Microprocessor MSR Fuse-Based Protection Configuration
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Solution Overview
Problem
Microprocessor manufacturers face challenges in accurately identifying and managing access to model-specific registers (MSRs) post-fabrication, leading to potential revenue loss due to incorrect password protection subsets, as the selection of protected MSRs is hardcoded and cannot be altered after manufacturing.
Innovation Solution
Incorporating a fuse associated with each MSR that can be blown to toggle its protection status, allowing for dynamic adjustment of password protection post-fabrication, enabling microcode to manage access based on the fuse state and default protection values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the subset of password-protected MSRs is hardcoded at fabrication time, then the microprocessor structure is simple and reliable, but the manufacturer cannot correct mistakes in MSR protection selection after fabrication
Solution Approach 1:
The patent applies the dynamics principle by transforming the static, hardcoded MSR protection configuration into a dynamic, changeable configuration. Fuses are introduced that can be blown during or after fabrication to toggle the protection state of individual MSRs. This allows the protection configuration to adapt from being fixed at fabrication time to being modifiable in subsequent manufacturing steps or even after the processor is deployed, resolving the contradiction between reliability of fixed configuration and flexibility to correct mistakes.
Solution Approach 2:
The patent applies parameter changes by using fuse states (blown或未blown) to change the protection parameter of MSRs. Each fuse is associated with a specific MSR and its state determines whether that MSR is password-protected or not. This mechanism allows the protection parameter to be changed from a fixed fabrication-time setting to a modifiable parameter that can be adjusted based on manufacturer needs, enabling correction of errors without discarding fabricated parts.
2Reliability
If password protection is applied to all MSRs by default, then security is improved, but the complexity of managing and configuring protection increases
Solution Approach 1:
The patent applies segmentation by dividing the MSR protection management into individual, independent units. Instead of applying a single blanket protection policy to all MSRs, the system segments protection control at the individual MSR level. Each MSR has its own associated fuse that can be independently controlled. This segmentation allows the manufacturer to selectively protect only specific MSRs that require security, while leaving others accessible, thereby reducing overall management complexity while maintaining security where needed.
Solution Approach 2:
The patent introduces fuses as intermediary elements between the MSR and the protection mechanism. These fuses act as mediators that simplify the protection management process. Rather than requiring complex software-based access control systems for each MSR, the fuse serves as a simple hardware intermediary that encodes the protection state. This intermediary approach reduces the complexity of managing MSR protection by providing a straightforward, hardware-level switching mechanism that can be controlled during manufacturing without requiring complex configuration software.
3Reliability
If the number of password-protected MSRs increases, then security coverage is improved, but the probability of selecting the wrong subset of MSRs to protect increases
Solution Approach 1:
The patent applies segmentation by providing individual fuse control for each MSR, allowing precise selection of which MSRs to protect. Instead of relying on predetermined hardcoded subsets that may be incorrect, the segmented approach enables the manufacturer to individually configure protection for each MSR based on actual security needs. This segmentation improves manufacturing precision in protection selection by allowing granular control rather than relying on coarse, pre-determined groups, thereby reducing the probability of selecting the wrong subset while maintaining comprehensive security coverage.
Data Source
AI summary
A microprocessor having model specific registers (MSRs) includes, for each of the MSRs, an associated default value that indicates whether the MSR is protected or non-protected and an associated fuse that, if blown, toggles the associated default value from protected to non-protected or non-protected to protected. In one embodiment, microcode that does the following in response to the microprocessor encountering an instruction that accesses a specified MSR: determines whether the fuse associated with the specified MSR is blown or unblown, uses the default value associated with the MSR as an indicator of whether the MSR is protected if the associated fuse is unblown; toggles the associated default value to generate the indicator if the associated fuse is blown; protects access to the MSR if the indicator indicates the MSR is protected; and refrains from protecting access to the MSR if the indicator indicates the MSR is non-protected.