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KVM: x86/xen: Stop Xen timer before changing IRQ

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Stop Xen timer (if it's running) prior to changing the IRQ vector and
potentially (re)starting the timer. Changing the IRQ vector while the
timer is still running can result in KVM injecting a garbage event, e.g.
vm_xen_inject_timer_irqs() could see a non-zero xen.timer_pending from
a previous timer but inject the new xen.timer_virq.

Fixes: 5363952605 ("KVM: x86/xen: handle PV timers oneshot mode")
Cc: stable@vger.kernel.org
Link: https://syzkaller.appspot.com/bug?id=8234a9dfd3aafbf092cc5a7cd9842e3ebc45fc42
Reported-by: syzbot+e54f930ed78eb0f85281@syzkaller.appspotmail.com
Signed-off-by: Coleman Dietsch <dietschc@csp.edu>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20220808190607.323899-3-dietschc@csp.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Coleman Dietsch 2022-08-08 14:06:07 -05:00 committed by Paolo Bonzini
parent af735db312
commit c036899136
1 changed files with 17 additions and 18 deletions
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35
arch/x86/kvm/xen.c
View file

@ -707,26 +707,25 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
break;
case KVM_XEN_VCPU_ATTR_TYPE_TIMER:
if (data->u.timer.port) {
if (data->u.timer.priority != KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL) {
r = -EINVAL;
break;
}
vcpu->arch.xen.timer_virq = data->u.timer.port;
if (!vcpu->arch.xen.timer.function)
kvm_xen_init_timer(vcpu);
/* Restart the timer if it's set */
if (data->u.timer.expires_ns)
kvm_xen_start_timer(vcpu, data->u.timer.expires_ns,
data->u.timer.expires_ns -
get_kvmclock_ns(vcpu->kvm));
} else if (kvm_xen_timer_enabled(vcpu)) {
kvm_xen_stop_timer(vcpu);
vcpu->arch.xen.timer_virq = 0;
if (data->u.timer.port &&
data->u.timer.priority != KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL) {
r = -EINVAL;
break;
}
if (!vcpu->arch.xen.timer.function)
kvm_xen_init_timer(vcpu);
/* Stop the timer (if it's running) before changing the vector */
kvm_xen_stop_timer(vcpu);
vcpu->arch.xen.timer_virq = data->u.timer.port;
/* Start the timer if the new value has a valid vector+expiry. */
if (data->u.timer.port && data->u.timer.expires_ns)
kvm_xen_start_timer(vcpu, data->u.timer.expires_ns,
data->u.timer.expires_ns -
get_kvmclock_ns(vcpu->kvm));
r = 0;
break;