[gcc r14-8825] asan: Don't fold some strlens with -fsanitize=address [PR110676]

[gcc r14-8825] asan: Don't fold some strlens with -fsanitize=address [PR110676]

[Jakub Jelinek]

https://gcc.gnu.org/g:d3eac7d96de790df51859f63c13838f153b416de

commit r14-8825-gd3eac7d96de790df51859f63c13838f153b416de
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Feb 6 13:00:04 2024 +0100

    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:
---
 gcc/gimple-fold.cc                   |  5 +++++
 gcc/testsuite/gcc.dg/asan/pr110676.c | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index a46e640692d3..5191102df688 100644
--- 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
index 000000000000..0ae6fdd67b59
--- /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.*" } */