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The "Retbleed" speculative execution vulnerabilities
Tuesday July 12, 2022. 07:11 PM , from LWN.net
Some researchers at ETH Zurich have disclosed a
new set of speculative-execution vulnerabilities known as 'Retbleed'. In short, the retpoline defenses added when Spectre was initially disclosed turn out to be insufficient on x86 machines because return instructions, too, can be speculatively executed. Kernel and hypervisor developers have developed mitigations in coordination with Intel and AMD. Mitigating Retbleed in the Linux kernel required a substantial effort, involving changes to 68 files, 1783 new lines and 387 removed lines. Our performance evaluation shows that mitigating Retbleed has unfortunately turned out to be expensive: we have measured between 14% and 39% overhead with the AMD and Intel patches respectively. Those mitigations were pulled into the mainline kernel today. They are not in the July 12 stable kernel updates but will almost certainly show up in those channels soon.
https://lwn.net/Articles/900917/
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