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: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: kasan-dev@xxxxxxxxxxxxxxxx Cc: linux-mm@xxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- mm/kasan/generic.c | 2 +- mm/kasan/sw_tags.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c index df6627f62402..f9bc29ae09bd 100644 --- a/mm/kasan/generic.c +++ b/mm/kasan/generic.c @@ -171,7 +171,7 @@ static __always_inline bool check_region_inline(const void *addr, if (unlikely(size == 0)) return true; - if (unlikely(addr + size < addr)) + if (unlikely(add_would_overflow(addr, size))) return !kasan_report(addr, size, write, ret_ip); if (unlikely(!addr_has_metadata(addr))) diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c index 220b5d4c6876..79a3bbd66c32 100644 --- a/mm/kasan/sw_tags.c +++ b/mm/kasan/sw_tags.c @@ -80,7 +80,7 @@ bool kasan_check_range(const void *addr, size_t size, bool write, if (unlikely(size == 0)) return true; - if (unlikely(addr + size < addr)) + if (unlikely(add_would_overflow(addr, size))) return !kasan_report(addr, size, write, ret_ip); tag = get_tag((const void *)addr); -- 2.34.1
