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Yes, I think that's what I said? Every attack no matter how deep it seemed to be has been patchable in microcode, sometimes at a cost in performance. But so far
by mike_hearn 3y ago
Yes, I think that's what I said? Every attack no matter how deep it seemed to be has been patchable in microcode, sometimes at a cost in performance. But so far nobody had to toss the physical silicon, at least not with Intel. The malleability of these chips is quite fascinating.
- rocqua 3y agoThe meltdown and spectre mitigations weren't patched in microcode, they were patched by changing the internal calling methods of the kernel.
- mike_hearn 3y agoI think it was both. There were initial software only patches, but those were quickly superseded by microcode+kernel patches, where microcode added features the kernel enabled. IBRS or something like that.
- cbsmith 3y agoIt was both, and none of them completely addressed the problem. They did need new hardware for that.
- sigotirandolas 3y agoOn some Skylake CPUs to get full mitigations you are taking a 30% performance penalty _and_ you need to disable SMT which is often another double digit penalty. It's not a literal "toss the physical silicon", but it's getting there. In fact my thesis is that it's never a literal "toss the physical silicon" because the kernel is able to take control when switching between tasks so (with help from the microcode) it's able to wipe all potential speculation vectors (at an arbitrarily expensive cost) before switching to the next task. This also explains why SMT is unfixably broken on some processors, since by design the kernel does not intervene in the task switching on the virtual cores.