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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 ...
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.
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]
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 ...
Intel Software Guard Extensions (SGX) is a set of instruction codes implementing trusted execution environment that are built into some Intel central processing units (CPUs). They allow user-level and operating system code to define protected private regions of memory, called enclaves .
The FLAGS register is the status register that contains the current state of an x86 CPU.The size and meanings of the flag bits are architecture dependent. It usually reflects the result of arithmetic operations as well as information about restrictions placed on the CPU operation at the current time.