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>
static int ioapic_deliver(struct kvm_ioapic *ioapic, int irq)
{
	union kvm_ioapic_redirect_entry *entry = &ioapic->redirtbl[irq];
	struct kvm_lapic_irq irqe;

	ioapic_debug("dest=%x dest_mode=%x delivery_mode=%x "
		     "vector=%x trig_mode=%x\n",
		     entry->fields.dest_id, entry->fields.dest_mode,
		     entry->fields.delivery_mode, entry->fields.vector,
		     entry->fields.trig_mode);

	irqe.dest_id = entry->fields.dest_id;
	irqe.vector = entry->fields.vector;
	irqe.dest_mode = entry->fields.dest_mode;
	irqe.trig_mode = entry->fields.trig_mode;
	irqe.delivery_mode = entry->fields.delivery_mode << 8;
	irqe.level = 1;
	irqe.shorthand = 0;

	return kvm_irq_delivery_to_apic(ioapic->kvm, NULL, &irqe);
}

static int ioapic_deliver(struct kvm_ioapic *ioapic, int irq)
{
	union kvm_ioapic_redirect_entry *entry = &ioapic->redirtbl[irq];
	struct kvm_lapic_irq irqe;

	ioapic_debug("dest=%x dest_mode=%x delivery_mode=%x "
		     "vector=%x trig_mode=%x\n",
		     entry->fields.dest_id, entry->fields.dest_mode,
		     entry->fields.delivery_mode, entry->fields.vector,
		     entry->fields.trig_mode);

	irqe.dest_id = entry->fields.dest_id;
	irqe.vector = entry->fields.vector;
	irqe.dest_mode = entry->fields.dest_mode;
	irqe.trig_mode = entry->fields.trig_mode;
	irqe.delivery_mode = entry->fields.delivery_mode << 8;
	irqe.level = 1;
	irqe.shorthand = 0;

	return kvm_irq_delivery_to_apic(ioapic->kvm, NULL, &irqe);
}
