Capability Permission Interpretation via Flag Logic
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Solution Overview
Problem
In capability-based architectures, the number of permissions associated with a capability is often constrained by the limited size of capability storage elements, making it difficult to extend permissions without increasing the number of permission flags, which limits flexibility and security.
Innovation Solution
The processing circuitry analyzes capability storage elements using an alternative interpretation of permission flags to derive an enlarged set of permissions, including additional permissions beyond the default set, without adding new flags, allowing for enhanced flexibility and security features like modifiable permissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of permission flags in a capability is increased to provide more permissions, then the flexibility and security of the capability-based architecture is improved, but the size of the capability storage element increases
Solution Approach 1:
The patent combines multiple permission flags into a single permission field that can represent multiple permission states. Instead of having separate flags for each permission (read, write, execute, etc.), the invention uses a unified permission field that encodes multiple permission attributes, thereby reducing the overall capability size while maintaining the ability to express multiple permissions.
Solution Approach 2:
The permission field is designed to serve multiple functions simultaneously. A single permission field can represent different permission types (read, write, execute, modify) and can be interpreted in different contexts. This multi-functional approach allows the capability to enforce multiple permission checks without requiring separate flags for each permission type.
2Adaptability or versatility
If additional permission flags are added to a capability to extend permissions, then the security and flexibility are enhanced, but the device complexity increases
Solution Approach 1:
The invention changes the parameter representation from multiple discrete boolean flags to a single multi-state permission field. This parameter transformation reduces the number of individual permission indicators while maintaining the ability to represent complex permission states through different encodings within the unified field.
3Productivity
If the capability storage element size is reduced to maintain fixed register sizes, then the efficiency of capability processing is improved, but the number of permissions that can be enforced is reduced
Solution Approach 1:
By merging multiple permission flags into a single permission field, the invention reduces the overall capability size, allowing fixed-size registers to accommodate more capability information. This consolidation maintains processing efficiency while preserving the ability to enforce multiple permissions through the unified field's multiple states.
Data Source
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AI summary
An apparatus and method are provided for interpreting permissions associated with a capability. The apparatus has processing circuitry for executing instructions in order to perform operations, and a capability storage element accessible to the processing circuitry and arranged to store a capability used to constrain at least one operation performed by the processing circuitry when executing the instructions. The capability identifies a plurality N of default permissions whose state, in accordance with a default interpretation, is determined from N permission flags provided in the capability. In accordance with the default interpretation, each permission flag is associated with one of the default permissions. The processing circuitry is then arranged to analyse the capability in accordance with an alternative interpretation, in order to derive, from logical combinations of the N permission flags, state for an enlarged set of permissions, where the enlarged set comprises at least N+1 permissions. This provides a mechanism for encoding additional permissions into capabilities without increasing the number of permission flags required, whilst still retaining desirable behaviour.