Re: [PATCH][ubsan] Add VLA bound instrumentation

[Marek Polacek <polacek at redhat dot com>]

On Fri, Nov 01, 2013 at 01:35:07PM -0400, Jason Merrill wrote:
> On 10/31/2013 02:28 PM, Marek Polacek wrote:
> >  	  /* A variable sized array.  */
> >  	  itype = variable_size (itype);
> >+
> >+	  /* We need to stabilize side-effects in VLA sizes for regular array
> >+	     declarations too, not just pointers to arrays.  */
> >+	  stabilize_vla_size (itype);
> 
> Let's put this after the later call to variable_size, too.
> 
> >  	  if (TREE_CODE (itype) != SAVE_EXPR)
> >  	    {
> >  	      /* Look for SIZEOF_EXPRs in itype and fold them, otherwise
> >@@ -8390,6 +8385,31 @@ compute_array_index_type (tree name, tre
> >  	      if (found)
> >  		itype = variable_size (fold (newitype));
> >  	    }
> 
> i.e. here.

Done.
 
> >+
> >+	  if (cxx_dialect >= cxx1y)
> >+	    {
> >+	      /* If the VLA bound is larger than half the address space,
> >+	         or less than zero, throw std::bad_array_length.  */
> >+	      tree comp = build2 (LT_EXPR, boolean_type_node, itype,
> >+				  ssize_int (-1));
> >+	      comp = build3 (COND_EXPR, void_type_node, comp,
> >+			     throw_bad_array_length (), void_zero_node);
> >+	      finish_expr_stmt (comp);
> >+	  }
> >+
> >+         if ((flag_sanitize & SANITIZE_VLA)
> >+             /* From C++1y onwards, we throw an exception on a negative
> >+                length size of an array; see above  */
> >+             && cxx_dialect < cxx1y)
> 
> This could be
> 
>   else if (flag_sanitize & SANITIZE_VLA)

Done (with some formatting nits fixed).

> There's another use of stabilize_vla_size in grokdeclarator, that
> should be able to go as well.

Yep, seems so.  

Regtest/bootstrap on x86_64-linux running (so far lookin' good), ok if passes?

2013-11-01  Marek Polacek  <polacek@redhat.com>

	Implement -fsanitize=vla-bound.
	* opts.c (common_handle_option): Handle vla-bound.
	* sanitizer.def (BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE):
	Define.
	* flag-types.h (enum sanitize_code): Add SANITIZE_VLA.
	* asan.c (initialize_sanitizer_builtins): Build BT_FN_VOID_PTR_PTR.
c-family/
	* c-ubsan.c: Don't include hash-table.h.
	(ubsan_instrument_vla): New function.
	* c-ubsan.h: Declare it.
cp/
	* decl.c (cp_finish_decl): Move C++1y bounds checking...
	(compute_array_index_type): ...here.  Add VLA instrumentation.
	Call stabilize_vla_size.
	(grokdeclarator): Don't call stabilize_vla_size here.
c/
	* c-decl.c (grokdeclarator): Add VLA instrumentation.
testsuite/
	* g++.dg/ubsan/cxx1y-vla.C: New test.
	* c-c++-common/ubsan/vla-3.c: New test.
	* c-c++-common/ubsan/vla-2.c: New test.
	* c-c++-common/ubsan/vla-4.c: New test.
	* c-c++-common/ubsan/vla-1.c: New test.

--- gcc/opts.c.mp	2013-11-01 18:53:17.372014692 +0100
+++ gcc/opts.c	2013-11-01 18:53:48.857130430 +0100
@@ -1444,6 +1444,7 @@ common_handle_option (struct gcc_options
 	      { "undefined", SANITIZE_UNDEFINED, sizeof "undefined" - 1 },
 	      { "unreachable", SANITIZE_UNREACHABLE,
 		sizeof "unreachable" - 1 },
+	      { "vla-bound", SANITIZE_VLA, sizeof "vla-bound" - 1 },
 	      { NULL, 0, 0 }
 	    };
 	    const char *comma;
--- gcc/c-family/c-ubsan.c.mp	2013-11-01 18:53:17.389014762 +0100
+++ gcc/c-family/c-ubsan.c	2013-11-01 18:53:48.858130434 +0100
@@ -25,7 +25,6 @@ along with GCC; see the file COPYING3.
 #include "alloc-pool.h"
 #include "cgraph.h"
 #include "gimple.h"
-#include "hash-table.h"
 #include "output.h"
 #include "toplev.h"
 #include "ubsan.h"
@@ -86,8 +85,7 @@ ubsan_instrument_division (location_t lo
   return t;
 }
 
