Implement protection of global variables

This patch implements the protection of global variables.  See the
comments appended to the beginning of the asan.c file.

	* varasm.c: Include asan.h.
	(assemble_noswitch_variable): Grow size by asan_red_zone_size
	if decl is asan protected.
	(place_block_symbol): Likewise.
	(assemble_variable): If decl is asan protected, increase
	DECL_ALIGN if needed, and for decls emitted using
	assemble_variable_contents append padding zeros after it.
	* Makefile.in (varasm.o): Depend on asan.h.
	* asan.c: Include output.h.
	(asan_pp, asan_pp_initialized, asan_ctor_statements): New variables.
	(asan_pp_initialize, asan_pp_string): New functions.
	(asan_emit_stack_protection): Use asan_pp{,_initialized}
	instead of local pp{,_initialized} vars, use asan_pp_initialize
	and asan_pp_string helpers.
	(asan_needs_local_alias, asan_protect_global,
	asan_global_struct, asan_add_global): New functions.
	(asan_finish_file): Protect global vars that can be protected. Use
	asan_ctor_statements instead of ctor_statements
	* asan.h (asan_protect_global): New prototype.
	(asan_red_zone_size): New inline function.

Co-Authored-By: Wei Mi <wmi@google.com>

From-SVN: r193437

gcc/ChangeLog

 2012-11-12  Jakub Jelinek  <jakub@redhat.com>
+	    Wei Mi <wmi@google.com>
+
+	* varasm.c: Include asan.h.
+	(assemble_noswitch_variable): Grow size by asan_red_zone_size
+	if decl is asan protected.
+	(place_block_symbol): Likewise.
+	(assemble_variable): If decl is asan protected, increase
+	DECL_ALIGN if needed, and for decls emitted using
+	assemble_variable_contents append padding zeros after it.
+	* Makefile.in (varasm.o): Depend on asan.h.
+	* asan.c: Include output.h.
+	(asan_pp, asan_pp_initialized, asan_ctor_statements): New variables.
+	(asan_pp_initialize, asan_pp_string): New functions.
+	(asan_emit_stack_protection): Use asan_pp{,_initialized}
+	instead of local pp{,_initialized} vars, use asan_pp_initialize
+	and asan_pp_string helpers.
+	(asan_needs_local_alias, asan_protect_global,
+	asan_global_struct, asan_add_global): New functions.
+	(asan_finish_file): Protect global vars that can be protected. Use
+	asan_ctor_statements instead of ctor_statements
+	* asan.h (asan_protect_global): New prototype.
+	(asan_red_zone_size): New inline function.
+
+2012-11-12  Jakub Jelinek  <jakub@redhat.com>
 
 	* Makefile.in (asan.o): Depend on $(EXPR_H) $(OPTABS_H).
 	(cfgexpand.o): Depend on asan.h.

gcc/Makefile.in

@@ -2719,7 +2719,7 @@ varasm.o : varasm.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(TREE_H) \
    output.h $(DIAGNOSTIC_CORE_H) xcoffout.h debug.h $(GGC_H) $(TM_P_H) \
    $(HASHTAB_H) $(TARGET_H) langhooks.h gt-varasm.h $(BASIC_BLOCK_H) \
    $(CGRAPH_H) $(TARGET_DEF_H) tree-mudflap.h \
-   pointer-set.h $(COMMON_TARGET_H)
+   pointer-set.h $(COMMON_TARGET_H) asan.h
 function.o : function.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(RTL_ERROR_H) \
    $(TREE_H) $(GIMPLE_H) $(FLAGS_H) $(FUNCTION_H) $(EXPR_H) \
    $(OPTABS_H) $(LIBFUNCS_H) $(REGS_H) hard-reg-set.h insn-config.h $(RECOG_H) \

gcc/asan.c

@@ -31,6 +31,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "target.h"
 #include "expr.h"
 #include "optabs.h"
+#include "output.h"
 
