Access Filter for Secure Firmware State Management
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Solution Overview
Problem
Existing secure processing systems face vulnerabilities as physical separation alone is insufficient to prevent unauthorized access to sensitive code and data, particularly during firmware switching operations, which can compromise hardware resources.
Innovation Solution
A processing system incorporating a processor, memory, a state machine, and an access filter that transitions between predefined states to selectively control and filter hardware access transactions, ensuring that only authorized firmware can access specific code and data, thereby preventing unauthorized access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If physical separation is used to isolate the security subsystem, then hardware isolation is improved, but security against malicious code in the external environment is insufficient
Solution Approach 1:
The patent divides the security subsystem into distinct operational states (secure boot state, runtime security state, etc.) using a state machine. Each state has specific access permissions defined in an access filter, preventing malicious code from accessing sensitive resources regardless of physical separation. This segmentation of operational states complements the physical separation to provide layered security.
Solution Approach 2:
The access filter acts as an intermediary between the security subsystem and external environment. It mediates all access requests by checking the current state machine state against predefined access rules, blocking malicious code attempts while allowing legitimate operations. This intermediary layer bridges the gap between physical separation and logical security enforcement.
2Adaptability or versatility
If firmware switching operations are allowed, then system functionality is improved, but vulnerability to compromised firmware accessing other firmware increases
Solution Approach 1:
The access filter is pre-configured with state-specific access rules before firmware switching occurs. When the state machine transitions to a new state, the corresponding access filter rules are automatically applied, preventing compromised firmware from accessing other firmware or data. This preliminary configuration of access permissions addresses the vulnerability before it can be exploited.
Solution Approach 2:
The access filter dynamically adjusts permissions based on the current state machine state. During firmware switching operations, the state transitions trigger corresponding changes in access permissions, allowing legitimate firmware switching while blocking unauthorized access attempts. This dynamic adaptation enables functionality while mitigating security risks.
3Reliability
If access filtering based on state machine is implemented, then security against unauthorized access is improved, but device complexity increases
Solution Approach 1:
The access filter and state machine are merged into an integrated security mechanism within the security subsystem. The state machine's current state directly determines the access permissions in the access filter, creating a unified system that provides strong security without requiring separate complex control structures. This merging reduces overall system complexity while maintaining high security.
Data Source
AI summary
A processing system including a processor, a first memory, a state machine configured to transition between a plurality of states, and an access filter. The first memory stores instructions that are executable by the processor, where execution of the instructions causes the processor to initiate transactions with one or more hardware resources. The access filter may filter the transactions initiated by the processor by selectively denying access to the hardware resources based at least in part on a current state of the state machine. The access filter may also filter transactions initiated by one or more of the hardware resources based at least in part on the current state of the state machine.