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 Notable, 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, unsigned, or pointer types. Refactor open-coded unsigned 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/27 [2] Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: kvm@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- virt/kvm/coalesced_mmio.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c index 1b90acb6e3fe..0a3b706fbf4c 100644 --- a/virt/kvm/coalesced_mmio.c +++ b/virt/kvm/coalesced_mmio.c @@ -25,17 +25,19 @@ static inline struct kvm_coalesced_mmio_dev *to_mmio(struct kvm_io_device *dev) static int coalesced_mmio_in_range(struct kvm_coalesced_mmio_dev *dev, gpa_t addr, int len) { + gpa_t sum; + /* is it in a batchable area ? * (addr,len) is fully included in * (zone->addr, zone->size) */ if (len < 0) return 0; - if (addr + len < addr) + if (check_add_overflow(addr, len, &sum)) return 0; if (addr < dev->zone.addr) return 0; - if (addr + len > dev->zone.addr + dev->zone.size) + if (sum > dev->zone.addr + dev->zone.size) return 0; return 1; } -- 2.34.1
