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ubsan: Avoid narrowing of multiply for -fsanitize=signed-integer-overflow [PR108256]

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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.

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.
This commit is contained in:
Jakub Jelinek 2023-01-04 10:52:49 +01:00
parent 44baa34157
commit 8692b15ae7
3 changed files with 38 additions and 1 deletions
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8
gcc/convert.cc
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@ -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. */

4
gcc/fold-const.cc
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@ -9574,7 +9574,9 @@ fold_unary_loc (location_t loc, enum tree_code code, tree type, tree op0)
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;

27
gcc/testsuite/c-c++-common/ubsan/pr108256.c Normal file
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@ -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'" } */