Solaris™ Internals: Core Kernel Components

2.1. Access to Kernel Services

The Solaris kernel insulates processes from kernel data structures and hardware by using two distinct processor execution modes: nonprivileged mode and privileged mode. Privileged mode is often referred to as kernel mode; nonprivileged mode is referred to as user mode.

In nonprivileged mode, a process can access only its own memory, whereas in privileged mode, access is available to all of the kernel's data structures and the underlying hardware. The kernel executes processes in nonprivileged mode to prevent user processes from accessing data structures or hardware registers that may affect other processes or the operating environment. Because only Solaris kernel instructions can execute in privileged mode, the ...