The University of SydneyPage 4Recap of Week 4 –Issues in Bell-La PadulaModel–Example: timing covert channel–The KVM/370 operating system isolated processes on separate virtual machines. They shared the processor on a time-sliced basis. Processes alternated using the CPU, with each allowed t units of processing time. However, a process could relinquish the CPU early. –If the sending virtual machine wished to send a “0” bit, it would relinquish the CPU immediately; to send a “1,” it would use its full quantum. By determining how quickly it got the CPU, the second virtual machine could deduce whether the first was sending a “1” or a “0.” –The shared resource is the CPU. –The processes communicate by using a real-time clock to measure the intervals between accesses to the shared resource