Microsoft and Google are jointly disclosing a new CPU security vulnerability that’s similar to the Meltdown and Spectre flaws that were revealed earlier this year. Labelled Speculative Store Bypass (variant 4), the latest vulnerability is a similar exploit to Spectre and exploits speculative execution “that modern CPUs use. Browsers like Safari, Edge, and Chrome were all patched for Meltdown earlier this year, and Intel says these mitigations are also applicable to variant 4 and available for consumers to use today.”
However, unlike Meltdown (and more similar to Spectre) this new vulnerability will also include firmware updates for CPUs that could affect performance. Intel has already delivered microcode updates for Speculative Store Bypass in beta form to OEMs, and the company expects them to be more broadly available in the coming weeks. The firmware updates will set the Speculative Store Bypass protection to off-by-default, ensuring that most people won’t see negative performance impacts.
This cat ain’t going back in no bag anytime soon.
Speculative execution is taking a beating. I knew from the start that spectre wouldn’t be the end of it. By the time we’re done we might just conclude that speculative execution is too insecure for hardened systems.
It’s not all bad news though, if we nix these long speculative pipelines in superscaller CPUs, suddenly that frees up tons of space on the CPU die to do bigger and better things with. Single threaded performance will regress, but we could make progress in other areas like VLIW. Given how prevalent vector algorithms have become, I would welcome such a development.