Non-Volatile Memory Access Control for Secure Boot Phases
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Solution Overview
Problem
Existing solutions are inefficient in preventing malicious codes and software from being introduced and executed during the boot sequence of electronic devices.
Innovation Solution
A non-volatile memory with an access control circuit that segregates codes into immutable and mutable zones, allowing execution of first-phase codes while forbidding second-phase codes during boot, and vice versa, using a volatile register to trigger phase transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If codes are stored in a single zone in non-volatile memory, then storage simplicity is improved, but security against malicious code execution is worsened
Solution Approach 1:
The non-volatile memory is divided into multiple zones (first zone, second zone, third zone) with distinct access control rules. The access control circuit segregates these zones to prevent malicious code execution during boot phase while allowing code storage and updates in later phases. This segmentation resolves the contradiction by maintaining simple storage structure while implementing security through zone-based access control.
2Reliability
If access control circuit forbids execution of codes in second zone during first phase, then boot security is improved, but code flexibility is worsened
Solution Approach 1:
The access control circuit dynamically changes access permissions based on the boot phase. During first phase, execution is forbidden in second zone; during second phase, execution is permitted. This dynamic adaptation resolves the contradiction by providing strict security during critical boot phase while enabling code flexibility during application phase through phase-dependent access control rules.
Solution Approach 2:
The system performs preliminary security enforcement during the first phase by forbidding execution in the second zone before any code loading or updates can occur. This preliminary action ensures that malicious codes cannot be executed during the critical initial boot process, while still allowing flexible code operations in the second phase after security validation.
3Reliability
If access control circuit forbids any access to first zone during second phase, then security against code injection is improved, but system functionality is worsened
Solution Approach 1:
The access control circuit applies different access rules to different zones based on their security requirements. The first zone (containing critical boot codes) has restricted access during second phase, while the second and third zones maintain full accessibility for code loading and updates. This localized quality control resolves the contradiction by protecting critical areas without compromising overall system functionality.
Data Source
AI summary
In an embodiment a method includes executing, during a first phase, one or more first codes stored in a first immutable zone of a non-volatile memory of an electronic device, forbidding, by an access control circuit of the non-volatile memory, execution of any codes stored in a second zone of the non-volatile memory during the first phase, executing, during a second phase, one or more second codes stored in the second zone and forbidding, by the access control circuit, any access to the first zone during the second phase.