In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults (fault tolerance) and malicious behaviour (computer security). This approach is diametrically opposite to that of capability-based security.
Computer operating systems provide different levels of access to resources. A protection ring is one of two or more hierarchical levels or layers of privilege within the architecture of a computer system. This is generally hardware-enforced by some CPU architectures that provide different CPU modes at the hardware or microcode level.
Rings are arranged in a hierarchy from most privileged (most trusted, usually numbered zero) to least privileged (least trusted, usually with the highest ring number). On most operating systems, Ring 0 is the level with the most privileges and interacts most directly with the physical hardware such as the CPU and memory.
Special gates between rings are provided to allow an outer ring to access an inner ring’s resources in a predefined manner, as opposed to allowing arbitrary usage. Correctly gating access between rings can improve security by preventing programs from one ring or privilege level from misusing resources intended for programs in another. For example, spyware running as a user program in Ring 3 should be prevented from turning on a web camera without informing the user, since hardware access should be a Ring 1 function reserved for device drivers. Programs such as web browsers running in higher numbered rings must request access to the network, a resource restricted to a lower numbered ring.
“They provide strict boundaries and definitions on what the processes that work within each ring can access” is incorrect. This is in fact one of the characteristics of a ring protection system.
“Programs operating in inner rings are usually referred to as existing in a privileged mode” is incorrect. This is in fact one of the characteristics of a ring protection system.
“They support the CIA triad requirements of multitasking operating systems” is incorrect. This is in fact one of the characteristics of a ring protection system.
Reference(s) used for this question:
CBK, pp. 310-311 AIO3, pp. 253-256 AIOv4 Security Architecture and Design (pages 308 -310) AIOv5 Security Architecture and Design (pages 309 -312)