Revocation Pipeline for Invalidating Dangling Pointers in Memory
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Solution Overview
Problem
Existing methods for enhancing temporal memory safety in memory constrained systems face challenges in efficiently invalidating pointers to deallocated memory without introducing significant performance loss or stalling the central processing unit (CPU).
Innovation Solution
A hardware revocation engine with a revocation pipeline is introduced, which operates in conjunction with the main processor pipeline to efficiently invalidate pointers to deallocated memory by using a two-stage pipeline configuration that shares memory access, allowing low-latency scanning without CPU stalling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hardware revocation pipeline is introduced to invalidate pointers to deallocated memory, then temporal memory safety is improved, but device complexity increases
Solution Approach 1:
The memory validation function is segmented into multiple pipeline stages (fetch stage, validate stage, execute stage) that process pointer validations in parallel. Each stage handles a specific aspect of pointer validation, allowing the system to maintain high reliability while distributing complexity across modular components rather than concentrating it in a single complex unit.
Solution Approach 2:
A dedicated hardware revocation engine is introduced as an intermediary component between the main processor and memory. This intermediary handles the complex task of pointer validation independently, allowing the main processor to continue executing instructions without being directly burdened by the complexity of memory safety checks.
2Reliability
If memory scanning is performed to invalidate pointers, then temporal memory safety is improved, but processing speed decreases
Solution Approach 1:
The three-stage pipeline enables continuous pointer validation by overlapping the fetch, validate, and execute operations. While one pointer is being validated in the validate stage, the next pointer is being fetched in parallel, and the previous pointer's validation result is being executed. This continuous pipeline operation maintains high processing speed while ensuring thorough memory safety checks.
Solution Approach 2:
The validate stage performs preliminary validation of pointer addresses against the deallocation bitmap before the execute stage commits memory operations. This preliminary check prevents invalid memory access early in the pipeline, ensuring safety without requiring the main processor to stall and wait for complete validation before proceeding with instruction execution.
3Productivity
If a two-stage pipeline is used for pointer validation, then processing throughput is improved, but latency increases
Solution Approach 1:
The patent extends the two-stage pipeline to a three-stage pipeline, adding temporal dimension to the validation process. By distributing validation across three distinct time stages (fetch, validate, execute) rather than two, the system achieves better balance between throughput and latency, as each stage can operate more independently and parallelize more effectively with other pipeline operations.
4Use of energy by moving object
If the revocation pipeline shares memory access with the main processor, then memory bandwidth utilization is improved, but access conflict increases
Solution Approach 1:
Memory access is segmented into distinct phases corresponding to the pipeline stages. The fetch stage accesses memory for pointer values, while the validate stage accesses memory for bitmap data, and the execute stage writes validation results. This segmentation of memory access patterns reduces conflicts by organizing simultaneous accesses into structured, non-overlapping operations.
Solution Approach 2:
The revocation pipeline operates in periodic cycles, systematically progressing through the fetch, validate, and execute stages in repeated sequences. This periodic operation pattern allows the pipeline to rhythmically share memory bandwidth with the main processor, predicting and managing access conflicts through regular, predictable timing rather than random simultaneous accesses.
Data Source
AI summary
A hardware revocation engine for invalidating a pointer, that refers to a deallocated object, from memory in a memory constrained system. The hardware revocation engine has a revocation pipeline coupled to a pipeline of a main processor of the memory constrained system. The revocation pipeline shares access to memory with the main pipeline, the revocation pipeline comprising at least a first stage and a subsequent second stage. In a first cycle of the revocation pipeline, the first stage of the revocation pipeline loads a first pointer-sized value from the memory. In a second cycle: the second stage checks whether the first loaded pointer-sized value is a pointer referring to deallocated memory. In a third cycle: in response to the outcome of the check indicating that the first loaded pointer-sized value is a pointer referring to deallocated memory, the first stage invalidates the first pointer-sized value.