Store-to-load forwarding physical address proxy matching
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Solution Overview
Problem
High-performance microprocessors face challenges in preventing side channel attacks (SCAs) without lengthening the execution pipeline or sacrificing performance, as conventional processors rely on speculative execution which creates vulnerabilities through incomplete physical address comparisons and time-consuming tablewalks.
Innovation Solution
Implementing a high-performance, speculative out-of-order executing super-scalar processor with a short execution pipeline that conditions store-to-load forwarding on complete physical address matching, using physical address proxies (PaPs) to speed up comparisons and reduce the number of bits compared, and incorporating a memory dependence predictor to minimize delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If speculative execution is used to enhance performance, then processing speed is improved, but vulnerability to side channel attacks increases
Solution Approach 1:
The patent performs preliminary physical address comparison and permission validation before speculative store-to-load forwarding occurs. By checking whether the physical addresses match and permissions are valid in advance, the system can safely speculate on data forwarding without creating security vulnerabilities. This preliminary validation prevents mis-speculation that could lead to side channel attacks while maintaining performance benefits.
2Reliability
If complete physical address comparison is performed before forwarding, then security is improved, but execution pipeline length increases
Solution Approach 1:
The patent extracts the critical security-checking functions (physical address comparison and permission validation) from the main execution pipeline and performs them in parallel or out-of-order. This allows the essential security validations to occur without forcing sequential execution and pipeline lengthening, maintaining both security and performance.
3Measurement precision
If physical address comparison is performed before forwarding, then accuracy of forwarding is improved, but time consumption increases
Solution Approach 1:
The patent changes the parameter being compared from virtual addresses to physical addresses for the store-to-load forwarding decision. By using physical addresses (which are translated early in the pipeline) and permission bits, the system achieves accurate address matching without the time penalty of waiting for complete tablewalk operations, as the physical address is available earlier than the final virtual address translation.
Data Source
AI summary
A method and system for mitigating against side channel attacks (SCA) that exploit speculative store-to-load forwarding is described. The method comprises ensuring that the physical load and store addresses match and/or that permissions are present before speculatively store-to-load forwarding. Various improvements maintain a short load-store pipeline, including usage of a virtual level-one data cache (DL1), usage of an inclusive physical level-two data cache (DL2), storage and lookup of physical data address equivalents in the DL1, and using a memory dependence predictor (MDP) to speed up or replace store queue camming of load data addresses against store data addresses.