Parent commenter might be thinking of Meltdown, a related architectural bug that only bit Intel and IBM PPC. Everything with speculative execution has Spectre[0

Parent commenter might be thinking of Meltdown, a related architectural bug that only bit Intel and IBM PPC. Everything with speculative execution has Spectre[0], but you only have Meltdown if you speculate across security boundaries. The reason why Meltdown has a more dramatic name than Spectre, despite being the same vulnerability, is that hardware privilege boundaries are the only defensible boundary against timing attacks. We already expect context switches to be expensive, so we're allowed to make them a little more expensive. It'd be prohibitively expensive to avoid leaking timing from, say, one executable library to a block of JIT compiled JavaScript code within the same browser content process. [0] https://randomascii.wordpress.com/2018/01/07/finding-a-cpu-design-bug-in-the-xbox-360/ https://randomascii.wordpress.com/2018/01/07/finding-a-cpu-d...