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x86/speculation: Prevent deadlock on ssb_state::lock

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commit 2f5fb19341883bb6e37da351bc3700489d8506a7 upstream.

Mikhail reported a lockdep splat related to the AMD specific ssb_state
lock:

  CPU0                       CPU1
  lock(&st->lock);
                             local_irq_disable();
                             lock(&(&sighand->siglock)->rlock);
                             lock(&st->lock);
  <Interrupt>
     lock(&(&sighand->siglock)->rlock);

  *** DEADLOCK ***

The connection between sighand->siglock and st->lock comes through seccomp,
which takes st->lock while holding sighand->siglock.

Make sure interrupts are disabled when __speculation_ctrl_update() is
invoked via prctl() -> speculation_ctrl_update(). Add a lockdep assert to
catch future offenders.

Fixes: 1f50ddb4f4 ("x86/speculation: Handle HT correctly on AMD")
Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Cc: Thomas Lendacky <thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1904141948200.4917@nanos.tec.linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Thomas Gleixner 2019-04-14 19:51:06 +02:00 committed by Greg Kroah-Hartman
parent 90e17512f1
commit 5680b0635c
1 changed files with 6 additions and 2 deletions
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8
arch/x86/kernel/process.c
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@ -411,6 +411,8 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp,
u64 msr = x86_spec_ctrl_base;
bool updmsr = false;
lockdep_assert_irqs_disabled();
/*
* If TIF_SSBD is different, select the proper mitigation
* method. Note that if SSBD mitigation is disabled or permanentely
@ -462,10 +464,12 @@ static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)
void speculation_ctrl_update(unsigned long tif)
{
unsigned long flags;
/* Forced update. Make sure all relevant TIF flags are different */
preempt_disable();
local_irq_save(flags);
__speculation_ctrl_update(~tif, tif);
preempt_enable();
local_irq_restore(flags);
}
/* Called from seccomp/prctl update */