DRAM Word-Line Protection Using Randomized Refresh Selection
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Solution Overview
Problem
Dynamic random access memory (DRAM) systems face the security issue of row hammer, where unintended charge leakage between memory rows due to repeated access patterns can alter nearby memory content, potentially causing 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, using logic gates and a switch to increase unpredictability, and a number trimmer to ensure the number stays within the maximum activations between refresh cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional DRAM refresh cycles are used without protection mechanisms, then memory access speed is maintained, but row hammer attacks can cause charge leakage and data corruption in adjacent word lines
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-protects adjacent word lines that are susceptible to charge leakage, rather than waiting for actual corruption to happen. This is implemented through the vulnerable word line identification circuit that continuously analyzes access patterns and triggers protection in advance.
Solution Approach 2:
The patent introduces intermediary components between the normal memory access path and the word lines. These include the vulnerable word line identification circuit, protection status storage circuit, and word line protection circuit that act as mediators to detect, decide, and execute protection actions. These intermediary circuits intercept access patterns, determine vulnerability, and apply protection without disrupting normal memory operations.
2Reliability
If random number generation logic gates and switches are added to select protected word lines, then unpredictability against row hammer attacks is improved, but device complexity increases
Solution Approach 1:
The patent changes the parameter of word line selection from deterministic to random. By introducing random number generation through logic gates (XOR, AND, OR) and switches, the system dynamically varies which word lines are protected based on generated random values. This parameter change makes it unpredictable which adjacent word lines will be protected, effectively countering row hammer attacks that rely on predictable access patterns.
3Reliability
If adjacent word lines are protected during refresh cycles, then charge leakage is prevented, but refresh operation time increases
Solution Approach 1:
The patent applies local quality by providing differentiated treatment to different word lines based on their vulnerability. Instead of uniformly protecting all word lines during refresh cycles, the system selectively protects only those adjacent word lines that are identified as vulnerable to row hammer attacks. This localized protection approach minimizes the impact on refresh cycle duration while maintaining charge retention for susceptible word lines.
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.