Intel Finds Bug In AMD's Spectre Mitigation, AMD Issues Fix

"News of a fresh Spectre BHB vulnerability that only impacts Intel and Arm processors emerged this week," reports Tom's Hardware, "but Intel's research around these new attack vectors unearthed another issue. "One of the patches that AMD has used to fix the Spectre vulnerabilities has been broken since 2018."Intel's security team, STORM, found the issue with AMD's mitigation. In response, AMD has issued a security bulletin and updated its guidance to recommend using an alternative method to mitigate the Spectre vulnerabilities, thus repairing the issue anew.... Intel's research into AMD's Spectre fix begins in a roundabout way - Intel's processors were recently found to still be susceptible to Spectre v2-based attacks via a new Branch History Injection variant, this despite the company's use of the Enhanced Indirect Branch Restricted Speculation (eIBRS) and/or Retpoline mitigations that were thought to prevent further attacks. In need of a newer Spectre mitigation approach to patch the far-flung issue, Intel turned to studying alternative mitigation techniques. There are several other options, but all entail varying levels of performance tradeoffs. Intel says its ecosystem partners asked the company to consider using AMD's LFENCE/JMP technique. The "LFENCE/JMP" mitigation is a Retpoline alternative commonly referred to as "AMD's Retpoline." As a result of Intel's investigation, the company discovered that the mitigation AMD has used since 2018 to patch the Spectre vulnerabilities isn't sufficient - the chips are still vulnerable. The issue impacts nearly every modern AMD processor spanning almost the entire Ryzen family for desktop PCs and laptops (second-gen to current-gen) and the EPYC family of datacenter chips.... In response to the STORM team's discovery and paper, AMD issued a security bulletin (AMD-SB-1026) that states it isn't aware of any currently active exploits using the method described in the paper. AMD also instructs its customers to switch to using "one of the other published mitigations (V2-1 aka 'generic retpoline' or V2-4 aka 'IBRS')." The company also published updated Spectre mitigation guidance reflecting those changes [PDF].... AMD's security bulletin thanks Intel's STORM team by name and noted it engaged in the coordinated vulnerability disclosure, thus allowing AMD enough time to address the issue before making it known to the public. Thanks to Slashdot reader Hmmmmmm for submitting the story...

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