Privilege Checking

General

The goal of privilege checking is to ensure that the currently executing program cannot access an area of memory unless permitted to do so. Any attempt to do so results in a General Protection (GP) exception.

Some Definitions

Before permitting access to a segment, the processor must verify that the currently executing program has sufficient privilege to access the segment. The three components involved in this comparison are:

  • The CPL (Current Privilege Level) of the currently executing program.

  • The RPL (Requestor Privilege Level) in the segment register.

  • The DPL (Descriptor Privilege Level) of the target code segment.

Definition of a Task

The term task is used many times throughout this book. In a multitasking OS, the ...

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