-/* Instrument left and right shifts.  If not instrumenting, return
-   NULL_TREE.  */
+/* Instrument left and right shifts.  */
 
 tree
 ubsan_instrument_shift (location_t loc, enum tree_code code,
@@ -157,4 +155,23 @@ ubsan_instrument_shift (location_t loc,
   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_zero_node);
 
   return t;
+}
+
+/* Instrument variable length array bound.  */
+
+tree
+ubsan_instrument_vla (location_t loc, tree size)
+{
+  tree type = TREE_TYPE (size);
+  tree t, tt;
+
+  t = fold_build2 (LE_EXPR, boolean_type_node, size, build_int_cst (type, 0));
+  tree data = ubsan_create_data ("__ubsan_vla_data",
+				 loc, ubsan_type_descriptor (type), NULL_TREE);
+  data = build_fold_addr_expr_loc (loc, data);
+  tt = builtin_decl_explicit (BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE);
+  tt = build_call_expr_loc (loc, tt, 2, data, ubsan_encode_value (size));
+  t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_zero_node);
+
+  return t;
 }
--- gcc/c-family/c-ubsan.h.mp	2013-11-01 18:53:17.395014787 +0100
+++ gcc/c-family/c-ubsan.h	2013-11-01 18:53:48.864130461 +0100
@@ -23,5 +23,6 @@ along with GCC; see the file COPYING3.
 
 extern tree ubsan_instrument_division (location_t, tree, tree);
 extern tree ubsan_instrument_shift (location_t, enum tree_code, tree, tree);
+extern tree ubsan_instrument_vla (location_t, tree);
 
 #endif  /* GCC_C_UBSAN_H  */
--- gcc/sanitizer.def.mp	2013-11-01 18:53:17.403014823 +0100
+++ gcc/sanitizer.def	2013-11-01 18:53:48.865130465 +0100
@@ -297,3 +297,7 @@ DEF_SANITIZER_BUILTIN(BUILT_IN_UBSAN_HAN
 		      "__ubsan_handle_builtin_unreachable",
 		      BT_FN_VOID_PTR,
 		      ATTR_COLD_NORETURN_NOTHROW_LEAF_LIST)
+DEF_SANITIZER_BUILTIN(BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE,
+		      "__ubsan_handle_vla_bound_not_positive",
+		      BT_FN_VOID_PTR_PTR,
+		      ATTR_COLD_NOTHROW_LEAF_LIST)
--- gcc/flag-types.h.mp	2013-11-01 18:53:17.405014831 +0100
+++ gcc/flag-types.h	2013-11-01 18:53:48.866130469 +0100
@@ -210,7 +210,9 @@ enum sanitize_code {
   SANITIZE_SHIFT = 1 << 2,
   SANITIZE_DIVIDE = 1 << 3,
   SANITIZE_UNREACHABLE = 1 << 4,
+  SANITIZE_VLA = 1 << 5,
   SANITIZE_UNDEFINED = SANITIZE_SHIFT | SANITIZE_DIVIDE | SANITIZE_UNREACHABLE
+		       | SANITIZE_VLA
 };
 
 /* flag_vtable_verify initialization levels. */
--- gcc/cp/decl.c.mp	2013-11-01 18:53:17.425014915 +0100
+++ gcc/cp/decl.c	2013-11-01 19:44:46.897799049 +0100
@@ -45,6 +45,7 @@ along with GCC; see the file COPYING3.
 #include "c-family/c-objc.h"
 #include "c-family/c-pragma.h"
 #include "c-family/c-target.h"
+#include "c-family/c-ubsan.h"
 #include "diagnostic.h"
 #include "intl.h"
 #include "debug.h"
@@ -6399,17 +6400,6 @@ cp_finish_decl (tree decl, tree init, bo
 	   && TYPE_FOR_JAVA (type) && MAYBE_CLASS_TYPE_P (type))
     error ("non-static data member %qD has Java class type", decl);
 
