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Privilege rings for the x86 available in protected mode. In computer science, hierarchical protection domains, [1] [2] often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance) and malicious behavior (by providing computer security).
Example of privilege ring usage in an operating system using all rings. In protected mode, there are four privilege levels or rings, numbered from 0 to 3, with ring 0 being the most privileged and 3 being the least. The use of rings allows for system software to restrict tasks from accessing data, call gates or executing privileged instructions ...
System Management Mode (SMM, sometimes called ring −2 in reference to protection rings) [1] [2] is an operating mode of x86 central processor units (CPUs) in which all normal execution, including the operating system, is suspended.
The ME is colloquially categorized as ring −3, below System Management Mode (ring −2) and the hypervisor (ring −1), all running at a higher privilege level than the kernel (ring 0). The Intel Management Engine (ME), also known as the Intel Manageability Engine, [1] [2] is an autonomous subsystem that has been incorporated in virtually all ...
These instructions permit entering and exiting a virtual execution mode where the guest OS perceives itself as running with full privilege (ring 0), but the host OS remains protected. As of 2015, almost all newer server, desktop and mobile Intel processors support VT-x, with some of the Intel Atom processors as the primary exception. [24]
Multics was the first user of call gates. The Honeywell 6180 had call gates as part of the architecture, but Multics simulated them on the older GE 645.. OS/2 was an early user of Intel call gates to transfer between application code running in ring 3, privileged code running in ring 2, and kernel code in ring 0.
The Global Descriptor Table (GDT) is a data structure used by Intel x86-family processors starting with the 80286 in order to define the characteristics of the various memory areas used during program execution, including the base address, the size, and access privileges like executability and writability.
Multics hardware was the first significant implementation of ring security, but many other hardware platforms have been designed along similar lines, including the Intel 80286 protected mode, and the IA-64 as well, though it is referred to by a different name in these cases. Mode protection may extend to resources beyond the CPU hardware itself.