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. 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. 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). This is generally hardware-enforced by some CPU architectures that provide different CPU modes at the hardware or microcode level. A protection ring is one of two or more hierarchical levels or layers of privilege within the architecture of a computer system. This approach is diametrically opposite to that of capability-based security.Ĭomputer operating systems provide different levels of access to resources. 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). Privilege rings for the x86 available in protected mode
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