Meltdown fundamentally changes our perspective on the Security of Hardware Optimizations that change the state of microarchitectural elements. Meltdown and Spectre teach us that functional correctness is insufficient for security analysis and the micro-architecture cannot be ignored. They further open a new field of research to investigate the extent to which performance optimizations change the microarchitectural state, how this state can be lifted into an architectural state, and how such attacks can be prevented. Without requiring any software vulnerability and independent of the operating system, Meltdown enables an adversary to read sensitive data of other processes, containers, virtual machines, or the kernel. CACM, “Meltdown: Reading Kernel Memory from User Space”
Security of Hardware Optimizations is simply the mindful consideration of the security implications of hardware optimizations. That is, hardware optimizations provide significant benefits. However, those based on e.g. microarchitectural elements have potential adverse side effects such as data leakage that is taken advantage of in Meltdown vulnerability attacks.