[PATCH 3.4 079/177] KVM: x86: Improve thread safety in pit

[lizf]

From: Andy Honig <ahonig@xxxxxxxxxx>

3.4.106-rc1 review patch.  If anyone has any objections, please let me know.

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


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>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>
---
 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 d68f99d..db336f9 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -263,8 +263,10 @@ void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu)
 		return;
 
 	timer = &pit->pit_state.pit_timer.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)
-- 
1.9.1

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