Boot Code Integrity via Hardware Write Locking
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Solution Overview
Problem
Electronic devices are vulnerable to attacks through malicious code and physical modifications, which can compromise their security and integrity, particularly affecting boot code and operating systems.
Innovation Solution
Implementing trusted boot code, hardware write locking of non-volatile memory regions, and redundant code versions to ensure self-recovery and protect against unauthorized modifications, using a memory controller to manage access and validate code integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware write locking is implemented to protect code regions, then security against unauthorized modifications is improved, but device complexity increases due to additional memory management mechanisms
Solution Approach 1:
The non-volatile memory is divided into multiple regions with different access permissions: a first region for boot code with write-lock protection, a second region for operating system code, and a third region for application code. This segmentation allows selective protection of critical code while maintaining manageability of the overall system.
Solution Approach 2:
The boot code is executed first before the operating system and applications, and it performs the write-lock protection setup for critical memory regions. This preliminary action ensures that security measures are in place before higher-level code can potentially compromise them.
2Reliability
If redundant code versions are stored in memory, then self-recovery capability from corruption is improved, but memory usage increases
Solution Approach 1:
Redundant copies of critical code (such as boot code) are stored in protected memory regions. If the primary code becomes corrupted, the system can detect the corruption and switch to executing from the redundant copy, enabling self-recovery without external intervention.
Solution Approach 2:
The system changes the operational state by switching between different code versions stored in memory. When corruption is detected, the execution source changes from the primary code region to the redundant code region, maintaining system functionality despite the corruption event.
3Reliability
If boot code validates operating system code before execution, then security against malicious code is improved, but boot time increases
Solution Approach 1:
The boot code performs validation of the operating system code during the boot process before transferring execution control. This preliminary validation ensures that only authenticated, uncorrupted code is executed, preventing malicious code from compromising the system.
Solution Approach 2:
The patent replaces physical security measures (such as secure hardware enclaves or tamper-proof sealing) with cryptographic validation mechanisms. The boot code uses digital signatures and hash functions to verify code integrity, substituting mechanical security with software-based cryptographic verification.
4Reliability
If memory regions are protected from writing, then code integrity is improved, but ease of code updates deteriorates
Solution Approach 1:
The memory system is segmented into protected regions for critical code (boot code, OS) and updateable regions for applications and configuration data. This segmentation allows the critical portions to maintain integrity through write-lock protection while permitting updates to non-critical portions through controlled mechanisms.
Solution Approach 2:
The write-protection status of memory regions is made dynamic rather than static. The boot code can selectively enable or disable write protection for different regions based on their current state and update requirements, allowing flexible management of code integrity and updatability.
Data Source
AI summary
In some examples, in response to a reset of an electronic device, a method disables hardware write locking of a first region in a non-volatile memory, and executes a first boot code portion from the first region to begin a boot procedure. The executed first boot code portion checks whether an update code for the first boot code portion exists. In response to determining that no update code for the first boot code portion exists, the executed first boot code portion causes hardware write locking of the first region. After causing the hardware write locking of the first region, the boot procedure continues, the boot procedure comprising verifying an integrity of a second boot code portion.