Page 643 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Essential Security Protection Mechanisms

The need for security mechanisms within an operating system comes
down to one simple fact: software should not be trusted. Third-party
software is inherently untrustworthy, no matter who or where it comes

from. This is not to say that all software is evil. Instead, this is a
protection stance—because all third-party software is written by
someone other than the OS creator, that software might cause
problems. Thus, treating all non-OS software as potentially damaging
allows the OS to prevent many disastrous occurrences through the use

of software management protection mechanisms. The OS must employ
protection mechanisms to keep the computing environment stable and
to keep processes isolated from each other. Without these efforts, the
security of data could never be reliable or even possible.

Computer system designers should adhere to a number of common
protection mechanisms when designing secure systems. These
principles are specific instances of the more general security rules that

govern safe computing practices. Designing security into a system
during the earliest stages of development will help ensure that the
overall security architecture has the best chance for success and
reliability. In the following sections, we’ll divide the discussion into
two areas: technical mechanisms and policy mechanisms.

Technical Mechanisms

Technical mechanisms are the controls that system designers can
build right into their systems. We’ll look at five: layering, abstraction,
data hiding, process isolation, and hardware segmentation.

Layering

By layering processes, you implement a structure similar to the ring
model used for operating modes (and discussed earlier in this chapter)

and apply it to each operating system process. It puts the most
sensitive functions of a process at the core, surrounded by a series of
increasingly larger concentric circles with correspondingly lower
sensitivity levels (using a slightly different approach, this is also