   char buf[30];
   unsigned char shadow_bytes[4];
   HOST_WIDE_INT base_offset = offsets[length - 1], offset, prev_offset;
+  HOST_WIDE_INT asan_frame_size = offsets[0] - base_offset;
   HOST_WIDE_INT last_offset, last_size;
   int l;
   unsigned char cur_shadow_byte = ASAN_STACK_MAGIC_LEFT;
   tree str_cst, decl, id;
+  int use_after_return_class = -1;
 
   if (shadow_ptr_types[0] == NULL_TREE)
     asan_init_shadow_ptr_types ();
@@ -982,9 +990,53 @@ asan_emit_stack_protection (rtx base, HO
   str_cst = asan_pp_string (&asan_pp);
 
   /* Emit the prologue sequence.  */
+  if (asan_frame_size > 32 && asan_frame_size <= 65536 && pbase)
+    use_after_return_class = floor_log2 (asan_frame_size - 1) - 5;
+  if (use_after_return_class == -1 && pbase)
+    emit_move_insn (pbase, base);
   base = expand_binop (Pmode, add_optab, base,
 		       gen_int_mode (base_offset, Pmode),
 		       NULL_RTX, 1, OPTAB_DIRECT);
+  orig_base = NULL_RTX;
+  if (use_after_return_class != -1)
+    {
+      if (asan_detect_stack_use_after_return == NULL_TREE)
+	{
+	  id = get_identifier ("__asan_option_detect_stack_use_after_return");
+	  decl = build_decl (BUILTINS_LOCATION, VAR_DECL, id,
+			     integer_type_node);
+	  SET_DECL_ASSEMBLER_NAME (decl, id);
+	  TREE_ADDRESSABLE (decl) = 1;
+	  DECL_ARTIFICIAL (decl) = 1;
+	  DECL_IGNORED_P (decl) = 1;
+	  DECL_EXTERNAL (decl) = 1;
+	  TREE_STATIC (decl) = 1;
+	  TREE_PUBLIC (decl) = 1;
+	  TREE_USED (decl) = 1;
+	  asan_detect_stack_use_after_return = decl;
+	}
+      orig_base = gen_reg_rtx (Pmode);
+      emit_move_insn (orig_base, base);
+      ret = expand_normal (asan_detect_stack_use_after_return);
+      lab = gen_label_rtx ();
+      int very_likely = REG_BR_PROB_BASE - (REG_BR_PROB_BASE / 2000 - 1);
+      emit_cmp_and_jump_insns (ret, const0_rtx, EQ, NULL_RTX,
+			       VOIDmode, 0, lab, very_likely);
+      snprintf (buf, sizeof buf, "__asan_stack_malloc_%d",
+		use_after_return_class);
+      ret = init_one_libfunc (buf);
+      rtx addr = convert_memory_address (ptr_mode, base);
+      ret = emit_library_call_value (ret, NULL_RTX, LCT_NORMAL, ptr_mode, 2,
+				     GEN_INT (asan_frame_size),
+				     TYPE_MODE (pointer_sized_int_node),
+				     addr, ptr_mode);
+      ret = convert_memory_address (Pmode, ret);
+      emit_move_insn (base, ret);
+      emit_label (lab);
+      emit_move_insn (pbase, expand_binop (Pmode, add_optab, base,
+					   gen_int_mode (-base_offset, Pmode),
+					   NULL_RTX, 1, OPTAB_DIRECT));
+    }
   mem = gen_rtx_MEM (ptr_mode, base);
   emit_move_insn (mem, gen_int_mode (ASAN_STACK_FRAME_MAGIC, ptr_mode));
   mem = adjust_address (mem, VOIDmode, GET_MODE_SIZE (ptr_mode));
@@ -1006,10 +1058,8 @@ asan_emit_stack_protection (rtx base, HO
   shadow_base = expand_binop (Pmode, lshr_optab, base,
 			      GEN_INT (ASAN_SHADOW_SHIFT),
 			      NULL_RTX, 1, OPTAB_DIRECT);
-  shadow_base = expand_binop (Pmode, add_optab, shadow_base,
-			      gen_int_mode (targetm.asan_shadow_offset (),
-					    Pmode),
-			      NULL_RTX, 1, OPTAB_DIRECT);
+  shadow_base
+    = plus_constant (Pmode, shadow_base, targetm.asan_shadow_offset ());
   gcc_assert (asan_shadow_set != -1
 	      && (ASAN_RED_ZONE_SIZE >> ASAN_SHADOW_SHIFT) == 4);
   shadow_mem = gen_rtx_MEM (SImode, shadow_base);
@@ -1060,6 +1110,47 @@ asan_emit_stack_protection (rtx base, HO
   /* Construct epilogue sequence.  */
   start_sequence ();
 
