[PATCH] x86_64: Check for bad elf entry address.

Fixes a local DOS on Intel systems that lead to an endless
recursive fault.  AMD machines don't seem to be affected.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>