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 pointer wrap-around addition test to use check_add_overflow(), retaining the result for later usage (which removes the redundant open-coded addition). This paves the way to enabling the unsigned wrap-around sanitizer[2] 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: Vineet Gupta <vgu...@kernel.org> Cc: Luis Chamberlain <mcg...@kernel.org> Cc: Song Liu <s...@kernel.org> Cc: Yihao Han <hanyi...@vivo.com> Cc: Thomas Gleixner <t...@linutronix.de> Cc: "dean.yang_cp" <yangdianq...@yulong.com> Cc: Jinchao Wang <w...@cdjrlc.com> Cc: linux-snps-...@lists.infradead.org Signed-off-by: Kees Cook <keesc...@chromium.org> --- arch/arc/kernel/unwind.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/arc/kernel/unwind.c b/arch/arc/kernel/unwind.c index 9270d0a713c3..8924fa2a8f29 100644 --- a/arch/arc/kernel/unwind.c +++ b/arch/arc/kernel/unwind.c @@ -612,6 +612,7 @@ static signed fde_pointer_type(const u32 *cie) const char *aug; const u8 *end = (const u8 *)(cie + 1) + *cie; uleb128_t len; + const u8 *sum; /* check if augmentation size is first (and thus present) */ if (*ptr != 'z') @@ -630,10 +631,10 @@ static signed fde_pointer_type(const u32 *cie) version <= 1 ? (void) ++ptr : (void)get_uleb128(&ptr, end); len = get_uleb128(&ptr, end); /* augmentation length */ - if (ptr + len < ptr || ptr + len > end) + if (check_add_overflow(ptr, len, &sum) || sum > end) return -1; - end = ptr + len; + end = sum; while (*++aug) { if (ptr >= end) return -1; -- 2.34.1