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[Bug 1775137] Re: Prevent speculation on user controlled pointer

To: group.of.nepali.translators@xxxxxxxxxxxxxxxxxxx
From: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Date: Wed, 06 Jun 2018 15:05:28 -0000
Reply-to: Bug 1775137 <1775137@xxxxxxxxxxxxxxxxxx>
Sender: bounces@xxxxxxxxxxxxx

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1775137

Title:
  Prevent speculation on user controlled pointer

Status in linux package in Ubuntu:
  Incomplete
Status in linux source package in Xenial:
  New

Bug description:
  == SRU Justification ==
  Upstream's Spectre v1 mitigation prevents speculation on a user controlled pointer. This part of the Spectre v1 patchset was never backported to 4.4 (for unknown reasons) so Xenial/Trusty/Precise are lacking it as well. All the other stable upstream kernels include it, so add it to our older kernels.

  == Fix ==
  Backport the following patches:
  x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec
  x86/usercopy: Replace open coded stac/clac with __uaccess_{begin, end}
  x86: Introduce __uaccess_begin_nospec() and uaccess_try_nospec

  == Regression Potential ==
  Low. Patches have been in upstream (and other distro kernels) for quite a while now and the changes only introduce a barrier on copy_from_user operations.

  == Test Case ==
  TBD.

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