From: Jakub Jelinek <jakub@redhat.com>
To: Richard Biener <rguenther@suse.de>
Cc: gcc-patches@gcc.gnu.org
Subject: [PATCH] ubsan: Avoid narrowing of multiply for -fsanitize=signed-integer-overflow [PR108256]
Date: Wed, 4 Jan 2023 10:08:53 +0100 [thread overview]
Message-ID: <Y7VCJRmHC/U+F53U@tucnak> (raw)
Hi!
We shouldn't narrow multiplications originally done in signed types,
because the original multiplication might overflow but the narrowed
one will be done in unsigned arithmetics and will never overflow.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2023-01-04 Jakub Jelinek <jakub@redhat.com>
PR sanitizer/108256
* convert.cc (do_narrow): Punt for MULT_EXPR if original
type doesn't wrap around and -fsanitize=signed-integer-overflow
is on.
* fold-const.cc (fold_unary_loc) <CASE_CONVERT>: Likewise.
* c-c++-common/ubsan/pr108256.c: New test.
--- gcc/convert.cc.jj 2023-01-02 09:32:25.123245723 +0100
+++ gcc/convert.cc 2023-01-03 10:02:36.309706050 +0100
@@ -384,6 +384,14 @@ do_narrow (location_t loc,
&& sanitize_flags_p (SANITIZE_SI_OVERFLOW))
return NULL_TREE;
+ /* Similarly for multiplication, but in that case it can be
+ problematic even if typex is unsigned type - 0xffff * 0xffff
+ overflows in int. */
+ if (ex_form == MULT_EXPR
+ && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (expr))
+ && sanitize_flags_p (SANITIZE_SI_OVERFLOW))
+ return NULL_TREE;
+
/* But now perhaps TYPEX is as wide as INPREC.
In that case, do nothing special here.
(Otherwise would recurse infinitely in convert. */
--- gcc/fold-const.cc.jj 2023-01-02 09:32:32.756135438 +0100
+++ gcc/fold-const.cc 2023-01-03 10:30:05.492239455 +0100
@@ -9574,7 +9574,9 @@ fold_unary_loc (location_t loc, enum tre
if (INTEGRAL_TYPE_P (type)
&& TREE_CODE (op0) == MULT_EXPR
&& INTEGRAL_TYPE_P (TREE_TYPE (op0))
- && TYPE_PRECISION (type) < TYPE_PRECISION (TREE_TYPE (op0)))
+ && TYPE_PRECISION (type) < TYPE_PRECISION (TREE_TYPE (op0))
+ && (TYPE_OVERFLOW_WRAPS (TREE_TYPE (op0))
+ || !sanitize_flags_p (SANITIZE_SI_OVERFLOW)))
{
/* Be careful not to introduce new overflows. */
tree mult_type;
--- gcc/testsuite/c-c++-common/ubsan/pr108256.c.jj 2023-01-03 10:14:49.064284638 +0100
+++ gcc/testsuite/c-c++-common/ubsan/pr108256.c 2023-01-03 10:43:58.838326443 +0100
@@ -0,0 +1,27 @@
+/* PR sanitizer/108256 */
+/* { dg-do run { target { lp64 || ilp32 } } } */
+/* { dg-options "-fsanitize=signed-integer-overflow" } */
+
+unsigned short
+foo (unsigned short x, unsigned short y)
+{
+ return x * y;
+}
+
+unsigned short
+bar (unsigned short x, unsigned short y)
+{
+ int r = x * y;
+ return r;
+}
+
+int
+main ()
+{
+ volatile unsigned short a = foo (0xffff, 0xffff);
+ volatile unsigned short b = bar (0xfffe, 0xfffe);
+ return 0;
+}
+
+/* { dg-output "signed integer overflow: 65535 \\\* 65535 cannot be represented in type 'int'\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*signed integer overflow: 65534 \\\* 65534 cannot be represented in type 'int'" } */
Jakub
next reply other threads:[~2023-01-04 9:09 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-04 9:08 Jakub Jelinek [this message]
2023-01-04 9:19 ` Richard Biener
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