Verified the issue to be fixed with Trusty kernel 3.13.0-145.194.

** Tags removed: verification-needed-trusty
** Tags added: verification-done-trusty

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  Segmentation fault in ldt_gdt_64

Status in linux package in Ubuntu:
Status in linux source package in Trusty:
  Fix Committed

Bug description:
  == SRU Justification ==
  The ldt_gdt_64 x86 selftest segfaults with the currently released Trusty 3.13 
kernel. The commit that introduced the segfault is aeb315d60afe ("x86/ldt: Make 
modify_ldt synchronous").

  == Fix ==
  Upstream commit 8ff5bd2e1e27 ("x86/signal/64: Fix SS if needed when 
delivering a 64-bit signal"). This commit was found by doing a reverse git 
bisect of the upstream kernel (i.e., when did the test stop segfaulting).
  The backport of the commit is a simple context adjustment. The second commit 
is a pre-requisite which simply renames some defines (no functional changes).

  == Regression Potential ==
  Low. The commit is very small and isolated and the code path is only executed 
in special circumstances (and for x86 only). I built a test kernel and ran the 
whole set of x86 selftests and perf NMI test for several hours to verify 

  == Test Case ==
  Run the ldt_gdt_64 x86 selftets from a current upstream kernel source. The 
test segfaults consistently.

  Original bug description:

  Trusty 3.13 segfaults when running ldt_gdt_64 from the kernel's x86

  git bisect revealed that the following commit introduced the issue:

  commit aeb315d60afee129d32558f4a4b356eec2e7da7b
  Author: Andy Lutomirski <>
  Date:   Thu Jul 30 14:31:32 2015 -0700

      x86/ldt: Make modify_ldt synchronous


      commit 37868fe113ff2ba814b3b4eb12df214df555f8dc upstream.

      modify_ldt() has questionable locking and does not synchronize
      threads.  Improve it: redesign the locking and synchronize all
      threads' LDTs using an IPI on all modifications.

      This will dramatically slow down modify_ldt in multithreaded
      programs, but there shouldn't be any multithreaded programs that
      care about modify_ldt's performance in the first place.

      This fixes some fallout from the CVE-2015-5157 fixes.

      Signed-off-by: Andy Lutomirski <>
      Reviewed-by: Borislav Petkov <>
      Cc: Andrew Cooper <>
      Cc: Andy Lutomirski <>
      Cc: Boris Ostrovsky <>
      Cc: Borislav Petkov <>
      Cc: Brian Gerst <>
      Cc: Denys Vlasenko <>
      Cc: H. Peter Anvin <>
      Cc: Jan Beulich <>
      Cc: Konrad Rzeszutek Wilk <>
      Cc: Linus Torvalds <>
      Cc: Peter Zijlstra <>
      Cc: Sasha Levin <>
      Cc: Steven Rostedt <>
      Cc: Thomas Gleixner <>
      Signed-off-by: Ingo Molnar <>
      Signed-off-by: Jiri Slaby <>
      (cherry picked from commit 62fc7228f8cc8c89ecbd37008a0495ac28e41c5c)
      Signed-off-by: Juerg Haefliger <>
      Signed-off-by: Stefan Bader <>

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