Throwhammer: Rowhammer attacks over the network and defenses

Increasingly sophisticated Rowhammer exploits allow an attacker that can execute code on a vulnerable system to escalate privileges and compromise browsers, clouds, and mobile systems. In all these attacks, the common assumption is that attackers first need to obtain code execution on the victim machine to be able to exploit Rowhammer either by having (unprivileged) code execution on the victim machine or by luring the victim to a website that employs a malicious JavaScript application. In this paper, we revisit this assumption and show that an attacker can trigger and exploit Rowhammer bit flips directly from a remote machine by only sending network packets. This is made possible by increasingly fast, RDMA-enabled networks, which are in wide use in clouds and data centers. To demonstrate the new threat, we show how a malicious client can exploit Rowhammer bit flips to gain code execution on a remote key-value server application. To counter this threat, we propose protecting unmodified applications with a new buffer allocator that is capable of fine-grained memory isolation in the DRAM address space. Using two real-world applications, we show that this defense is practical, self-contained, and can efficiently stop remote Rowhammer attacks by surgically isolating memory buffers that are exposed to untrusted network input.