 /*
  AddressSanitizer finds out-of-bounds and use-after-free bugs 
@@ -166,7 +167,43 @@ along with GCC; see the file COPYING3.  If not see
  non-accessible) the regions of the red zones and mark the regions of
  stack variables as accessible, and emit some epilogue code to
  un-poison (mark as accessible) the regions of red zones right before
- the function exits.  */
+ the function exits.
+
+ [Protection of global variables]
+
+ The basic idea is to insert a red zone between two global variables
+ and install a constructor function that calls the asan runtime to do
+ the populating of the relevant shadow memory regions at load time.
+
+ So the global variables are laid out as to insert a red zone between
+ them. The size of the red zones is so that each variable starts on a
+ 32 bytes boundary.
+
+ Then a constructor function is installed so that, for each global
+ variable, it calls the runtime asan library function
+ __asan_register_globals_with an instance of this type:
+
+     struct __asan_global
+     {
+       // Address of the beginning of the global variable.
+       const void *__beg;
+
+       // Initial size of the global variable.
+       uptr __size;
+
+       // Size of the global variable + size of the red zone.  This
+       //   size is 32 bytes aligned.
+       uptr __size_with_redzone;
+
+       // Name of the global variable.
+       const void *__name;
+
+       // This is always set to NULL for now.
+       uptr __has_dynamic_init;
+     }
+
+ A destructor function that calls the runtime asan library function
+ _asan_unregister_globals is also installed.  */
 
 alias_set_type asan_shadow_set = -1;
 
@@ -174,6 +211,34 @@ alias_set_type asan_shadow_set = -1;
    alias set is used for all shadow memory accesses.  */
 static GTY(()) tree shadow_ptr_types[2];
 
+/* Asan pretty-printer, used for buidling of the description STRING_CSTs.  */
+static pretty_printer asan_pp;
+static bool asan_pp_initialized;
+
+/* Initialize asan_pp.  */
+
+static void
+asan_pp_initialize (void)
+{
+  pp_construct (&asan_pp, /* prefix */NULL, /* line-width */0);
+  asan_pp_initialized = true;
+}
+
+/* Create ADDR_EXPR of STRING_CST with asan_pp text.  */
+
+static tree
+asan_pp_string (void)
+{
+  const char *buf = pp_base_formatted_text (&asan_pp);
+  size_t len = strlen (buf);
+  tree ret = build_string (len + 1, buf);
+  TREE_TYPE (ret)
+    = build_array_type (char_type_node, build_index_type (size_int (len)));
+  TREE_READONLY (ret) = 1;
+  TREE_STATIC (ret) = 1;
+  return build1 (ADDR_EXPR, build_pointer_type (char_type_node), ret);
+}
+
 /* Return a CONST_INT representing 4 subsequent shadow memory bytes.  */
 
 static rtx
@@ -208,51 +273,38 @@ asan_emit_stack_protection (rtx base, HOST_WIDE_INT *offsets, tree *decls,
   HOST_WIDE_INT last_offset, last_size;
   int l;
   unsigned char cur_shadow_byte = ASAN_STACK_MAGIC_LEFT;
-  static pretty_printer pp;
-  static bool pp_initialized;
-  const char *buf;
-  size_t len;
   tree str_cst;
 
