Secure Operating Mode for Computing Devices
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Solution Overview
Problem
Lock screens on computing devices can be circumvented by external devices through methods like DMA attacks or mimicking peripherals, which compromise security by allowing unauthorized access.
Innovation Solution
Implementing a secure operating mode that activates when a 'lock' signal is received, using a communication interface controller to block malicious communications from external devices by referencing an alternative interrupt descriptor table that references safe or null instructions, thereby preventing unauthorized access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lock screen is implemented to protect the computing device, then security against unauthorized access is improved, but the lock screen can be circumvented by external devices through DMA attacks or peripheral mimicry
Solution Approach 1:
The patent segments the interrupt handling system into two distinct paths: a secure interrupt handler that references a secure interrupt descriptor table (IDT) and a non-secure interrupt handler that references a non-secure IDT. This segmentation isolates critical security functions from potential attacks, allowing the secure path to maintain security even when external devices attempt DMA attacks or peripheral mimicry, thereby resolving the contradiction between security and vulnerability to external attacks.
2Adaptability or versatility
If the computing device allows communication with external devices for normal operation, then device functionality and adaptability are improved, but malicious communications from external devices can compromise security
Solution Approach 1:
The patent introduces an intermediary mechanism in the form of the secure interrupt handler and secure IDT, which act as a mediator between external devices and the core processing unit. This intermediary verifies and filters interrupt requests, allowing legitimate communications from external devices while blocking malicious communications, thus maintaining both device adaptability and security against harmful factors.
3Device complexity
If the computing device processes all interrupt requests through a single interrupt handler, then device complexity is reduced, but security against DMA attacks and peripheral mimicry is compromised
Solution Approach 1:
The patent applies segmentation by dividing the interrupt handling structure into multiple distinct handlers (secure and non-secure) with separate interrupt descriptor tables. Although this increases structural complexity, it provides the necessary security differentiation to protect against DMA attacks and peripheral mimicry, resolving the contradiction between simplicity and security by showing that controlled complexity is necessary for security.
Data Source
AI summary
Example computing devices that are enabled to enter secure operating modes are provided. An example computing device includes a main processor to run an operating system enabled to establish communication from an external device to the main processor via a hardware interrupt handler when the external device is connected to the computing device. The computing device further includes a keyboard controller to detect a lock keystroke sequence at a keyboard, and, in response to detecting the lock keystroke sequence, cause the main processor to halt the operating system and to enter a secure operating mode in which communication from the external device to the main processor via the hardware interrupt handler is blocked.