How Cloudflare is staying ahead of the AMD vulnerability known as “Zenbleed”

What this post added

This post details the mitigation of the 'Zenbleed' vulnerability (CVE-2023-20593) affecting AMD Zen 2 CPUs. It explains the vulnerability, which exploits speculative execution to leak data from AVX registers, and describes Cloudflare's response: patching the entire fleet of potentially impacted servers with AMD's microcode update. The post also provides background on CPU architecture, ALUs, registers, and Advanced Vector Extensions (AVX), as well as the technical details of the attack mechanism involving speculative execution and the `vzeroupper` instruction.