-fstack-protector-strong: Instrumentation for return slots

This patch fixes a loophole in the -fstack-protector-strong protection.
If a function call uses a return slot, the caller needs stack protector
instrumentation because the return slot is addressable. 

gcc/

2014-05-09  Florian Weimer  <fweimer@redhat.com>

	* cfgexpand.c (stack_protect_decl_p): New function, extracted from
	expand_used_vars.
	(stack_protect_return_slot_p): New function.
	(expand_used_vars): Call stack_protect_decl_p and
	stack_protect_return_slot_p for -fstack-protector-strong.

gcc/testsuite/

2014-05-09  Florian Weimer  <fweimer@redhat.com>

	* gcc.dg/fstack-protector-strong.c: Add coverage for return slots.
	* g++.dg/fstack-protector-strong.C: Likewise.
	* gcc.target/i386/ssp-strong-reg.c: New file.

From-SVN: r210275

6 files changed, 149 insertions, 18 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ffe31f3..6b508f7 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2014-05-09  Florian Weimer  <fweimer@redhat.com>
+
+	* cfgexpand.c (stack_protect_decl_p): New function, extracted from
+	expand_used_vars.
+	(stack_protect_return_slot_p): New function.
+	(expand_used_vars): Call stack_protect_decl_p and
+	stack_protect_return_slot_p for -fstack-protector-strong.
+
 2014-05-06  Kenneth Zadeck  <zadeck@naturalbridge.com>
 
 	PR middle-end/61111
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index b57fac1..934f40d 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -1611,6 +1611,52 @@ record_or_union_type_has_array_p (const_tree tree_type)
   return 0;
 }
 
+/* Check if the current function has local referenced variables that
+   have their addresses taken, contain an array, or are arrays.  */
+
+static bool
+stack_protect_decl_p ()
+{
+  unsigned i;
+  tree var;
+
+  FOR_EACH_LOCAL_DECL (cfun, i, var)
+    if (!is_global_var (var))
+      {
+	tree var_type = TREE_TYPE (var);
+	if (TREE_CODE (var) == VAR_DECL
+	    && (TREE_CODE (var_type) == ARRAY_TYPE
+		|| TREE_ADDRESSABLE (var)
+		|| (RECORD_OR_UNION_TYPE_P (var_type)
+		    && record_or_union_type_has_array_p (var_type))))
+	  return true;
+      }
+  return false;
+}
+
+/* Check if the current function has calls that use a return slot.  */
+
+static bool
+stack_protect_return_slot_p ()
+{
+  basic_block bb;
+  
+  FOR_ALL_BB_FN (bb, cfun)
+    for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
+	 !gsi_end_p (gsi); gsi_next (&gsi))
+      {
+	gimple stmt = gsi_stmt (gsi);
+	/* This assumes that calls to internal-only functions never
+	   use a return slot.  */
+	if (is_gimple_call (stmt)
+	    && !gimple_call_internal_p (stmt)
+	    && aggregate_value_p (TREE_TYPE (gimple_call_fntype (stmt)),
+				  gimple_call_fndecl (stmt)))
+	  return true;
+      }
+  return false;
+}
+
 /* Expand all variables used in the function.  */
 
 static rtx
@@ -1683,22 +1729,8 @@ expand_used_vars (void)
   pointer_map_destroy (ssa_name_decls);
 
   if (flag_stack_protect == SPCT_FLAG_STRONG)
-    FOR_EACH_LOCAL_DECL (cfun, i, var)
-      if (!is_global_var (var))
-	{
-	  tree var_type = TREE_TYPE (var);
-	  /* Examine local referenced variables that have their addresses taken,
-	     contain an array, or are arrays.  */
-	  if (TREE_CODE (var) == VAR_DECL
-	      && (TREE_CODE (var_type) == ARRAY_TYPE
-		  || TREE_ADDRESSABLE (var)
-		  || (RECORD_OR_UNION_TYPE_P (var_type)
-		      && record_or_union_type_has_array_p (var_type))))
-	    {
-	      gen_stack_protect_signal = true;
-	      break;
-	    }
-	}
+      gen_stack_protect_signal
+	= stack_protect_decl_p () || stack_protect_return_slot_p ();
 
