I doubt that N. Korea can produce an inertial guidance system that could guide a rocket to Hawaii or Guam. But it would be easy for them to use a commercially available GPS system to accomplish the same thing.
A basic part of our strategic defense should be to shut off the GPS satellites in that part of the world when it is detected that N. Korea has launched missiles. I don't know if that is the plan or how to reach the right person who would make that decision. Hopefully someone who reads this can make the suggestion.