[PATCH 3.16.y-ckt 050/170] KVM: x86: Improve thread safety in pit

From: Luis Henriques
Date: Tue Nov 11 2014 - 06:57:58 EST


3.16.7-ckt1 -stable review patch. If anyone has any objections, please let me know.

------------------

From: Andy Honig <ahonig@xxxxxxxxxx>

commit 2febc839133280d5a5e8e1179c94ea674489dae2 upstream.

There's a race condition in the PIT emulation code in KVM. In
__kvm_migrate_pit_timer the pit_timer object is accessed without
synchronization. If the race condition occurs at the wrong time this
can crash the host kernel.

This fixes CVE-2014-3611.

Signed-off-by: Andrew Honig <ahonig@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
arch/x86/kvm/i8254.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 518d86471b76..298781d4cfb4 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -262,8 +262,10 @@ void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu)
return;

timer = &pit->pit_state.timer;
+ mutex_lock(&pit->pit_state.lock);
if (hrtimer_cancel(timer))
hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
+ mutex_unlock(&pit->pit_state.lock);
}

static void destroy_pit_timer(struct kvm_pit *pit)
--
2.1.0

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