UPSTREAM: mm: SLUB hardened usercopy support

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: Kees Cook <keescook@chromium.org>
Tested-by: Michael Ellerman <mpe@ellerman.id.au>
Reviwed-by: Laura Abbott <labbott@redhat.com>

Change-Id: I52dc6fb3a3492b937d52b5cf9c046bf03dc40a3a
(cherry picked from commit ed18adc1)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>