3 - Operating Systems

Question 1

TCB requirements

Answer 1

Tamper-proof - hardware support for memory protection, processor execution modes (sys/user), privileged instructions, system calls

Complete mediation - No protected resource can be accessed without going through TCB

Correct - small and simple, correct, secure coding

Question 2

System calls

Answer 2

Transfers control between user and system code

Calls go through call gates and return to user code

Execution mode/privilege ring changes

Question 3

OS isolation from application code

Answer 3

Kernel resides in each processes address space

Process can only cross the fence in limited ways

Question 4

Address translation

Answer 4

OS maps logical virtual addresses on to physical memory frames

Question 5

Isolating users

Answer 5

OS uses hardware support for memory protection