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

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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.
This commit is contained in:
Jakub Jelinek 2024-02-06 13:00:04 +01:00
parent 483c061d69
commit d3eac7d96d
2 changed files with 19 additions and 0 deletions
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5
gcc/gimple-fold.cc
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@ -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. */

14
gcc/testsuite/gcc.dg/asan/pr110676.c Normal file
View file

@ -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.*" } */