How is a Crash implemented? Mach and POSIX Signals

The KERN_INVALID_ADDRESS return code indicates an unsafe memory access; outside the virtual address space of the process. This is a classic attack vector for Level 9 system compromise, so crashing really is the best outcome here. 

The virtual memory subsystem vm ultimately invokes the exception handling subsystem, which transforms the kernel exception into a higher-level exception that terminates the process.

These systems are all part of