queue-4.14/x86-speculation-prevent-deadlock-on-ssb_state-lock.patch

   1 From 2f5fb19341883bb6e37da351bc3700489d8506a7 Mon Sep 17 00:00:00 2001
   2 From: Thomas Gleixner <tglx@linutronix.de>
   3 Date: Sun, 14 Apr 2019 19:51:06 +0200
   4 Subject: x86/speculation: Prevent deadlock on ssb_state::lock
   5
   6 From: Thomas Gleixner <tglx@linutronix.de>
   7
   8 commit 2f5fb19341883bb6e37da351bc3700489d8506a7 upstream.
   9
  10 Mikhail reported a lockdep splat related to the AMD specific ssb_state
  11 lock:
  12
  13   CPU0                       CPU1
  14   lock(&st->lock);
  15                              local_irq_disable();
  16                              lock(&(&sighand->siglock)->rlock);
  17                              lock(&st->lock);
  18   <Interrupt>
  19      lock(&(&sighand->siglock)->rlock);
  20
  21   *** DEADLOCK ***
  22
  23 The connection between sighand->siglock and st->lock comes through seccomp,
  24 which takes st->lock while holding sighand->siglock.
  25
  26 Make sure interrupts are disabled when __speculation_ctrl_update() is
  27 invoked via prctl() -> speculation_ctrl_update(). Add a lockdep assert to
  28 catch future offenders.
  29
  30 Fixes: 1f50ddb4f418 ("x86/speculation: Handle HT correctly on AMD")
  31 Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
  32 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  33 Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
  34 Cc: Thomas Lendacky <thomas.lendacky@amd.com>
  35 Cc: stable@vger.kernel.org
  36 Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1904141948200.4917@nanos.tec.linutronix.de
  37 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  38
  39 ---
  40  arch/x86/kernel/process.c |    8 ++++++--
  41  1 file changed, 6 insertions(+), 2 deletions(-)
  42
  43 --- a/arch/x86/kernel/process.c
  44 +++ b/arch/x86/kernel/process.c
  45 @@ -465,10 +467,12 @@ static unsigned long speculation_ctrl_up
  46
  47  void speculation_ctrl_update(unsigned long tif)
  48  {
  49 +       unsigned long flags;
  50 +
  51         /* Forced update. Make sure all relevant TIF flags are different */
  52 -       preempt_disable();
  53 +       local_irq_save(flags);
  54         __speculation_ctrl_update(~tif, tif);
  55 -       preempt_enable();
  56 +       local_irq_restore(flags);
  57  }
  58
  59  /* Called from seccomp/prctl update */