Present but Unreachable: Reducing Persistentlatent Secrets in HotSpot JVM

Applications that manage \ sensitive secrets, including cryptographic keys, are typically \ engineered to overwrite the secrets in memory once they\u27re no longer \ necessary, offering an important defense against forensic attacks \ against the computer. In a modern garbage-collected memory system, \ however, live objects will be copied and compacted into new memory \ pages, with the user program being unable to reach and zero out \ obsolete copies in old memory pages that have not yet \ been reused. This paper considers this problem in the HotSpot JVM, \ the default JVM used by the Oracle and OpenJDK Java platforms. \ We analyze the SerialGC and Garbage First Garbage Collector (G1GC) \ implementations, showing that sensitive data such as TLS keys are \ easily extracted from the garbage. To mitigate this issue, we \ implemented techniques to sanitize older heap pages and we measure \ the performance impact--sometimes good, sometimes unacceptable. We \ also discuss how future garbage collectors might be designed from \ scratch with efficient heap sanitation in mind.