CPU-Based Measured Boot Using Command Buffer
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Solution Overview
Problem
The existing measured boot process in computer systems lacks scrutiny of the Core Root of Trust for Measurement (CRTM), which can be vulnerable to attacks, and initializing a hardware-based CRTM is inefficient due to complex TPM protocols and timing constraints.
Innovation Solution
Implementing a CPU-based measured boot process where the CPU initializes and takes measurements before the TPM is fully operational, using a command buffer to store these measurements prior to TPM initialization, thereby enabling the CPU's microcode to serve as a secure CRTM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hardware-based CRTM is implemented using TPM, then security is improved, but initialization time and complexity increase
Solution Approach 1:
The patent performs measurement actions before the TPM is fully initialized. The CPU takes measurements of boot components and stores them in a buffer memory location before the TPM firmware is loaded, then transfers these pre-captured measurements to the TPM after initialization. This preliminary action resolves the timing conflict between CPU initialization and TPM readiness.
Solution Approach 2:
The patent introduces a buffer memory location as an intermediary between the CPU and TPM. This buffer serves as a temporary storage mechanism that decouples the measurement capture phase (before TPM initialization) from the measurement storage phase (after TPM initialization), allowing the system to bridge the timing gap without requiring complex protocol handshaking.
2Reliability
If TPM firmware is loaded and initialized before storing measurements, then TPM operational reliability is ensured, but the CPU cannot establish measurements in time
Solution Approach 1:
The CPU performs the measurement action in advance before the TPM is operational. The measurement of boot components is captured and held in a buffer memory location during the TPM initialization sequence, ensuring that when the TPM becomes operational, the measurements are already ready for transfer and storage.
Solution Approach 2:
The measurement process is segmented into two distinct phases: (1) measurement capture phase where the CPU takes measurements and stores them in buffer memory before TPM initialization, and (2) measurement transfer phase where the pre-captured measurements are transferred to the TPM after initialization. This segmentation allows each phase to proceed independently without blocking the other.
3Ease of manufacture
If a software-based CRTM is used in BIOS, then ease of implementation is improved, but vulnerability to root kits and malware increases
Solution Approach 1:
The buffer memory location acts as an intermediary that enables the CPU to perform measurement functions traditionally associated with the TPM. This allows the system to use the CPU as the Core Root of Trust while still utilizing the TPM for secure measurement storage, combining the implementation ease of software-based approaches with the security benefits of hardware-based verification.
Data Source
AI summary
A measured boot process for an electronic device includes taking a measurement of the early system start up instructions of the electronic device upon a reboot or start-up of the device. A representation of the measurement is stored in a trusted platform module of the electronic device prior to initialization of the trusted platform module. Access is granted to the representation of the measurement stored in the trusted platform module prior to initialization of the trusted platform module thereby enabling the representation of the measurement to serve as the core root of trust for measurement.