[$] Strict memcpy() bounds checking for the kernel

The C programming language is famously prone to memory-safety problemsthat lead to buffer overflows and a seemingly endless stream of securityvulnerabilities. But, even in C, it is possible to improve thesituation in many cases. One of those is the memcpy() family offunctions, which are used to efficiently copy or overwrite blocks ofmemory; with a bit of help from the compiler, those functions can beprevented from writing past the end of thedestination object they are passed. Enforcing that condition in the kernelis harder than one might expect, though, as thismassive patch set from Kees Cook shows.