DRAM Word Line Protection Using Randomized Adjacent Row Refresh
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Solution Overview
Problem
Dynamic random access memory (DRAM) systems are vulnerable to the row hammer effect, where memory cells leak charges into adjacent rows, potentially altering their content, which can be exploited maliciously, leading to device malfunction.
Innovation Solution
A memory device with a protection circuit incorporating a random number generator and counter to randomly select and protect vulnerable word lines by generating a random number based on the last refreshed and accessed word line addresses, using logic gates and a switch to increase unpredictability, and a number trimmer to ensure the number stays within the refresh cycle limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional DRAM refresh cycles are used, then memory cells are periodically refreshed, but adjacent word lines remain vulnerable to row hammer attacks causing charge leakage and data alteration
Solution Approach 1:
The patent applies preliminary action by proactively identifying and protecting vulnerable word lines before row hammer attacks can occur. The system monitors access patterns and pre-refreshes adjacent word lines that are susceptible to charge leakage, preventing the harmful effect rather than reacting after damage occurs.
Solution Approach 2:
The patent introduces an intermediary protection mechanism between the vulnerable memory cells and the row hammer attack. This includes protection circuits that detect and block malicious access patterns, and refresh control logic that acts as a mediator to refresh protected word lines at appropriate times without disrupting normal memory operations.
2Reliability
If all word lines are refreshed in every refresh cycle, then data integrity is maintained, but memory bandwidth and performance are reduced
Solution Approach 1:
The patent applies local quality by differentiating between protected and unprotected word lines. Instead of uniformly refreshing all word lines, the system applies refresh operations selectively only to vulnerable adjacent word lines identified through access pattern monitoring, thereby maintaining data integrity where needed while preserving memory bandwidth for normal operations.
Solution Approach 2:
The patent implements partial action by performing refresh operations on only a subset of word lines that are actually vulnerable to row hammer attacks. This partial refresh approach is sufficient to protect against attacks while avoiding the performance penalty of refreshing all word lines, achieving the minimum necessary action for security.
3Measurement precision
If access patterns are monitored to identify vulnerable word lines, then protection accuracy is improved, but system complexity and overhead increase
Solution Approach 1:
The patent applies segmentation by dividing the monitoring function into distinct components: access pattern detection circuits that track memory accesses, vulnerability determination logic that identifies susceptible word lines, and refresh control mechanisms that execute protection. This segmentation allows each component to perform its specific function efficiently, managing overall system complexity.
Solution Approach 2:
The patent implements self-service through automatic vulnerability detection and protection mechanisms that operate without external intervention. The system autonomously monitors its own access patterns, identifies vulnerable word lines, and executes refresh operations, eliminating the need for complex external control systems while maintaining high detection accuracy.
Data Source
AI summary
A memory device and a method for protecting the same are provided. The memory device includes: a random number generator, a counter, and a controller. The random number generator includes a first logic gate and a second logic gate configured to generate a first output and a second output, respectively, according to the address of the first word line and the address of the first accessed word line. The random number generator further includes a switch configured to select one of the first output and the second output to be a first number. The counter is configured to receive the first number and count down from the first number. The controller is configured to obtain an address of a second accessed word line being accessed when the counter counts down to zero, and refresh adjacent word lines of the second accessed word line during a second refresh cycle.