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What is Target row refresh (TRR)?

One of the countermeasures against Rowhammer. Frequently activated rows are tracked and the rows next to them are refreshed earlier than usual to prevent bit flips. It is built into the DRAM or the memory controller. In-DRAM implementations often can track only a limited number of rows, and research has shown cases in which they were bypassed by activating many rows in turn.

Japanese name: TRR(ターゲットロウリフレッシュ)

Target row refresh (TRR) appears in 4 practice questions across 2 topics, including Hardware Security: Advanced Topics and Trends, DRAM.

Field: Hardware Security: Advanced Topics and Trends

Try it: questions about Target row refresh (TRR)

Which correctly explains why Rowhammer protection by in-DRAM TRR (target row refresh) has been bypassed in research?

  1. ATRR is a mechanism that stops refresh, so while TRR is active, bits in all rows actually become more likely to flip
  2. BTRR works by first disabling ECC, so every time TRR acts, uncorrectable errors increase and attacks exploit them
  3. CThe number of rows it can track is limited, so activating many rows leaves some unprotected, and flips could also occur in rows two rows away
Show answer and explanation

Answer: C. The number of rows it can track is limited, so activating many rows leaves some unprotected, and flips could also occur in rows two rows away

Because of circuit-area limits, many in-DRAM TRR implementations recorded only a few frequently activated rows and gave the rows next to them extra refreshes. TRRespass, published in 2020, showed that activating many rows in turn overwhelmed the records, so bits flipped in unprotected rows. Half-Double, published in 2021, showed that flips occur even in rows two rows away, and that the extra refreshes (activations) meant to protect the adjacent rows can themselves add to the interference on rows further out. These results led to calls for mechanisms that count activations of every row exactly and for layered countermeasures across the whole system.

Target row refresh (TRR) in the explanations

Questions that mention Target row refresh (TRR) (4)

  1. Which correctly explains why Rowhammer protection by in-DRAM TRR (target row refresh) has been bypassed in research?
  2. In DRAM, what is the phenomenon in which repeatedly activating one row in a short time can flip data in adjacent rows?
  3. What is wrong with the idea that "if ECC memory is used, there is no need to worry about Rowhammer"?
  4. Which correctly describes the idea of PRAC (per-row activation counting), added to the DDR5 standard updated in 2024 (JESD79-5C)?

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Related terms

Rowhammer DRAM (dynamic random-access memory) Refresh ECC (error-correcting code) Bank Arm CCA (Confidential Compute Architecture) CHERI Confidential computing Control-flow integrity DICE (Device Identifier Composition Engine)

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