Interrupt Controller TEE Execution Isolation
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Solution Overview
Problem
Existing hardware-based mechanisms for providing a trusted execution environment are complex and costly, making them prohibitive for implementations that do not have hardware mechanisms for separating secure and normal worlds within an apparatus.
Innovation Solution
An apparatus with processing circuitry and interrupt controller circuitry that selects and executes a trusted execution environment (TEE) interrupt service routine, inhibiting further interrupts until completion, and includes code and data protection mechanisms to prevent unauthorized modification and access, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware-based mechanisms with separate secure and normal worlds are used, then security strength is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the essential security functions from complex hardware-based secure world mechanisms and implements them through a simplified software-based TEE interrupt service routine. The TEE interrupt request mechanism isolates the critical security functionality (handling trusted interrupts) from the normal interrupt processing, providing security without requiring full hardware-based secure world separation.
Solution Approach 2:
The patent creates a software-based copy of the secure world functionality through the TEE interrupt service routine. Instead of requiring physical hardware separation, the TEE ISR acts as a software replica that provides the same security guarantees for trusted execution, thereby reducing hardware complexity while maintaining security strength.
2Reliability
If hardware-based secure world separation is implemented, then trusted execution is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive hardware-based secure world mechanisms with a software-based TEE interrupt service routine that can be implemented on standard processors. This software-based approach is more economical to manufacture and deploy, providing trusted execution capabilities without the high cost of specialized hardware security modules or secure world processors.
3Productivity
If interruptibility is allowed during TEE execution, then system responsiveness is improved, but security is compromised
Solution Approach 1:
The patent segments the interrupt handling system into two distinct paths: trusted TEE interrupts that invoke the TEE interrupt service routine (which cannot be interrupted), and normal interrupts that follow the standard interrupt handling path. This segmentation ensures that security-critical TEE execution remains non-interruptible while maintaining system responsiveness through normal interrupt handling for non-critical operations.
4Reliability
If code protection mechanisms are added, then authenticity is improved, but device complexity increases
Solution Approach 1:
The patent implements code protection through self-service mechanisms where the TEE interrupt service routine includes built-in authentication and verification capabilities. The system automatically verifies the authenticity of the TEE ISR code through cryptographic signatures or hash verification, eliminating the need for external complex verification hardware and providing authenticity guarantees through self-contained protection mechanisms.
Data Source
AI summary
An apparatus and method are described for providing a trusted execution environment. The apparatus comprises processing circuitry to execute program code, and interrupt controller circuitry, responsive to receipt of one or more interrupt requests, to select a given interrupt request from amongst the one or more interrupt requests, and to issue an interrupt signal to the processing circuitry identifying a given interrupt service routine providing program code to be executed by the processing circuitry to service the given interrupt request. The interrupt controller circuitry is responsive to the given interrupt request being a trusted execution environment (TEE) interrupt request, to issue the interrupt signal to identify as the given interrupt service routine a TEE interrupt service routine, and to inhibit issuance of any further interrupt signal until the TEE interrupt service routine has been executed by the processing circuitry. The interrupt controller circuitry comprises code protection circuitry to inhibit unauthorised modification of the TEE interrupt service routine, and data protection circuitry to inhibit unauthorised access to confidential data processed by the TEE interrupt service routine.