asan: Don't fold some strlens with -fsanitize=address [PR110676]

The UB on the following testcase isn't diagnosed by -fsanitize=address,
because we see that the array has a single element and optimize the
strlen to 0.  I think it is fine to assume e.g. for range purposes the
lower bound for the strlen as long as we don't try to optimize
strlen (str)
where we know that it returns [26, 42] to
26 + strlen (str + 26), but for the upper bound we really want to punt
on optimizing that for -fsanitize=address to read all the bytes of the
string and diagnose if we run to object end etc.

2024-02-06  Jakub Jelinek  <jakub@redhat.com>

	PR sanitizer/110676
	* gimple-fold.cc (gimple_fold_builtin_strlen): For -fsanitize=address
	reset maxlen to sizetype maximum.

	* gcc.dg/asan/pr110676.c: New test.

diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index a46e640692d3bcc4ae9265e282f304b85850d4c9..5191102df6882ba552db856ec62457ce9ae0f563 100644 (file)
--- a/gcc/gimple-fold.cc
+++ b/gcc/gimple-fold.cc
@@ -4019,6 +4019,11 @@ gimple_fold_builtin_strlen (gimple_stmt_iterator *gsi)
       maxlen = wi::to_wide (max_object_size (), prec) - 2;
     }
 
+  /* For -fsanitize=address, don't optimize the upper bound of the
+     length to be able to diagnose UB on non-zero terminated arrays.  */
+  if (sanitize_flags_p (SANITIZE_ADDRESS))
+    maxlen = wi::max_value (TYPE_PRECISION (sizetype), UNSIGNED);
+
   if (minlen == maxlen)
     {
       /* Fold the strlen call to a constant.  */

diff --git a/gcc/testsuite/gcc.dg/asan/pr110676.c b/gcc/testsuite/gcc.dg/asan/pr110676.c
new file mode 100644 (file)
index 0000000..0ae6fdd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/asan/pr110676.c
@@ -0,0 +1,14 @@
+/* PR sanitizer/110676 */
+/* { dg-do run } */
+/* { dg-skip-if "" { *-*-* } { "*" } { "-O0" } } */
+/* { dg-shouldfail "asan" } */
+
+int
+main ()
+{
+  char s[1] = "A";
+  return __builtin_strlen (s);
+}
+
+/* { dg-output "ERROR: AddressSanitizer: stack-buffer-overflow on address.*(\n|\r\n|\r)" } */
+/* { dg-output "READ of size.*" } */