A flaw in the protection system of many operating systems is argument passing. Often, a common shared stack is used by all nested routines for arguments as well as for the remainder of the context of each calling process.

Question

Explain what vulnerabilities this flaw presents.

Explain how the flaw can be controlled. The shared stack is still to be used for passing arguments and storing context.

Answer 1

One difficulty is that any routine can be faulty: routine A puts an incorrect value on the stack and B retrieves it, not knowing it is faulty. Routine B can be self-­?defensive, checking the reasonableness of the value. Obviously, without duplicating the work of A, B cannot determine whether the value isexactly right.

A second difficulty is stack depth:any routine can use the entire stack.

A third difficulty is that any routine can modify results of any other routine:routine A puts a value on the stack, and routine B subsequently changes that value toanything.