   /* First of all, prepare the description string.  */
-  if (!pp_initialized)
-    {
-      pp_construct (&pp, /* prefix */NULL, /* line-width */0);
-      pp_initialized = true;
-    }
-  pp_clear_output_area (&pp);
+  if (!asan_pp_initialized)
+    asan_pp_initialize ();
+
+  pp_clear_output_area (&asan_pp);
   if (DECL_NAME (current_function_decl))
-    pp_base_tree_identifier (&pp, DECL_NAME (current_function_decl));
+    pp_base_tree_identifier (&asan_pp, DECL_NAME (current_function_decl));
   else
-    pp_string (&pp, "<unknown>");
-  pp_space (&pp);
-  pp_decimal_int (&pp, length / 2 - 1);
-  pp_space (&pp);
+    pp_string (&asan_pp, "<unknown>");
+  pp_space (&asan_pp);
+  pp_decimal_int (&asan_pp, length / 2 - 1);
+  pp_space (&asan_pp);
   for (l = length - 2; l; l -= 2)
     {
       tree decl = decls[l / 2 - 1];
-      pp_wide_integer (&pp, offsets[l] - base_offset);
-      pp_space (&pp);
-      pp_wide_integer (&pp, offsets[l - 1] - offsets[l]);
-      pp_space (&pp);
+      pp_wide_integer (&asan_pp, offsets[l] - base_offset);
+      pp_space (&asan_pp);
+      pp_wide_integer (&asan_pp, offsets[l - 1] - offsets[l]);
+      pp_space (&asan_pp);
       if (DECL_P (decl) && DECL_NAME (decl))
 	{
-	  pp_decimal_int (&pp, IDENTIFIER_LENGTH (DECL_NAME (decl)));
-	  pp_space (&pp);
-	  pp_base_tree_identifier (&pp, DECL_NAME (decl));
+	  pp_decimal_int (&asan_pp, IDENTIFIER_LENGTH (DECL_NAME (decl)));
+	  pp_space (&asan_pp);
+	  pp_base_tree_identifier (&asan_pp, DECL_NAME (decl));
 	}
       else
-	pp_string (&pp, "9 <unknown>");
-      pp_space (&pp);
+	pp_string (&asan_pp, "9 <unknown>");
+      pp_space (&asan_pp);
     }
-  buf = pp_base_formatted_text (&pp);
-  len = strlen (buf);
-  str_cst = build_string (len + 1, buf);
-  TREE_TYPE (str_cst)
-    = build_array_type (char_type_node, build_index_type (size_int (len)));
-  TREE_READONLY (str_cst) = 1;
-  TREE_STATIC (str_cst) = 1;
-  str_cst = build1 (ADDR_EXPR, build_pointer_type (char_type_node), str_cst);
+  str_cst = asan_pp_string ();
 
   /* Emit the prologue sequence.  */
   base = expand_binop (Pmode, add_optab, base, GEN_INT (base_offset),
@@ -357,6 +409,75 @@ asan_emit_stack_protection (rtx base, HOST_WIDE_INT *offsets, tree *decls,
   return ret;
 }
 
+/* Return true if DECL, a global var, might be overridden and needs
+   therefore a local alias.  */
+
+static bool
+asan_needs_local_alias (tree decl)
+{
+  return DECL_WEAK (decl) || !targetm.binds_local_p (decl);
+}
+
+/* Return true if DECL is a VAR_DECL that should be protected
+   by Address Sanitizer, by appending a red zone with protected
+   shadow memory after it and aligning it to at least
+   ASAN_RED_ZONE_SIZE bytes.  */
+
+bool
+asan_protect_global (tree decl)
+{
+  rtx rtl, symbol;
+  section *sect;
+
+  if (TREE_CODE (decl) != VAR_DECL
+      /* TLS vars aren't statically protectable.  */
+      || DECL_THREAD_LOCAL_P (decl)
+      /* Externs will be protected elsewhere.  */
+      || DECL_EXTERNAL (decl)
+      || !TREE_ASM_WRITTEN (decl)
+      || !DECL_RTL_SET_P (decl)
+      /* Comdat vars pose an ABI problem, we can't know if
+	 the var that is selected by the linker will have
+	 padding or not.  */
+      || DECL_ONE_ONLY (decl)
+      /* Similarly for common vars.  People can use -fno-common.  */
+      || DECL_COMMON (decl)
+      /* Don't protect if using user section, often vars placed
+	 into user section from multiple TUs are then assumed
+	 to be an array of such vars, putting padding in there
+	 breaks this assumption.  */
+      || (DECL_SECTION_NAME (decl) != NULL_TREE
+	  && !DECL_HAS_IMPLICIT_SECTION_NAME_P (decl))
+      || DECL_SIZE (decl) == 0
+      || ASAN_RED_ZONE_SIZE * BITS_PER_UNIT > MAX_OFILE_ALIGNMENT
+      || !valid_constant_size_p (DECL_SIZE_UNIT (decl))
+      || DECL_ALIGN_UNIT (decl) > 2 * ASAN_RED_ZONE_SIZE)
+    return false;
+
+  rtl = DECL_RTL (decl);
+  if (!MEM_P (rtl) || GET_CODE (XEXP (rtl, 0)) != SYMBOL_REF)
+    return false;
+  symbol = XEXP (rtl, 0);
+
+  if (CONSTANT_POOL_ADDRESS_P (symbol)
+      || TREE_CONSTANT_POOL_ADDRESS_P (symbol))
+    return false;
+
+  sect = get_variable_section (decl, false);
+  if (sect->common.flags & SECTION_COMMON)
+    return false;
+
+  if (lookup_attribute ("weakref", DECL_ATTRIBUTES (decl)))
+    return false;
+
+#ifndef ASM_OUTPUT_DEF
+  if (asan_needs_local_alias (decl))
+    return false;
+#endif
+
+  return true;    
+}
+
 /* Construct a function tree for __asan_report_{load,store}{1,2,4,8,16}.
    IS_STORE is either 1 (for a store) or 0 (for a load).
    SIZE_IN_BYTES is one of 1, 2, 4, 8, 16.  */
@@ -657,6 +778,105 @@ transform_statements (void)
     }
 }
 
