They should not be writable by any user.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Hao Wu <hao.wu@intel.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Alek Du <alek.du@intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>