Biblio

Shielding systems such as AMD's Secure Encrypted Virtualization aim to protect a virtual machine from a higher privileged entity such as the hypervisor. A cornerstone of these systems is the ability to protect the memory from unauthorized accesses. Despite this protection mechanism, previous attacks leveraged the control over memory resources to infer control flow of applications running in a shielded system. While previous works focused on a specific target application, there has been no general analysis on how the control flow of a protected application can be inferred. This paper tries to overcome this gap by providing a detailed analysis on the detectability of control flow using memory access patterns. To that end, we do not focus on a specific shielding system or a specific target application, but present a framework which can be applied to different types of shielding systems as well as to different types of attackers. By training a random forest classifier on the memory accesses emitted by syscalls of a shielded entity, we show that it is possible to infer the control flow of shielded entities with a high degree of accuracy.

Adversaries with physical access to a target platform can perform cold boot or DMA attacks to extract sensitive data from the RAM. To prevent such attacks, hardware vendors announced respective processor extensions. AMD's extension SME will provide means to encrypt the RAM to protect security-relevant assets that reside there. The encryption will protect the user's content against passive eavesdropping. However, the level of protection it provides in scenarios that involve an adversary who cannot only read from RAM but also change content in RAM is less clear. This paper addresses the open research question whether encryption alone is a dependable protection mechanism in practice when considering an active adversary. To this end, we first build a software based memory encryption solution on a desktop system which mimics AMD's SME. Subsequently, we demonstrate a proof-of-concept fault attack on this system, by which we are able to extract the private RSA key of a GnuPG user. Our work suggests that transparent memory encryption is not enough to prevent active attacks.