+/* Build
+   struct __asan_global
+   {
+     const void *__beg;
+     uptr __size;
+     uptr __size_with_redzone;
+     const void *__name;
+     uptr __has_dynamic_init;
+   } type.  */
+
+static tree
+asan_global_struct (void)
+{
+  static const char *field_names[5]
+    = { "__beg", "__size", "__size_with_redzone",
+	"__name", "__has_dynamic_init" };
+  tree fields[5], ret;
+  int i;
+
+  ret = make_node (RECORD_TYPE);
+  for (i = 0; i < 5; i++)
+    {
+      fields[i]
+	= build_decl (UNKNOWN_LOCATION, FIELD_DECL,
+		      get_identifier (field_names[i]),
+		      (i == 0 || i == 3) ? const_ptr_type_node
+		      : build_nonstandard_integer_type (POINTER_SIZE, 1));
+      DECL_CONTEXT (fields[i]) = ret;
+      if (i)
+	DECL_CHAIN (fields[i - 1]) = fields[i];
+    }
+  TYPE_FIELDS (ret) = fields[0];
+  TYPE_NAME (ret) = get_identifier ("__asan_global");
+  layout_type (ret);
+  return ret;
+}
+
+/* Append description of a single global DECL into vector V.
+   TYPE is __asan_global struct type as returned by asan_global_struct.  */
+
+static void
+asan_add_global (tree decl, tree type, VEC(constructor_elt, gc) *v)
+{
+  tree init, uptr = TREE_TYPE (DECL_CHAIN (TYPE_FIELDS (type)));
+  unsigned HOST_WIDE_INT size;
+  tree str_cst, refdecl = decl;
+  VEC(constructor_elt, gc) *vinner = NULL;
+
+  if (!asan_pp_initialized)
+    asan_pp_initialize ();
+
+  pp_clear_output_area (&asan_pp);
+  if (DECL_NAME (decl))
+    pp_base_tree_identifier (&asan_pp, DECL_NAME (decl));
+  else
+    pp_string (&asan_pp, "<unknown>");
+  pp_space (&asan_pp);
+  pp_left_paren (&asan_pp);
+  pp_string (&asan_pp, main_input_filename);
+  pp_right_paren (&asan_pp);
+  str_cst = asan_pp_string ();
+
+  if (asan_needs_local_alias (decl))
+    {
+      char buf[20];
+      ASM_GENERATE_INTERNAL_LABEL (buf, "LASAN",
+				   VEC_length (constructor_elt, v) + 1);
+      refdecl = build_decl (DECL_SOURCE_LOCATION (decl),
+			    VAR_DECL, get_identifier (buf), TREE_TYPE (decl));
+      TREE_ADDRESSABLE (refdecl) = TREE_ADDRESSABLE (decl);
+      TREE_READONLY (refdecl) = TREE_READONLY (decl);
+      TREE_THIS_VOLATILE (refdecl) = TREE_THIS_VOLATILE (decl);
+      DECL_GIMPLE_REG_P (refdecl) = DECL_GIMPLE_REG_P (decl);
+      DECL_ARTIFICIAL (refdecl) = DECL_ARTIFICIAL (decl);
+      DECL_IGNORED_P (refdecl) = DECL_IGNORED_P (decl);
+      TREE_STATIC (refdecl) = 1;
+      TREE_PUBLIC (refdecl) = 0;
+      TREE_USED (refdecl) = 1;
+      assemble_alias (refdecl, DECL_ASSEMBLER_NAME (decl));
+    }
+
+  CONSTRUCTOR_APPEND_ELT (vinner, NULL_TREE,
+			  fold_convert (const_ptr_type_node,
+					build_fold_addr_expr (refdecl)));
+  size = tree_low_cst (DECL_SIZE_UNIT (decl), 1);
+  CONSTRUCTOR_APPEND_ELT (vinner, NULL_TREE, build_int_cst (uptr, size));
+  size += asan_red_zone_size (size);
+  CONSTRUCTOR_APPEND_ELT (vinner, NULL_TREE, build_int_cst (uptr, size));
+  CONSTRUCTOR_APPEND_ELT (vinner, NULL_TREE,
