Apple M1 GPUs retain register file data between compute shader dispatches from different…

Summary

Apple M1 GPUs retain register file data between compute shader dispatches from different processes. A sandboxed Metal attacker app can run a GPU reader shader that reads stale register values left by a separate sandboxed victim app. In the proof of concept, GPUVictim.app generates a fresh random 128-bit secret using SecRandomCopyBytes and loads it into GPU registers. GPUAttacker.app, a separate sandboxed app, recovers the exact secret from stale GPU register state. NOTE: The vendor stated that this behavior affects only legacy hardware and has already been addressed at the hardware level in current-generation Apple Silicon.