Protecting users' privacy in virtualized cloud environments is an increasing concern for both users and providers. A hypervisor provides a hosting facility administrator with the capabilities to read the memory space of any guest VM. Therefore, nothing really prevents such an administrator from abusing these capabilities to access users' data. This threat is not prevented even if the whole memory is encrypted with a single (secret) key. Guest VM's can be isolated from the administrator if each guest VM has its memory space encrypted with a unique per-VM key. Here, while the hypervisor's memory access capabilities remain unchanged, reading a VM memory decrypts the VM's encrypted data with the wrong key and therefore gives no advantage to the attacker. This is indeed the motivation behind some newly proposed technologies that are planned in future processors.
However, this presentation argues that the privacy claim of any technology that uses different encryption keys to isolate hypervisor administrators from guest VM's cannot be guaranteed. To show this, we explain and demonstrate a new instantiation of a "Blinded Random Corruption Attack". Under the same scenario assumptions that the per-VM keying method addresses, our attack allows the cloud provider administrator to use the capabilities of a (trusted) hypervisor in order to login to a guest VM. This completely compromises the user's data privacy.
This shows, once again, that memory encryption by itself, is not necessarily a defense-in-depth mechanism against attackers with memory read/write capabilities. A better guarantee is achieved if the memory encryption includes some authentication mechanism.
Rodrigo Rubira Branco (BSDaemon) works as Principal Security Researcher at Intel Corporation in the Security Center of Excellence where he leads the Core Client, BIOS and IoT SoC Teams. Rodrigo released dozens of vulnerabilities in many important software in the past. In 2011 he was honored as one of the top contributors of Adobe. He is a member of the RISE Security Group and is the organizer of Hackers to Hackers Conference (H2HC), the oldest security research conference in Latin America. He is an active contributor to open-source projects (like ebizzy, linux kernel, others). Accepted speaker in lots of security and open-source related events as Black Hat, Hack in The Box, XCon, OLS, Defcon, Hackito, Zero Nights, Troopers and many others.