-  if (cxx_dialect >= cxx1y && array_of_runtime_bound_p (type))
-    {
-      /* If the VLA bound is larger than half the address space, or less
-	 than zero, throw std::bad_array_length.  */
-      tree max = convert (ssizetype, TYPE_MAX_VALUE (TYPE_DOMAIN (type)));
-      tree comp = build2 (LT_EXPR, boolean_type_node, max, ssize_int (-1));
-      comp = build3 (COND_EXPR, void_type_node, comp,
-		     throw_bad_array_length (), void_zero_node);
-      finish_expr_stmt (comp);
-    }
-
   /* Add this declaration to the statement-tree.  This needs to happen
      after the call to check_initializer so that the DECL_EXPR for a
      reference temp is added before the DECL_EXPR for the reference itself.  */
@@ -8379,6 +8369,7 @@ compute_array_index_type (tree name, tre
 	{
 	  /* A variable sized array.  */
 	  itype = variable_size (itype);
+
 	  if (TREE_CODE (itype) != SAVE_EXPR)
 	    {
 	      /* Look for SIZEOF_EXPRs in itype and fold them, otherwise
@@ -8390,6 +8381,34 @@ compute_array_index_type (tree name, tre
 	      if (found)
 		itype = variable_size (fold (newitype));
 	    }
+
+	  /* We need to stabilize side-effects in VLA sizes for regular array
+	     declarations too, not just pointers to arrays.  */
+	  stabilize_vla_size (itype);
+
+	  if (cxx_dialect >= cxx1y)
+	    {
+	      /* If the VLA bound is larger than half the address space,
+	         or less than zero, throw std::bad_array_length.  */
+	      tree comp = build2 (LT_EXPR, boolean_type_node, itype,
+				  ssize_int (-1));
+	      comp = build3 (COND_EXPR, void_type_node, comp,
+			     throw_bad_array_length (), void_zero_node);
+	      finish_expr_stmt (comp);
+	    }
+	  else if (flag_sanitize & SANITIZE_VLA)
+	    {
+	      /* From C++1y onwards, we throw an exception on a negative
+		 length size of an array; see above.  */
+
+	      /* We have to add 1 -- in the ubsan routine we generate
+		 LE_EXPR rather than LT_EXPR.  */
+	      tree t = fold_build2 (PLUS_EXPR, TREE_TYPE (itype), itype,
+				    build_one_cst (TREE_TYPE (itype)));
+	      t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t),
+			       ubsan_instrument_vla (input_location, t), t);
+	      finish_expr_stmt (t);
+	    }
 	}
       /* Make sure that there was no overflow when creating to a signed
 	 index type.  (For example, on a 32-bit machine, an array with
@@ -9790,12 +9809,8 @@ grokdeclarator (const cp_declarator *dec
 	      && (decl_context == NORMAL || decl_context == FIELD)
 	      && at_function_scope_p ()
 	      && variably_modified_type_p (type, NULL_TREE))
-	    {
-	      /* First break out any side-effects.  */
-	      stabilize_vla_size (TYPE_SIZE (type));
-	      /* And then force evaluation of the SAVE_EXPR.  */
-	      finish_expr_stmt (TYPE_SIZE (type));
-	    }
+	    /* Force evaluation of the SAVE_EXPR.  */
+	    finish_expr_stmt (TYPE_SIZE (type));
 
 	  if (declarator->kind == cdk_reference)
 	    {
@@ -9886,14 +9901,6 @@ grokdeclarator (const cp_declarator *dec
 	}
     }
 
-  /* We need to stabilize side-effects in VLA sizes for regular array
-     declarations too, not just pointers to arrays.  */
-  if (type != error_mark_node && !TYPE_NAME (type)
-      && (decl_context == NORMAL || decl_context == FIELD)
-      && at_function_scope_p ()
-      && variably_modified_type_p (type, NULL_TREE))
-    stabilize_vla_size (TYPE_SIZE (type));
-
   /* A `constexpr' specifier used in an object declaration declares
      the object as `const'.  */
   if (constexpr_p && innermost_code != cdk_function)
--- gcc/c/c-decl.c.mp	2013-11-01 18:53:17.443014991 +0100
+++ gcc/c/c-decl.c	2013-11-01 18:53:48.946130794 +0100
@@ -45,6 +45,7 @@ along with GCC; see the file COPYING3.
 #include "c-family/c-common.h"
 #include "c-family/c-objc.h"
 #include "c-family/c-pragma.h"
+#include "c-family/c-ubsan.h"
 #include "c-lang.h"
 #include "langhooks.h"
 #include "tree-iterator.h"
@@ -5411,6 +5412,16 @@ grokdeclarator (const struct c_declarato
 		       with known value.  */
 		    this_size_varies = size_varies = true;
 		    warn_variable_length_array (name, size);
+		    if (flag_sanitize & SANITIZE_VLA
+		        && decl_context == NORMAL)
+		      {
+			/* Evaluate the array size only once.  */
+			size = c_save_expr (size);
+			size = c_fully_fold (size, false, NULL);
+		        size = fold_build2 (COMPOUND_EXPR, TREE_TYPE (size),
+					    ubsan_instrument_vla (loc, size),
+					    size);
+		      }
 		  }
 
