US 5,634,036 AGranted

Method and apparatus for protecting memory with variable visibility of segment descriptor tables

AssigneeIntel Corporation

InventorClifton W. Laney

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Abstract

An additional function is provided to an otherwise conventional operating system for superimposing visibility windows on the GDT and the LDTs for the purpose of memory protection. In a first embodiment, the operating system is also provided with a first additional control logic for selectively invoking the visibility window function to impose visibility windows of different window sizes for different tasks. In a second embodiment, the operating system is provided with a second additional control logic for selectively invoking the visibility window function to impose visibility windows of different window sizes for different operating system functions. In a third embodiment, the operating system is provided with the first as well as the second additional control logic.

Claims13

Dependent claims

A computer system comprising:

a) random-access-memory (RAM) for storing loaded program modules and associated data, including an operating system load module and a segment descriptor table,
the segment descriptor table when created having a first and a second plurality of segment descriptors describing memory segments of a first and a second memory type of the computer system,
the operating system having memory management functions that include a visibility window function for dynamically superimposing a first and a second visibility window over the content of the segment descriptor table, exposing the first plurality of segment descriptors for tasks being executed with a first memory configuration, and the first as well as at least a portion Of the second plurality of segment descriptors for tasks being executed with a second memory configuration, during operation;
b) a processor coupled to the memory for executing tasks;
and
c) non-volatile storage coupled to the processor and memory storing program objects from which the loaded program modules are created, including the operating system.

3 more elements

A method for protecting memory of a computer system, the method comprising the steps of:

a) while a task is being switched into context, determining whether the task is to be executed with a non-default memory configuration, such that a non-default visibility window is to be superimposed on a segment descriptor table to expose at least a portion of a second as well as a first plurality of segment descriptors describing memory segments of a second as well as a first memory type of the computer system, the second plurality of segment descriptors being normally hidden if a default visibility window is employed;
and
b) upon determining that the non-default visibility window is to be superimposed, invoking a visibility window function to superimpose the non-default visibility window over the segment descriptor table accordingly.

Dependencies are inferred from the claim text.