BIOS Memory Scrub Control via Shutdown MOR Bit Clearing
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Solution Overview
Problem
Existing computer systems unnecessarily perform memory scrubs during each boot process due to a persistently set memory override (MOR) bit, causing boot delays and user inconvenience, as they lack sophisticated control over when memory scrubs occur.
Innovation Solution
Implementing a system that allows memory scrubs to be selectively performed during shutdown processes, clearing the MOR bit to prevent subsequent boot process scrubs, and using a memory scrub indicator to inform users of scrub status, even when video drivers are unavailable, through a combination of BIOS, I/O bridge, and TPM components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the MOR bit is maintained in a set condition to prevent reset or power cycle attacks, then security is improved, but unnecessary memory scrubs are performed during each boot process causing boot delays
Solution Approach 1:
The patent implements dynamic control of the MOR bit, transitioning it from a static persistent state to a conditional state that changes based on shutdown events. The MOR bit is cleared during shutdown processes, allowing the system to adapt its security posture dynamically rather than maintaining a fixed state, thereby preventing unnecessary memory scrubs during boot while preserving security when needed.
Solution Approach 2:
The patent performs memory scrubs during the shutdown process rather than during boot. By completing the scrubbing action in advance (during shutdown), the system ensures security is maintained without causing delays during the subsequent boot process, effectively decoupling the security function from the boot time constraint.
2Reliability
If memory scrubs are performed during boot process to ensure secrets are deleted, then security is improved, but user perception of system responsiveness deteriorates due to boot delays
Solution Approach 1:
The patent performs the memory scrubbing operation during the shutdown process as a preliminary action before the next boot cycle begins. This timing ensures that security maintenance is completed without interfering with the user's boot experience, as the scrubbing occurs during the transition period rather than during the visible boot process.
Solution Approach 2:
The shutdown process acts as an intermediary timing mechanism that separates the security-critical memory scrubbing operation from the user-visible boot process. By using shutdown as the intermediary timing window, the system can perform maintenance tasks without directly impacting user-perceived responsiveness during boot.
3Reliability
If the MOR bit is set to trigger memory scrubs, then security against reset attacks is improved, but system complexity increases due to additional control mechanisms
Solution Approach 1:
The patent implements self-service by having the shutdown process automatically clear the MOR bit as part of its standard operation. Rather than requiring separate complex control logic to manage MOR bit state, the system uses the existing shutdown mechanism to perform the clearing action, reducing overall system complexity while maintaining security functionality.
Data Source
AI summary
A computer system is provided, the computer system having a processor and a system memory coupled to the processor. The computer system also includes a Basic Input/Output System (BIOS) in communication with the processor. The BIOS selectively scrubs the system memory during a shutdown process of the computer system.