Memory Access Control Circuit for Trusted Execution Environment Security
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Solution Overview
Problem
Current security measures in devices are inadequate for protecting sensitive information, as they often rely on software solutions that are weaker than hardware solutions, leaving vulnerabilities that attackers can exploit, even with root privileges.
Innovation Solution
An apparatus and method for controlling access to a data memory that utilizes a control circuit to determine if a memory area should be accessed exclusively from a Trusted Execution Environment (TEE), and if so, enforces access based on security information indicating the processor's secure mode, thereby preventing unauthorized access, even from attackers with root privileges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If software security controls are used to protect sensitive information, then device complexity is reduced and ease of operation is improved, but security reliability deteriorates allowing attackers to compromise the system
Solution Approach 1:
The patent segments the execution environment into two distinct modes: a trusted execution environment (secure mode) and a non-trusted execution environment (non-secure mode). This segmentation is enforced through hardware-level mode bits that partition the processor's operational states, ensuring that sensitive operations occur exclusively in the secure mode while non-sensitive operations can run in non-secure mode. The memory access control is also segmented to differentiate between secure and non-secure access paths.
Solution Approach 2:
The patent introduces a trusted execution environment as an intermediary layer between the attacker (even with root privileges) and the sensitive information. This intermediary enforces security policies by checking mode bits and controlling memory access based on the current execution mode, thereby protecting critical assets without requiring complete hardware mitigation across all system components.
2Reliability
If hardware security mitigation is implemented for all use cases, then security reliability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies security controls locally rather than universally. Specifically, it implements hardware-level security mechanisms (mode bits, trusted execution environment) only for specific memory areas and execution contexts that require protection, while allowing other system components to operate without equivalent hardware security infrastructure. This selective application of security reduces overall device complexity while maintaining protection for critical assets.
Solution Approach 2:
The patent changes the operational parameters of the processor by introducing mode bits that alter the execution context. These parameter changes enable the system to dynamically switch between secure and non-secure modes, allowing hardware security to be activated only when needed for specific operations or memory accesses, rather than requiring constant hardware-level protection for all system operations.
3Reliability
If exclusive access control for TEE is enforced at hardware level, then security reliability is improved blocking root privilege attacks, but ease of operation and system flexibility deteriorate
Solution Approach 1:
The patent implements dynamic access control where the security constraints are not static but change based on the current execution mode. The mode bits can be set or cleared to dynamically switch between trusted and non-trusted execution environments, allowing the system to adapt security restrictions in real-time based on operational requirements. This dynamic approach maintains security while preserving operational flexibility.
Solution Approach 2:
The trusted execution environment mechanism serves multiple functions: it provides security isolation, controls memory access, manages execution modes, and protects against various attack vectors including root privilege exploitation. By making this single hardware mechanism multi-functional, the patent reduces the need for separate control mechanisms, thereby maintaining ease of operation while achieving comprehensive security protection.
Data Source
AI summary
An apparatus for controlling access to a data memory is provided. The apparatus includes an input interface configured to receive a request from an external processor circuit for accessing a memory area of the data memory. The apparatus additionally includes a control circuit configured to determine whether the memory area is to be accessed exclusively from within a trusted execution environment. Further, if it is determined that the memory area is to be accessed exclusively from within the trusted execution environment, the control circuit is configured to control access to the memory area of the data memory based on security information indicating whether the external processor circuit is operating in a secure mode related to the trusted execution environment.