usercopy: WARN() on slab cache usercopy region violations

usercopy: WARN() on slab cache usercopy region violations

This patch adds checking of usercopy cache whitelisting, and is modified
from Brad Spengler/PaX Team's PAX_USERCOPY whitelisting code in the
last public patch of grsecurity/PaX based on my understanding of the
code. Changes or omissions from the original code are mine and don't
reflect the original grsecurity/PaX code.

The SLAB and SLUB allocators are modified to WARN() on all copy operations
in which the kernel heap memory being modified falls outside of the cache's
defined usercopy region.

Based on an earlier patch from David Windsor.

Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Laura Abbott <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>