A proposed covert channel based on memory reclamation

This paper proposes a covert channel that is specific to virtual machine monitors (VMMs); it is called VMM memory reclamation-based covert storage channel. The paper describes a prospective information leakage attack that can be launched on security-critical processes running in a targeted virtual machine (VM) using the discovered covert channel. This attack exploits a widely adopted VM dynamic memory allocation mechanism called ballooning to breach inter-VM isolation. It involves two cooperating malicious processes: the sender process and the receiver process executing in two VMs: the target VM and the attacking VM respectively. Both VMs run concurrently on top of the same bare-metal VMM. Both malicious processes have access to the dynamically-allocated shared physical memory that is managed by the VMM, and multiplexed between both VMs. The malicious processes exploit the shared memory as a communication medium to leak confidential data. Through VMM memory reclamation-based covert storage channel, the sender process and the receiver process cooperate to force the VMM to reclaim memory pages from the target VM and allocate them to the attacking VM as extra memory space, thereby leaking information from the sender process to the receiver process.