Under CONFIG_HARDENED_USERCOPY, this adds object size checking to the
SLUB allocator to catch any copies that may span objects. Includes a
redzone handling fix discovered by Michael Ellerman.

Based on code from PaX and grsecurity.
Signed-off-by: NKees Cook <keescook@chromium.org>
Tested-by: NMichael Ellerman <mpe@ellerman.id.au>
Reviwed-by: NLaura Abbott <labbott@redhat.com>