+			  fold_convert (const_ptr_type_node, str_cst));
+  CONSTRUCTOR_APPEND_ELT (vinner, NULL_TREE, build_int_cst (uptr, 0));
+  init = build_constructor (type, vinner);
+  CONSTRUCTOR_APPEND_ELT (v, NULL_TREE, init);
+}
+
+/* Needs to be GTY(()), because cgraph_build_static_cdtor may
+   invoke ggc_collect.  */
+static GTY(()) tree asan_ctor_statements;
+
 /* Module-level instrumentation.
    - Insert __asan_init() into the list of CTORs.
    - TODO: insert redzones around globals.
@@ -665,11 +885,61 @@ transform_statements (void)
 void
 asan_finish_file (void)
 {
-  tree ctor_statements = NULL_TREE;
+  struct varpool_node *vnode;
+  unsigned HOST_WIDE_INT gcount = 0;
+
   append_to_statement_list (build_call_expr (asan_init_func (), 0),
-                            &ctor_statements);
-  cgraph_build_static_cdtor ('I', ctor_statements,
-                             MAX_RESERVED_INIT_PRIORITY - 1);
+			    &asan_ctor_statements);
+  FOR_EACH_DEFINED_VARIABLE (vnode)
+    if (asan_protect_global (vnode->symbol.decl))
+      ++gcount;
+  if (gcount)
+    {
+      tree type = asan_global_struct (), var, ctor, decl;
+      tree uptr = build_nonstandard_integer_type (POINTER_SIZE, 1);
+      tree dtor_statements = NULL_TREE;
+      VEC(constructor_elt, gc) *v;
+      char buf[20];
+
+      type = build_array_type_nelts (type, gcount);
+      ASM_GENERATE_INTERNAL_LABEL (buf, "LASAN", 0);
+      var = build_decl (UNKNOWN_LOCATION, VAR_DECL, get_identifier (buf),
+			type);
+      TREE_STATIC (var) = 1;
+      TREE_PUBLIC (var) = 0;
+      DECL_ARTIFICIAL (var) = 1;
+      DECL_IGNORED_P (var) = 1;
+      v = VEC_alloc (constructor_elt, gc, gcount);
+      FOR_EACH_DEFINED_VARIABLE (vnode)
+	if (asan_protect_global (vnode->symbol.decl))
+	  asan_add_global (vnode->symbol.decl, TREE_TYPE (type), v);
+      ctor = build_constructor (type, v);
+      TREE_CONSTANT (ctor) = 1;
+      TREE_STATIC (ctor) = 1;
+      DECL_INITIAL (var) = ctor;
+      varpool_assemble_decl (varpool_node_for_decl (var));
+
+      type = build_function_type_list (void_type_node,
+				       build_pointer_type (TREE_TYPE (type)),
+				       uptr, NULL_TREE);
+      decl = build_fn_decl ("__asan_register_globals", type);
+      TREE_NOTHROW (decl) = 1;
+      append_to_statement_list (build_call_expr (decl, 2,
+						 build_fold_addr_expr (var),
+						 build_int_cst (uptr, gcount)),
+				&asan_ctor_statements);
+
+      decl = build_fn_decl ("__asan_unregister_globals", type);
+      TREE_NOTHROW (decl) = 1;
+      append_to_statement_list (build_call_expr (decl, 2,
+						 build_fold_addr_expr (var),
+						 build_int_cst (uptr, gcount)),
+				&dtor_statements);
+      cgraph_build_static_cdtor ('D', dtor_statements,
+				 MAX_RESERVED_INIT_PRIORITY - 1);
+    }
+  cgraph_build_static_cdtor ('I', asan_ctor_statements,
+			     MAX_RESERVED_INIT_PRIORITY - 1);
 }
 
