In an effort to separate intentional arithmetic wrap-around from unexpected wrap-around, we need to refactor places that depend on this kind of math. One of the most common code patterns of this is: VAR + value < VAR Notably, this is considered "undefined behavior" for signed and pointer types, which the kernel works around by using the -fno-strict-overflow option in the build[1] (which used to just be -fwrapv). Regardless, we want to get the kernel source to the position where we can meaningfully instrument arithmetic wrap-around conditions and catch them when they are unexpected, regardless of whether they are signed[2], unsigned[3], or pointer[4] types. Refactor open-coded wrap-around addition test to use add_would_overflow(). This paves the way to enabling the wrap-around sanitizers in the future. Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] Link: https://github.com/KSPP/linux/issues/26 [2] Link: https://github.com/KSPP/linux/issues/27 [3] Link: https://github.com/KSPP/linux/issues/344 [4] Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx> Cc: Janosch Frank <frankja@xxxxxxxxxxxxx> Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx> Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> Cc: Heiko Carstens <hca@xxxxxxxxxxxxx> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> Cc: Sven Schnelle <svens@xxxxxxxxxxxxx> Cc: kvm@xxxxxxxxxxxxxxx Cc: linux-s390@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- arch/s390/mm/gmap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c index 6f96b5a71c63..977b61ab59f2 100644 --- a/arch/s390/mm/gmap.c +++ b/arch/s390/mm/gmap.c @@ -411,7 +411,7 @@ int gmap_unmap_segment(struct gmap *gmap, unsigned long to, unsigned long len) BUG_ON(gmap_is_shadow(gmap)); if ((to | len) & (PMD_SIZE - 1)) return -EINVAL; - if (len == 0 || to + len < to) + if (len == 0 || add_would_overflow(to, len)) return -EINVAL; flush = 0; @@ -443,7 +443,7 @@ int gmap_map_segment(struct gmap *gmap, unsigned long from, BUG_ON(gmap_is_shadow(gmap)); if ((from | to | len) & (PMD_SIZE - 1)) return -EINVAL; - if (len == 0 || from + len < from || to + len < to || + if (len == 0 || add_would_overflow(from, len) || add_would_overflow(to, len) || from + len - 1 > TASK_SIZE_MAX || to + len - 1 > gmap->asce_end) return -EINVAL; -- 2.34.1
