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Message-ID: <lsq.1565469607.972476944@decadent.org.uk>
Date: Sat, 10 Aug 2019 21:40:07 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
"Thomas Lendacky" <thomas.lendacky@....com>,
"Thomas Gleixner" <tglx@...utronix.de>,
"Mikhail Gavrilov" <mikhail.v.gavrilov@...il.com>
Subject: [PATCH 3.16 084/157] x86/speculation: Prevent deadlock on
ssb_state::lock
3.16.72-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Gleixner <tglx@...utronix.de>
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: 1f50ddb4f418 ("x86/speculation: Handle HT correctly on AMD")
Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
Cc: Thomas Lendacky <thomas.lendacky@....com>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1904141948200.4917@nanos.tec.linutronix.de
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
arch/x86/kernel/process.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -351,6 +351,8 @@ static __always_inline void __speculatio
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
@@ -402,10 +404,12 @@ static unsigned long speculation_ctrl_up
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 */
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