Privilege Levels

As discussed in an earlier chapter, the IA32 processors provide four privilege levels when executing in Protected Mode:

• Level zero is the highest privilege level. Typically, only the OS kernel will run with privilege level zero. This permits it to perform any operation.

• Level one is the next privilege level. It is typically assigned to high-priority device drivers and OS services. It could also be assigned to debuggers to protect them from alteration by low-priority device drivers and applications programs.

• Level two is typically assigned to lower-priority device drivers.

• Level three is the lowest priority and is typically assigned to applications programs. This prevents them from performing actions that would be injurious to the OS, debuggers, device drivers, or each other.