I/O MMU Policy-Based DMA Control for Restricted Mode Security
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Solution Overview
Problem
Existing computer architectures face challenges in restricting peripheral device access to memory, particularly with DMA-enabled devices, which can compromise security by allowing unauthorized alterations or replacements of security programs during restricted operation modes.
Innovation Solution
Implementing an I/O MMU with a policy-based direct memory access control system that pairs virtual memory addresses with physical locations, using an I/O TLB to manage access and deny DMA access to unauthorized peripherals while allowing trusted devices to access main memory, thereby enforcing restricted operation modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DMA access is allowed for peripheral devices, then operational efficiency and device functionality are improved, but security vulnerability increases allowing unauthorized memory access
Solution Approach 1:
The patent introduces an I/O MMU as an intermediary device between peripheral devices and main memory. This mediator translates I/O virtual addresses to physical addresses while enforcing access control policies, allowing DMA operations to proceed efficiently for authorized devices while blocking unauthorized access attempts, thus resolving the security vulnerability without sacrificing operational efficiency
Solution Approach 2:
The patent segments memory access control by creating separate address spaces and access policies for different peripheral devices. The I/O MMU maintains device-specific page tables and access rights, allowing each peripheral to have customized DMA permissions. This segmentation enables selective authorization where only trusted devices can access specific memory regions, preventing unauthorized modifications while maintaining efficient DMA for approved devices
2Object-affected harmful factors
If DMA access is restricted for security, then security vulnerability is reduced, but operational functionality deteriorates
Solution Approach 1:
The patent implements dynamic access control where the I/O MMU can modify DMA permissions based on operational context. Access policies are not static but can be adjusted according to system state, user authentication level, and device trust status. This dynamic approach allows the system to enforce strict security when needed while permitting full operational functionality when security risks are mitigated, resolving the contradiction between security restriction and functional versatility
3Speed
If I/O TLB is used for address translation, then address mapping efficiency is improved, but memory access control complexity increases
Solution Approach 1:
The patent merges the address translation function with the access control function within the I/O MMU. The I/O TLB is integrated into the same hardware structure that enforces DMA policies, combining two functions into a single unified device. This integration allows address translation and access control to occur simultaneously in a single hardware stage, improving speed while managing complexity through functional consolidation rather than separate independent components
Data Source
AI summary
A computer that operates in a metered mode for normal use and a restricted mode uses an input/output memory management unit (I/O MMU) in conjunction with a security policy to determine which peripheral devices are allowed direct memory access during the restricted mode of operation. During restricted mode operation, non-authorized peripheral devices are removed from virtual address page tables or given vectors to non-functioning memory areas.