   /* At this point all variables on the local_decls with TREE_USED
      set are not associated with any block scope.  Lay them out.  */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 8918976..9092cba 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2014-05-09  Florian Weimer  <fweimer@redhat.com>
+
+	* gcc.dg/fstack-protector-strong.c: Add coverage for return slots.
+	* g++.dg/fstack-protector-strong.C: Likewise.
+	* gcc.target/i386/ssp-strong-reg.c: New file.
+
 2014-05-09  Georg-Johann Lay  <avr@gjlay.de>
 
 	PR target/61055
diff --git a/gcc/testsuite/g++.dg/fstack-protector-strong.C b/gcc/testsuite/g++.dg/fstack-protector-strong.C
index a4f0f81..5a820ed 100644
--- a/gcc/testsuite/g++.dg/fstack-protector-strong.C
+++ b/gcc/testsuite/g++.dg/fstack-protector-strong.C
@@ -32,4 +32,52 @@ int foo2 ()
   return global_func (a);
 }
 
-/* { dg-final { scan-assembler-times "stack_chk_fail" 2 } } */
+/* Frame addressed exposed through return slot. */
+
+struct B
+{
+  /* Discourage passing this struct in registers. */
+  int a1, a2, a3, a4, a5, a6, a7, a8, a9, a10;
+  int method ();
+  B return_slot();
+};
+
+B global_func ();
+void noop ();
+
+int foo3 ()
+{
+  return global_func ().a1;
+}
+
+int foo4 ()
+{
+  try {
+    noop ();
+    return 0;
+  } catch (...) {
+    return global_func ().a1;
+  }
+}
+
+int foo5 ()
+{
+  try {
+    return global_func ().a1;
+  } catch (...) {
+    return 0;
+  }
+}
+
+int foo6 ()
+{
+  B b;
+  return b.method ();
+}
+
+int foo7 (B *p)
+{
+  return p->return_slot ().a1;
+}
+
+/* { dg-final { scan-assembler-times "stack_chk_fail" 7 } } */
diff --git a/gcc/testsuite/gcc.dg/fstack-protector-strong.c b/gcc/testsuite/gcc.dg/fstack-protector-strong.c
index 7c232ff..da33abb 100644
--- a/gcc/testsuite/gcc.dg/fstack-protector-strong.c
+++ b/gcc/testsuite/gcc.dg/fstack-protector-strong.c
@@ -131,4 +131,22 @@ foo10 ()
   return bb.three;
 }
 
-/* { dg-final { scan-assembler-times "stack_chk_fail" 10 } } */
+struct B
+{
+  /* Discourage passing this struct in registers. */
+  int a1, a2, a3, a4, a5, a6, a7, a8, a9, a10;
+};
+
+struct B global3 (void);
+
+int foo11 ()
+{
+  return global3 ().a1;
+}
+
+void foo12 ()
+{
+  global3 ();
+}
+
+/* { dg-final { scan-assembler-times "stack_chk_fail" 12 } } */
diff --git a/gcc/testsuite/gcc.target/i386/ssp-strong-reg.c b/gcc/testsuite/gcc.target/i386/ssp-strong-reg.c
new file mode 100644
index 0000000..9fe5664
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/ssp-strong-reg.c
@@ -0,0 +1,19 @@
+/* Test that structs returned in registers do not lead to
+   instrumentation with -fstack-protector-strong.  */
+
+/* { dg-do compile { target { ! { ia32 } } } } */
+/* { dg-options "-O2 -fstack-protector-strong" } */
+
+struct S {
+  int a;
+  int b;
+};
+
+struct S f (void);
+
+int g (void)
+{
+  return f ().a;
+}
+
+/* { dg-final { scan-assembler-times "stack_chk_fail" 0 } } */