The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2f5fb19341883bb6e37da351bc3700489d8506a7 Mon Sep 17 00:00:00 2001

From: Thomas Gleixner tglx@linutronix.de Date: Sun, 14 Apr 2019 19:51:06 +0200 Subject: [PATCH] x86/speculation: Prevent deadlock on ssb_state::lock

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: 1f50ddb4f418 ("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.linut...

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 58ac7be52c7a..957eae13b370 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -426,6 +426,8 @@ 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 @@ -477,10 +479,12 @@ 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 */