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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).
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 ...
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 ...
Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts.
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.
When Intel introduced the Intel 80386 processor, in addition to expanding the iRMX RTOS to support 32-bit registers, iRMX III also included support for the four distinct protection rings (named rings 0 through 3) which describe the protected-mode mechanism of the Intel 32-bit architecture. In practice very few systems have ever used more than ...
The principle of least privilege demonstrated by privilege rings for the Intel x86. If execution picks up after the crash by loading and running trojan code, the author of the trojan code can usurp control of all processes. The principle of least privilege forces code to run with the lowest privilege/permission level possible.