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While running an Ubuntu kernel (not a mainline or third-party kernel)
please enter the following command in a terminal window:

apport-collect 1967579

and then change the status of the bug to 'Confirmed'.

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This change has been made by an automated script, maintained by the
Ubuntu Kernel Team.

** Changed in: linux (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1967579

Title:
  harden indirect calls against BHI attacks

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  [Impact]
  Branch History Injection is made easier when all indirect calls are funneled 
through very few points where the retpolines were. By replacing the retpoline 
jumps by indirect calls whenever retpolines are disabled, BHI attacks are more 
difficult to execute as the BTB is not as fixed as before.

  [Fixes]
  Though there are fixes that allow retpoline,lfence to be directly replaced in 
the indirect calls, given that mitigation is not recommended for most of the 
situations, that hardening is not as important as the one that works for the 
spectre_v2=off option (the default one for systems with eIBRS). This latter one 
is present starting with 5.13, but backporting to 5.4 might be a good measure.

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