Benchmarking The Linux Mitigated Performance For Retbleed: It's Painful

Yesterday Retbleed was made public as a new speculative execution attack exploiting return instructions. While the "good" news is Retbleed only impacts prior generations of AMD and Intel processors, the bad news is the mitigated performance impact on Linux is quite severe. Since yesterday I have been benchmarking the newly-merged Linux patches on various Intel and AMD processors affected by Retbleed. It's very bad if you are on an affected processor.