[$] Better handling of integer wraparound in the kernel

While the mathematical realm of numbers is infinite, computers are onlyable to represent a finite subset of them. That can lead to problems whenarithmetic operations would create numbers that the computer is unable tostore as the intended type. This condition, called "overflow" or"wraparound" depending on the context, can be the source of bugs, including unpleasant securityvulnerabilities, so it is worth avoiding. This patchseries from Kees Cook is intended to improve the kernel's handling ofthese situations, but it is running into a bit of resistance.