ntoskrnl easily crashable from usermode

Our ntoskrnl lacks checks of buffer checks for reading and writing data to
buffer (e.g. using MmCopyFromCaller() and MmCopyToCaller()) passed to functions
in lots of functions. That means if you pass an invalid pointer from usermode to
a ntoskrnl function, you can easily crash the entire system. This needs to be
fixed soon because it's a major system violability.