New speculative execution bug leaks data from Intel chips’ internal buffers

Intel-specific vulnerability was found by researchers both inside and outside the company.

First disclosed in January 2018, the Meltdown and Spectre attacks have opened the floodgates, leading to extensive research into the speculative execution hardware found in modern processors, and a number of additional attacks have been published in the months since.

Today sees the publication of a range of closely related flaws named variously RIDL, Fallout, ZombieLoad, or Microarchitectural Data Sampling. The many names are a consequence of the several groups that discovered the different flaws. From the computer science department of Vrije Universiteit Amsterdam and Helmholtz Center for Information Security, we have "Rogue In-Flight Data Load." From a team spanning Graz University of Technology, the University of Michigan, Worcester Polytechnic Institute, and KU Leuven, we have "Fallout." From Graz University of Technology, Worcester Polytechnic Institute, and KU Leuven, we have "ZombieLoad," and from Graz University of Technology, we have "Store-to-Leak Forwarding."

Intel is using the name "Microarchitectural Data Sampling" (MDS), and that's the name that arguably gives the most insight into the problem. The issues were independently discovered by both Intel and the various other groups, with the first notification to the chip company occurring in June last year.

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Google: Software is never going to be able to fix Spectre-type bugs

Researchers also devise a Spectre-like attack with no known mitigation.

Google: Software is never going to be able to fix Spectre-type bugs

Enlarge (credit: Aurich Lawson / Getty Images)

Researchers from Google investigating the scope and impact of the Spectre attack have published a paper asserting that Spectre-like vulnerabilities are likely to be a continued feature of processors and, further, that software-based techniques for protecting against them will both impose a high performance cost. In any case, the researchers continue, the software will be inadequate—some Spectre flaws don't appear to have any effective software-based defense. As such, Spectre is going to be a continued feature of the computing landscape, with no straightforward resolution.

The discovery and development of the Meltdown and Spectre attacks was undoubtedly the big security story of 2018. First revealed last January, new variants and related discoveries were made throughout the rest of the year. Both attacks rely on discrepancies between the theoretical architectural behavior of a processor—the documented behavior that programmers depend on and write their programs against—and the real behavior of implementations.

Specifically, modern processors all perform speculative execution; they make assumptions about, for example, a value being read from memory or whether an if condition is true or false, and they allow their execution to run ahead based on these assumptions. If the assumptions are correct, the speculated results are kept; if it isn't, the speculated results are discarded and the processor redoes the calculation. Speculative execution is not an architectural feature of the processor; it's a feature of implementations, and so it's supposed to be entirely invisible to running programs. When the processor discards the bad speculation, it should be as if the speculation never even happened.

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Researchers use Intel SGX to put malware beyond the reach of antivirus software

Processor protects malware from attempts to inspect and analyze it.

Intel Skylake die shot.

Intel Skylake die shot. (credit: Intel)

Researchers have found a way to run malicious code on systems with Intel processors in such a way that the malware can't be analyzed or identified by antivirus software, using the processor's own features to protect the bad code. As well as making malware in general harder to examine, bad actors could use this protection to, for example, write ransomware applications that never disclose their encryption keys in readable memory, making it substantially harder to recover from attacks.

The research, performed at Graz University of Technology by Michael Schwarz, Samuel Weiser, and Daniel Gruss (one of the researchers behind last year's Spectre attack), uses a feature that Intel introduced with its Skylake processors called SGX ("Software Guard eXtensions"). SGX enables programs to carve out enclaves where both the code and the data the code works with are protected to ensure their confidentiality (nothing else on the system can spy on them) and integrity (any tampering with the code or data can be detected). The contents of an enclave are transparently encrypted every time they're written to RAM and decrypted upon being read. The processor governs access to the enclave memory: any attempt to access the enclave's memory from code outside the enclave is blocked; the decryption and encryption only occurs for the code within the enclave.

SGX has been promoted as a solution to a range of security concerns when a developer wants to protect code, data, or both, from prying eyes. For example, an SGX enclave running on a cloud platform could be used to run custom proprietary algorithms, such that even the cloud provider cannot determine what the algorithms are doing. On a client computer, the SGX enclave could be used in a similar way to enforce DRM (digital rights management) restrictions; the decryption process and decryption keys that the DRM used could be held within the enclave, making them unreadable to the rest of the system. There are biometric products on the market that use SGX enclaves for processing the biometric data and securely storing it such that it can't be tampered with.

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Spectre, Meltdown researchers unveil 7 more speculative execution attacks

Systemic analysis reveals a range of new issues and a need for new mitigations.

Spectre, Meltdown researchers unveil 7 more speculative execution attacks

Enlarge (credit: Aurich Lawson / Getty Images)

Back at the start of the year, a set of attacks that leveraged the speculative execution capabilities of modern high-performance processors was revealed. The attacks were named Meltdown and Spectre. Since then, numerous variants of these attacks have been devised. In tandem, a range of mitigation techniques has been created to enable at-risk software, operating systems, and hypervisor platforms to protect against these attacks.

A research team—including many of the original researchers behind Meltdown, Spectre, and the related Foreshadow and BranchScope attacks—has published a new paper disclosing yet more attacks in the Spectre and Meltdown families. The result? Seven new possible attacks. Some are mitigated by known mitigation techniques, but others are not. That means further work is required to safeguard vulnerable systems.

The previous investigations into these attacks has been a little ad hoc in nature; examining particular features of interest to provide, for example, a Spectre attack that can be performed remotely over a network, or Meltdown-esque attack to break into SGX enclaves. The new research is more systematic, looking at the underlying mechanisms behind both Meltdown and Spectre and running through all the different ways the speculative execution can be misdirected.

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