Intel Falls Prey to Lord of the Rings Side-Channel Attack

Security researchers this month disclosed a novel side-channel attack affecting Intel Skylake and Coffee Lake series processors. Security researchers this month disclosed a novel side-channel attack affecting Intel Skylake and Coffee Lake series processors. In a report titled “Lord of the Ring(s),” researchers claimed to have demonstrated the first side-channel attack targeting the ring interconnect used in many current-generation Intel CPUs to obtain sensitive information such as passwords and RSA keys. In a statement, Intel confirmed the vulnerability and thanked the researchers for their work. “After reviewing the paper, we believe developers and system administrators can employ a number of security best practices that help protect against various types of side-channel attacks, including those found in this paper,” a spokesperson wrote in an email to SDxCentral. For those that aren’t familiar, side-channel attacks take advantage of electromagnetic radiation coming off electronic devices during normal operation to identify patterns and glean useful information. However, unlike the high-profile Spectre and Meltdown attacks, the attack disclosed this week doesn’t rely on previous exploits. It is also immune to countermeasures enacted by chipmakers in the wake of those attacks, the researchers claimed. The exploit takes advantage of how each of the components within Intel CPUs communicate with each other. This fabric, often called a ring interconnect or ring bus, was introduced with the launch of Intel’s Nehalem-EX microarchitecture in 2008 and is still widely used by Intel today, the report states. Researchers started by reverse engineering the ring bus using two machines. The first machine used a 9th-generation Core i7 processor based on the Coffee Lake architecture, and the second using a sixth-generation Core i7 Skylake processor. Both chips have known vulnerabilities to previously disclosed side-channel attacks. While the experiments used consumer hardware, researchers note that, apart from a handful of recent server chips from Intel, the ring bus appears to be vulnerable to exploit. Using these machines, the researchers developed a monitoring program that took measurements from each core. This information was loaded into a machine-learning algorithm to filter out noise from useful information. Using these tools they were able to execute two side-channel attacks using the ring bus exploit. The first attack took advantage of mitigations to preemptive scheduling cache attacks — another variety of side-channel attack — to cause the “victim’s loads to miss in the cache.” This, researchers claim, allowed them to leak RSA key information by monitoring the ring bus. The second attack targeted keystroke timing information. Researchers claim that when a user pressed a key, it caused a spike in contention on the ring bus, which can be used to infer authentication data such as usernames and passwords. According to the report, the first attack is somewhat limited in its scope as it relies on the victim’s cache being cleansed on context switches — a security measure that is not implemented in most major operating systems. However, while not commonly implemented, it is recommended to mitigate other forms of side-channel attacks. This creates what the researchers called a “lose-lose scenario,” in which users are at risk of preemptive scheduling attacks if cache cleansing is turned off and ring bus attacks if it’s enabled. According to the report, Intel, which has been notified of the exploit, has classified it as a “traditional side-channel” attack, because it takes advantage of the chip’s architecture. While the research was limited to Intel’s ring bus architecture, researchers note that it should be possible to port the attack to other CPUs using similar interconnect technologies. “We were able to replicate our methodology on a server-class Xeon Broadwell CPU, finding that the distributed boxcar-based arbitration policy is the same that we observed on our client-class CPUs,” the researchers wrote. They add that it remains unclear whether the attack can be used to target chips not using a ring interconnect, like Intel’s more recent server processors. The authors are also investigating whether the attack could be modified to compromise systems using AMD’s EPYC series chips.