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Increasing single-cell DRAM error rates have pushed DRAM manufacturers toadopt on-die error-correction coding (ECC), which operates entirely within aDRAM chip to improve factory yield. The on-die ECC function and its effects onDRAM reliability are considered trade secrets, so only the manufacturer knowsprecisely how on-die ECC alters the externally-visible reliabilitycharacteristics. Consequently, on-die ECC obstructs third-party DRAM customers(e.g., test engineers, experimental researchers), who typically design, test,and validate systems based on these characteristics.  To give third parties insight into precisely how on-die ECC transforms DRAMerror patterns during error correction, we introduce Bit-Exact ECC Recovery(BEER), a new methodology for determining the full DRAM on-die ECC function(i.e., its parity-check matrix) without hardware tools, prerequisite knowledgeabout the DRAM chip or on-die ECC mechanism, or access to ECC metadata (e.g.,error syndromes, parity information). BEER exploits the key insight thatnon-intrusively inducing data-retention errors with carefully-crafted testpatterns reveals behavior that is unique to a specific ECC function.  We use BEER to identify the ECC functions of 80 real LPDDR4 DRAM chips withon-die ECC from three major DRAM manufacturers. We evaluate BEER's correctnessin simulation and performance on a real system to show that BEER is effectiveand practical across a wide range of on-die ECC functions. To demonstrateBEER's value, we propose and discuss several ways that third parties can useBEER to improve their design and testing practices. As a concrete example, weintroduce and evaluate BEEP, the first error profiling methodology that usesthe known on-die ECC function to recover the number and bit-exact locations ofunobservable raw bit errors responsible for observable post-correction errors.

Bit-Exact ECC Recovery (BEER): Determining DRAM On-Die ECC Functions by Exploiting DRAM Data Retention Characteristics