Meltdown
A microarchitectural vulnerability that leaks privileged data through cache side effects left by transient execution before access faults retire.
Meltdown is not a persistent architectural permission bypass. A load that should fault can transiently influence microarchitectural state during out-of-order execution, and the attacker recovers that influence through cache timing.
Security Boundary
The vulnerability demonstrated that architectural state and microarchitectural state such as caches and translation structures do not share the same isolation guarantees. KPTI-style mitigations reduce exposure by separating kernel and user mappings more aggressively.
Performance impact depends on workload shape; syscall-heavy services and CPU-bound user code do not pay the same cost.
Source
- https://arxiv.org/abs/1801.01207
- https://nvd.nist.gov/vuln/detail/CVE-2017-5754