 /* Initialize shadow_ptr_types array.  */

gcc/asan.h

@@ -23,6 +23,7 @@ along with GCC; see the file COPYING3.  If not see
 
 extern void asan_finish_file (void);
 extern rtx asan_emit_stack_protection (rtx, HOST_WIDE_INT *, tree *, int);
+extern bool asan_protect_global (tree);
 
 /* Alias set for accessing the shadow memory.  */
 extern alias_set_type asan_shadow_set;
@@ -56,4 +57,14 @@ asan_protect_stack_decl (tree decl)
   return DECL_P (decl) && !DECL_ARTIFICIAL (decl);
 }
 
+/* Return the size of padding needed to insert after a protected
+   decl of SIZE.  */
+
+static inline unsigned int
+asan_red_zone_size (unsigned int size)
+{
+  unsigned int c = size & (ASAN_RED_ZONE_SIZE - 1);
+  return c ? 2 * ASAN_RED_ZONE_SIZE - c : ASAN_RED_ZONE_SIZE;
+}
+
 #endif /* TREE_ASAN */

gcc/varasm.c

@@ -51,6 +51,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-mudflap.h"
 #include "cgraph.h"
 #include "pointer-set.h"
+#include "asan.h"
 
 #ifdef XCOFF_DEBUGGING_INFO
 #include "xcoffout.h"		/* Needed for external data
@@ -1831,6 +1832,9 @@ assemble_noswitch_variable (tree decl, const char *name, section *sect)
   size = tree_low_cst (DECL_SIZE_UNIT (decl), 1);
   rounded = size;
 
+  if (flag_asan && asan_protect_global (decl))
+    size += asan_red_zone_size (size);
+
   /* Don't allocate zero bytes of common,
      since that means "undefined external" in the linker.  */
   if (size == 0)
@@ -1897,6 +1901,7 @@ assemble_variable (tree decl, int top_level ATTRIBUTE_UNUSED,
   const char *name;
   rtx decl_rtl, symbol;
   section *sect;
+  bool asan_protected = false;
 
   /* This function is supposed to handle VARIABLES.  Ensure we have one.  */
   gcc_assert (TREE_CODE (decl) == VAR_DECL);
@@ -1984,6 +1989,15 @@ assemble_variable (tree decl, int top_level ATTRIBUTE_UNUSED,
   /* Compute the alignment of this data.  */
 
   align_variable (decl, dont_output_data);
+
+  if (flag_asan
+      && asan_protect_global (decl))
+    {
+      asan_protected = true;
+      DECL_ALIGN (decl) = MAX (DECL_ALIGN (decl), 
+                               ASAN_RED_ZONE_SIZE * BITS_PER_UNIT);
+    }
+
   set_mem_align (decl_rtl, DECL_ALIGN (decl));
 
   if (TREE_PUBLIC (decl))
@@ -2022,6 +2036,12 @@ assemble_variable (tree decl, int top_level ATTRIBUTE_UNUSED,
       if (DECL_ALIGN (decl) > BITS_PER_UNIT)
 	ASM_OUTPUT_ALIGN (asm_out_file, floor_log2 (DECL_ALIGN_UNIT (decl)));
       assemble_variable_contents (decl, name, dont_output_data);
+      if (asan_protected)
+	{
+	  unsigned HOST_WIDE_INT int size
+	    = tree_low_cst (DECL_SIZE_UNIT (decl), 1);
+	  assemble_zeros (asan_red_zone_size (size));
+	}
     }
 }
 
@@ -6926,6 +6946,8 @@ place_block_symbol (rtx symbol)
       decl = SYMBOL_REF_DECL (symbol);
       alignment = DECL_ALIGN (decl);
       size = tree_low_cst (DECL_SIZE_UNIT (decl), 1);
+      if (flag_asan && asan_protect_global (decl))
+	size += asan_red_zone_size (size);
     }
 
   /* Calculate the object's offset from the start of the block.  */