+  lab = NULL_RTX;  
+  if (use_after_return_class != -1)
+    {
+      rtx lab2 = gen_label_rtx ();
+      char c = (char) ASAN_STACK_MAGIC_USE_AFTER_RET;
+      int very_likely = REG_BR_PROB_BASE - (REG_BR_PROB_BASE / 2000 - 1);
+      emit_cmp_and_jump_insns (orig_base, base, EQ, NULL_RTX,
+			       VOIDmode, 0, lab2, very_likely);
+      shadow_mem = gen_rtx_MEM (BLKmode, shadow_base);
+      set_mem_alias_set (shadow_mem, asan_shadow_set);
+      mem = gen_rtx_MEM (ptr_mode, base);
+      emit_move_insn (mem, gen_int_mode (ASAN_STACK_RETIRED_MAGIC, ptr_mode));
+      if (use_after_return_class < 5
+	  && can_store_by_pieces (asan_frame_size >> ASAN_SHADOW_SHIFT,
+				  builtin_memset_read_str, &c, BITS_PER_UNIT,
+				  true))
+	store_by_pieces (shadow_mem, asan_frame_size >> ASAN_SHADOW_SHIFT,
+			 builtin_memset_read_str, &c, BITS_PER_UNIT, true, 0);
+      else if (use_after_return_class >= 5
+	       || !set_storage_via_setmem (shadow_mem,
+					   GEN_INT (asan_frame_size
+						    >> ASAN_SHADOW_SHIFT),
+					   gen_int_mode (c, QImode),
+					   BITS_PER_UNIT, BITS_PER_UNIT,
+					   -1))
+	{
+	  snprintf (buf, sizeof buf, "__asan_stack_free_%d",
+		    use_after_return_class);
+	  ret = init_one_libfunc (buf);
+	  rtx addr = convert_memory_address (ptr_mode, base);
+	  rtx orig_addr = convert_memory_address (ptr_mode, orig_base);
+	  emit_library_call (ret, LCT_NORMAL, ptr_mode, 3, addr, ptr_mode,
+			     GEN_INT (asan_frame_size),
+			     TYPE_MODE (pointer_sized_int_node),
+			     orig_addr, ptr_mode);
+	}
+      lab = gen_label_rtx ();
+      emit_jump (lab);
+      emit_label (lab2);
+    }
+
   shadow_mem = gen_rtx_MEM (BLKmode, shadow_base);
   set_mem_alias_set (shadow_mem, asan_shadow_set);
   prev_offset = base_offset;
@@ -1092,6 +1183,8 @@ asan_emit_stack_protection (rtx base, HO
     }
 
   do_pending_stack_adjust ();
+  if (lab)
+    emit_label (lab);
 
   ret = get_insns ();
   end_sequence ();
--- gcc/asan.h.jj	2013-11-12 11:31:23.000000000 +0100
+++ gcc/asan.h	2013-11-14 15:42:57.371998293 +0100
@@ -23,7 +23,7 @@ along with GCC; see the file COPYING3.
 
 extern void asan_function_start (void);
 extern void asan_finish_file (void);
-extern rtx asan_emit_stack_protection (rtx, HOST_WIDE_INT *, tree *, int);
+extern rtx asan_emit_stack_protection (rtx, rtx, HOST_WIDE_INT *, tree *, int);
 extern bool asan_protect_global (tree);
 extern void initialize_sanitizer_builtins (void);
 
@@ -48,8 +48,10 @@ extern alias_set_type asan_shadow_set;
 #define ASAN_STACK_MAGIC_MIDDLE		0xf2
 #define ASAN_STACK_MAGIC_RIGHT		0xf3
 #define ASAN_STACK_MAGIC_PARTIAL	0xf4
+#define ASAN_STACK_MAGIC_USE_AFTER_RET	0xf5
 
-#define ASAN_STACK_FRAME_MAGIC	0x41b58ab3
+#define ASAN_STACK_FRAME_MAGIC		0x41b58ab3
+#define ASAN_STACK_RETIRED_MAGIC	0x45e0360e
 
 /* Return true if DECL should be guarded on the stack.  */
 


	Jakub


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