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  1. Aug 19, 2022
    • Daniel Sneddon's avatar
      x86/speculation: Add RSB VM Exit protections · 42268ea1
      Daniel Sneddon authored
      stable inclusion
      from stable-v4.19.255
      commit b6c5011934a15762cd694e36fe74f2f2f93eac9b
      category: bugfix
      bugzilla: 187492, https://gitee.com/src-openeuler/kernel/issues/I5N1SO
      CVE: CVE-2022-26373
      
      --------------------------------
      
      commit 2b1299322016731d56807aa49254a5ea3080b6b3 upstream.
      
      tl;dr: The Enhanced IBRS mitigation for Spectre v2 does not work as
      documented for RET instructions after VM exits. Mitigate it with a new
      one-entry RSB stuffing mechanism and a new LFENCE.
      
      == Background ==
      
      Indirect Branch Restricted Speculation (IBRS) was designed to help
      mitigate Branch Target Injection and Speculative Store Bypass, i.e.
      Spectre, attacks. IBRS prevents software run in less privileged modes
      from affecting branch prediction in more privileged modes. IBRS requires
      the MSR to be written on every privilege level change.
      
      To overcome some of the performance issues of IBRS, Enhanced IBRS was
      introduced.  eIBRS is an "always on" IBRS, in other words, just turn
      it o...
      42268ea1
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