DRAM Word-Line Protection with Randomized Refresh for Row Hammer
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Solution Overview
Problem
Dynamic random access memory (DRAM) systems face the row hammer security issue where memory cells interact electrically, causing unintended charge leakage in adjacent memory rows, which can be exploited by malicious operators to change content, leading to device malfunction.
Innovation Solution
A memory device with a protection circuit that includes 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, ensuring the counter counts down within a predetermined activation limit to refresh adjacent word lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DRAM systems perform periodic refresh cycles to maintain charge in capacitors, then data retention is improved, but adjacent word lines are vulnerable to row hammer attacks causing unintended charge leakage
Solution Approach 1:
The protection circuit performs preliminary actions by refreshing adjacent word lines before they are actually attacked. The counter monitors activation counts of word lines, and when a threshold is reached, the circuit proactively refreshes adjacent word lines to prevent row hammer effects, rather than waiting for damage to occur.
Solution Approach 2:
The protection circuit implements feedback by continuously monitoring the activation count of word lines through the counter. When the activation count exceeds the threshold, the circuit generates a protection signal to refresh adjacent word lines. This closed-loop feedback mechanism ensures that protection actions are triggered based on actual usage patterns, preventing charge leakage while maintaining data retention.
2Productivity
If the same word line is activated multiple times to access data, then data retrieval is improved, but row hammer effect is triggered causing charge leakage in adjacent word lines
Solution Approach 1:
The protection circuit converts the harmful row hammer effect into a beneficial protection mechanism. By monitoring activation counts and using the counter to trigger refresh operations on adjacent word lines, the circuit transforms the vulnerability caused by repeated activations into a protective feature that prevents charge leakage while maintaining normal data access operations.
Solution Approach 2:
The circuit performs preliminary protection by refreshing adjacent word lines before they are attacked. The counter monitors activation patterns, and when the threshold is approached, the protection circuit proactively refreshes adjacent word lines to prevent row hammer effects, rather than waiting for damage to occur.
3Reliability
If all word lines are refreshed during each refresh cycle, then data integrity is improved, but memory access time and energy consumption increase
Solution Approach 1:
The protection circuit applies local quality by selectively refreshing only adjacent word lines that are vulnerable to row hammer attacks, rather than refreshing all word lines uniformly. This targeted approach maintains data integrity for protected word lines while reducing the overall time and energy consumption associated with comprehensive refresh operations.
Solution Approach 2:
The circuit performs partial action by refreshing only the necessary adjacent word lines that are at risk of row hammer effects, rather than performing excessive full refresh operations on all word lines. This partial refresh strategy maintains data integrity for critical word lines while optimizing memory access time and energy consumption.
4Reliability
If a protection mechanism is added to prevent row hammer attacks, then security is improved, but device complexity increases
Solution Approach 1:
The protection circuit achieves universality by integrating multiple functions into a single circuit structure. The counter serves both as an activation count monitor and as a trigger for protection operations. The circuit combines monitoring, decision-making, and execution functions in one unified structure, reducing overall device complexity while maintaining security against row hammer attacks.
Solution Approach 2:
The protection circuit implements self-service by automatically monitoring activation counts and triggering protection operations without external intervention. The counter continuously tracks word line activations, and when the threshold is reached, the circuit autonomously generates protection signals to refresh adjacent word lines, eliminating the need for complex external control mechanisms.
Data Source
AI summary
A memory device and a method for protecting the same are provided. The memory device includes a controller configured to refresh a first word line and a first protected word line during a first refresh cycle in response to a refresh signal, a random number generator configured to receive an address of the first word line and an address of the first protected word line to generate a first number, a counter electrically coupled to the random number generator. The counter is configured to receive the first number as an initial value of the counter, and configured to be turned on in response to the refresh signal. 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 a second protected word line, adjacent to the second accessed word line, during a second refresh cycle.