Strictly it's only needed for eax.
It actually does a little more than strictly needed -- the other registers
are already zero extended.
Also remove the now unnecessary and non functional compat task check
in ptrace.
This is CVE-2007-4573
Found by Wojciech Purczynski
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
176df2457e