static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val)
{
	unsigned index;
	bool mask_before, mask_after;
	union kvm_ioapic_redirect_entry *e;

	switch (ioapic->ioregsel) {
	case IOAPIC_REG_VERSION:
		/* Writes are ignored. */
		break;

	case IOAPIC_REG_APIC_ID:
		ioapic->id = (val >> 24) & 0xf;
		break;

	case IOAPIC_REG_ARB_ID:
		break;

	default:
		index = (ioapic->ioregsel - 0x10) >> 1;

		ioapic_debug("change redir index %x val %x\n", index, val);
		if (index >= IOAPIC_NUM_PINS)
			return;
		e = &ioapic->redirtbl[index];
		mask_before = e->fields.mask;
		if (ioapic->ioregsel & 1) {
			e->bits &= 0xffffffff;
			e->bits |= (u64) val << 32;
		} else {
			e->bits &= ~0xffffffffULL;
			e->bits |= (u32) val;
			e->fields.remote_irr = 0;
		}
		mask_after = e->fields.mask;
		if (mask_before != mask_after)
			kvm_fire_mask_notifiers(ioapic->kvm, KVM_IRQCHIP_IOAPIC, index, mask_after);
		if (e->fields.trig_mode == IOAPIC_LEVEL_TRIG
		    && ioapic->irr & (1 << index))
			ioapic_service(ioapic, index, false);
		kvm_vcpu_request_scan_ioapic(ioapic->kvm);
		break;
	}
}

The product reads data past the end, or before the beginning, of the intended buffer.