Commit b33ac88b authored Oct 21, 2007 by Kevin Pedretti Committed by Avi Kivity Oct 22, 2007

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: Kevin Pedretti <kevin.pedretti@gmail.com>
Signed-off-by: Avi 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;

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