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Commit b33ac88b authored by Kevin Pedretti's avatar Kevin Pedretti Committed by Avi Kivity
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KVM: Fix local apic timer divide by zero 



kvm_lapic_reset() was initializing apic->timer.divide_count to 0,
which could potentially lead to a divide by zero error in
apic_get_tmcct().  Any guest that reads the APIC's CCR (current count)
register before setting DCR (divide configuration) would trigger a divide
by zero exception in the host kernel, leading to a host-OS crash.

This patch results in apic->timer.divide_count being initialized to
2 at reset, eliminating the bug (DCR=0 at reset, meaning divide by 2).

Signed-off-by: default avatarKevin Pedretti <kevin.pedretti@gmail.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 0552f73b

drivers/kvm/lapic.c

+1 −1
Original line number Diff line number Diff line
@@ -853,7 +853,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu) 
		apic_set_reg(apic, APIC_ISR + 0x10 * i, 0);

		apic_set_reg(apic, APIC_TMR + 0x10 * i, 0);

	}

	apic->timer.divide_count = 0;

	update_divide_count(apic);

	atomic_set(&apic->timer.pending, 0);

	if (vcpu->vcpu_id == 0)

		vcpu->apic_base |= MSR_IA32_APICBASE_BSP;