KVM: Fix bounds checking in ioapic indirect register reads (CVE-2013-1798)

If the guest specifies a IOAPIC_REG_SELECT with an invalid value and follows
that with a read of the IOAPIC_REG_WINDOW KVM does not properly validate
that request.  ioapic_read_indirect contains an
ASSERT(redir_index < IOAPIC_NUM_PINS), but the ASSERT has no effect in
non-debug builds.  In recent kernels this allows a guest to cause a kernel
oops by reading invalid memory.  In older kernels (pre-3.3) this allows a
guest to read from large ranges of host memory.

Tested: tested against apic unit tests.

Signed-off-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
int kvm_get_ioapic(struct kvm *kvm, struct kvm_ioapic_state *state)
{
	struct kvm_ioapic *ioapic = ioapic_irqchip(kvm);
	if (!ioapic)
		return -EINVAL;

	spin_lock(&ioapic->lock);
	memcpy(state, ioapic, sizeof(struct kvm_ioapic_state));
	spin_unlock(&ioapic->lock);
	return 0;
}

int kvm_get_ioapic(struct kvm *kvm, struct kvm_ioapic_state *state)
{
	struct kvm_ioapic *ioapic = ioapic_irqchip(kvm);
	if (!ioapic)
		return -EINVAL;

	spin_lock(&ioapic->lock);
	memcpy(state, ioapic, sizeof(struct kvm_ioapic_state));
	spin_unlock(&ioapic->lock);
	return 0;
}
