Capability Domain Management via Program Counter State Transition

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Solution Overview

Problem

In capability-based architectures, there is a need for an efficient and reliable mechanism to alter the capability domain of processing circuitry, which requires access to memory addresses not accessible within the current capability domain, posing challenges in modifying the constraints and permissions.

Innovation Solution

The introduction of a program counter capability storage element that allows the processing circuitry to transition between a default and an executive state, enabling modification of the capability domain by relaxing constraints, allowing access to additional memory addresses and regions through mechanisms like branch instructions and banked capability storage elements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the processing circuitry operates in a capability domain with constrained capabilities, then security and reliability are improved, but the ability to modify the capability domain is worsened

Engineering Contradiction:

Improvecapability domain securityVSAvoidcapability domain modifiability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The system dynamically switches between two operational states: a default state where the program counter capability enforces capability domain constraints for security, and an executive state where constraints are relaxed to allow modification of the capability domain. This dynamic state transition resolves the contradiction by making the system's security and modifiability characteristics adaptable rather than fixed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The capability state parameter stored in the program counter capability storage element is used to control the degree of constraint enforcement. When this parameter indicates the executive state, the system allows access to memory addresses outside the current capability domain, enabling modification. When it indicates the default state, normal constraint enforcement resumes, maintaining security.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the processing circuitry accesses memory addresses outside the current capability domain, then the ability to modify the capability domain is improved, but security constraints are worsened

Engineering Contradiction:

Improvecapability domain modifiabilityVSAvoidunauthorized memory access

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

Before allowing access to memory addresses outside the current capability domain, the system preliminarily checks the capability state parameter stored in the program counter capability storage element. Only when this parameter indicates the executive state does the system permit such access, thereby preventing unauthorized memory access while still allowing legitimate capability domain modifications.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The program counter capability storage element acts as an intermediary mechanism that mediates between security constraints and modifiability requirements. It stores the capability state parameter that determines whether the processing circuitry should enforce capability domain constraints or allow relaxed access for modification purposes.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If the processing circuitry operates in a less constrained manner, then the ability to modify capabilities is improved, but the precision of capability constraints is worsened

Engineering Contradiction:

Improvecapability modification abilityVSAvoidcapability constraint precision

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The system dynamically adjusts the precision of capability constraints based on the operational state. In the default state, capability constraints are enforced with high precision to maintain security. In the executive state, the system temporarily reduces constraint precision to allow capability domain modification, then restores precision after the transition.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS11347508B2Apparatus and method for managing a capability domain

Publication Date: 2022.05.31 ARM LTD

AI summary

An apparatus and method are provided for managing a capability domain. The apparatus has processing circuitry for executing instructions, the processing circuitry when in a default state being arranged to operate in a capability domain comprising capabilities used to constrain operations performed by the processing circuitry when executing the instructions. A program counter capability storage element is also provided to store a program counter capability used by the processing circuitry to determine a program counter value. The program counter capability is arranged to identify a capability state for the processing circuitry. The processing circuitry is then arranged, when the capability state indicates the default state, to operate in the capability domain. However, when the capability state indicates the executive state, the processing circuitry is arranged to operate in a manner less constrained than when in the default state so as to allow modification of the capability domain. This provides a simple and effective mechanism for selectively allowing the apparatus to modify the capability domain.