 		if (integer_zerop (size) && !this_size_varies)
--- gcc/testsuite/g++.dg/ubsan/cxx1y-vla.C.mp	2013-11-01 18:53:55.957155884 +0100
+++ gcc/testsuite/g++.dg/ubsan/cxx1y-vla.C	2013-11-01 18:53:48.956130834 +0100
@@ -0,0 +1,13 @@
+/* { dg-do run } */
+/* { dg-options "-fsanitize=vla-bound -w -std=c++1y" } */
+/* { dg-shouldfail "ubsan" } */
+
+int
+main (void)
+{
+  int y = -18;
+  int a[y];
+  return 0;
+}
+
+/* { dg-output "terminate called after throwing an instance" } */
--- gcc/testsuite/c-c++-common/ubsan/vla-3.c.mp	2013-11-01 18:54:05.024188578 +0100
+++ gcc/testsuite/c-c++-common/ubsan/vla-3.c	2013-11-01 18:53:48.957130838 +0100
@@ -0,0 +1,16 @@
+/* { dg-do run } */
+/* { dg-options "-fsanitize=vla-bound -w" } */
+
+/* Don't instrument the arrays here.  */
+int
+foo (int n, int a[])
+{
+  return a[n - 1];
+}
+
+int
+main (void)
+{
+  int a[6] = { };
+  return foo (3, a);
+}
--- gcc/testsuite/c-c++-common/ubsan/vla-2.c.mp	2013-11-01 18:54:08.840202633 +0100
+++ gcc/testsuite/c-c++-common/ubsan/vla-2.c	2013-11-01 18:53:48.957130838 +0100
@@ -0,0 +1,15 @@
+/* { dg-do run } */
+/* { dg-options "-fsanitize=vla-bound -w" } */
+
+int
+main (void)
+{
+  const int t = 0;
+  struct s {
+    int x;
+    /* Don't instrument this one.  */
+    int g[t];
+  };
+
+  return 0;
+}
--- gcc/testsuite/c-c++-common/ubsan/vla-4.c.mp	2013-11-01 18:54:10.576209008 +0100
+++ gcc/testsuite/c-c++-common/ubsan/vla-4.c	2013-11-01 18:53:48.957130838 +0100
@@ -0,0 +1,13 @@
+/* { dg-do run } */
+/* { dg-options "-fsanitize=vla-bound" } */
+
+int
+main (void)
+{
+  int x = 1;
+  /* Check that the size of an array is evaluated only once.  */
+  int a[++x];
+  if (x != 2)
+    __builtin_abort ();
+  return 0;
+}
--- gcc/testsuite/c-c++-common/ubsan/vla-1.c.mp	2013-11-01 18:54:07.233196627 +0100
+++ gcc/testsuite/c-c++-common/ubsan/vla-1.c	2013-11-01 18:53:48.958130842 +0100
@@ -0,0 +1,48 @@
+/* { dg-do run } */
+/* { dg-options "-fsanitize=vla-bound -w" } */
+
+static int
+bar (void)
+{
+  return -42;
+}
+
+typedef long int V;
+int
+main (void)
+{
+  int x = -1;
+  double di = -3.2;
+  V v = -666;
+
+  int a[x];
+  int aa[x][x];
+  int aaa[x][x][x];
+  int b[x - 4];
+  int c[(int) di];
+  int d[1 + x];
+  int e[1 ? x : -1];
+  int f[++x];
+  int g[(signed char) --x];
+  int h[(++x, --x, x)];
+  int i[v];
+  int j[bar ()];
+
+  return 0;
+}
+
+/* { dg-output "variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -5(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -3(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value 0(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value 0(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -1(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -666(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*variable length array bound evaluates to non-positive value -42(\n|\r\n|\r)" } */
--- gcc/asan.c.mp	2013-11-01 18:53:17.445015000 +0100
+++ gcc/asan.c	2013-11-01 18:53:48.959130846 +0100
@@ -2021,6 +2021,9 @@ initialize_sanitizer_builtins (void)
   tree BT_FN_VOID = build_function_type_list (void_type_node, NULL_TREE);
   tree BT_FN_VOID_PTR
     = build_function_type_list (void_type_node, ptr_type_node, NULL_TREE);
+  tree BT_FN_VOID_PTR_PTR
+    = build_function_type_list (void_type_node, ptr_type_node,
+				ptr_type_node, NULL_TREE);
   tree BT_FN_VOID_PTR_PTR_PTR
     = build_function_type_list (void_type_node, ptr_type_node,
 				ptr_type_node, ptr_type_node, NULL_TREE);

	Marek