• Software protects data • All software is (eventually) hackable • Finding/fixing vulnerabilities doesn’t scale • E.g., Malicious 7: buffer errors, code injection, numeric errors, permissions, resource mgt

There is an increasing body of work in the area of hardware defenses for software-driven security attacks. A significant challenge in developing these defenses is that the space of security vulnerabilities and exploits is large and not fully understood. This results in specific point defenses that aim to patch particular vulnerabilities. While these defenses are valuable, they are often blindsided by fresh attacks that exploit new vulnerabilities. This article aims to address this issue by suggesting ways to make future defenses more durable based on an organization of security vulnerabilities as they arise throughout the program life cycle. We classify these vulnerability sources through programming, compilation, and hardware realization, and we show how each source introduces unintended states and transitions into the implementation. Further, we show how security exploits gain control by moving the implementation to an unintended state using knowledge of these sources and how defenses work to prevent these transitions. This framework of analyzing vulnerability sources, exploits, and defenses provides insights into developing durable defenses that could defend against broader categories of exploits. We present illustrative case studies of four important attack genealogies—showing how they fit into the presented framework and how the sophistication of the exploits and defenses have evolved over time, providing us insights for the future.

Attacks often succeed by abusing the gap between program and machine-level semantics-- for example, by locating a sensitive pointer, exploiting a bug to overwrite this sensitive data, and hijacking the victim program's execution. In this work, we take secure system design on the offensive by continuously obfuscating information that attackers need but normal programs do not use, such as representation of code and pointers or the exact location of code and data. Our secure hardware architecture, Morpheus, combines two powerful protections: ensembles of moving target defenses and churn. Ensembles of moving target defenses randomize key program values (e.g., relocating pointers and encrypting code and pointers) which forces attackers to extensively probe the system prior to an attack. To ensure attack probes fail, the architecture incorporates churn to transparently re-randomize program values underneath the running system. With frequent churn, systems quickly become impractically difficult to penetrate. We demonstrate Morpheus through a RISC-V-based prototype designed to stop control-flow attacks. Each moving target defense in Morpheus uses hardware support to individually offer more randomness at a lower cost than previous techniques. When ensembled with churn, Morpheus defenses offer strong protection against control-flow attacks, with our security testing and performance studies revealing: i) high-coverage protection for a broad array of control-flow attacks, including protections for advanced attacks and an attack disclosed after the design of Morpheus, and ii) negligible performance impacts (1%) with churn periods up to 50 ms, which our study estimates to be at least 5000x faster than the time necessary to possibly penetrate Morpheus.

Memory corruption vulnerabilities in type-unsafe languages are often exploited to perform a control-flow hijacking attack, in which an attacker uses vulnerabilities to corrupt control data in the program to eventually gain control over the execution of the program. However, widespread adoption of control-flow attack defenses such as Control-flow Integrity (CFI) has led attackers to exploit memory errors to corrupt non-control data that can not be detected by these defenses. Non-control data attacks can be used to corrupt security critical data or leak sensitive information. Moreover, recent attacks such as data-oriented programming (DOP) have generalized non-control data attacks to achieve Turing-complete computation capabilities within the programmer-specified control-flow graph, leaving previously proposed control-flow protections unable to stop these attacks.In this paper, we present a stack-layout randomization scheme that can effectively thwart DOP attacks. Our approach, called Smokestack, provides each function invocation with a randomly permuted ordering of the local stack organization. In addition, we utilize true-random value sources combined with disclosure-resistant pseudo-random number generation to ensure that an adversary cannot anticipate a function-s invocation permutation of automatic variables. Our evaluation on SPEC benchmarks and various real-world applications shows that Smokestack can stop DOP attacks with minimal overhead.

Previous work has demonstrated that systems with unencrypted DRAM interfaces are susceptible to cold boot attacks - where the DRAM in a system is frozen to give it sufficient retention time and is then re-read after reboot, or is transferred to an attacker's machine for extracting sensitive data. This method has been shown to be an effective attack vector for extracting disk encryption keys out of locked devices. However, most modern systems incorporate some form of data scrambling into their DRAM interfaces making cold boot attacks challenging. While first added as a measure to improve signal integrity and reduce power supply noise, these scramblers today serve the added purpose of obscuring the DRAM contents. It has previously been shown that scrambled DDR3 systems do not provide meaningful protection against cold boot attacks. In this paper, we investigate the enhancements that have been introduced in DDR4 memory scramblers in the 6thgeneration Intel Core (Skylake) processors. We then present an attack that demonstrates these enhanced DDR4 scramblers still do not provide sufficient protection against cold boot attacks. We detail a proof-of-concept attack that extracts memory resident AES keys, including disk encryption keys. The limitations of memory scramblers we point out in this paper motivate the need for strong yet low-overhead fullmemory encryption schemes. Existing schemes such as Intel's SGX can effectively prevent such attacks, but have overheads that may not be acceptable for performance-sensitive applications. However, it is possible to deploy a memory encryption scheme that has zero performance overhead by forgoing integrity checking and replay attack protections afforded by Intel SGX. To that end, we present analyses that confirm modern stream ciphers such as ChaCha8 are sufficiently fast that it is now possible to completely overlap keystream generation with DRAM row buffer access latency, thereby enabling the creation of strongly encrypted DRAMs with zero exposed latency. Adopting such low-overhead measures in future generation of products can effectively shut down cold boot attacks in systems where the overhead of existing memory encryption schemes is unacceptable. Furthermore, the emergence of non-volatile DIMMs that fit into DDR4 buses is going to exacerbate the risk of cold boot attacks. Hence, strong full memory encryption is going to be even more crucial on such systems.