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Intel CPUs Fall to New Hyperthreading Exploit That Pilfers Crypto Keys


Intel's Core i7 central processing unit.

Researchers have found yet another leak on a wide range of Intel chips that may also affect chips made by other manufacturers.

Credit: Intel

Over the past 11 months, the processors running our computers, and in some cases phones, have succumbed to a host of attacks. Bearing names such as Meltdown and Spectre, BranchScope, TLBleed, and Foreshadow, the exploits threaten to siphon some of our most sensitive secrets—say passwords or cryptographic keys—out of the silicon microarchitecture in ways that can't be detected or stopped by traditional security defenses. On Friday, researchers disclosed yet another leak that has already been shown to exist on a wide range of Intel chips and may also affect other makers, too.

PortSmash, as the new attack is being called, exploits a largely overlooked side-channel in Intel's hyperthreading technology. A proprietary implementation of simultaneous multithreading, hyperthreading reduces the amount of time needed to carry out parallel computing tasks, in which large numbers of calculations or executions are carried out simultaneously. The performance boost is the result of two logical processor cores sharing the hardware of a single physical processor. The added logical cores make it easier to divide large tasks into smaller ones that can be completed more quickly.

Port contention as a side channel

In a paper scheduled for release soon, researchers document how they were able to exploit the newly discovered leak to recover an elliptic curve private key from a server running an OpenSSL-powered TLS server. The attack, which was carried out on servers running Intel Skylake and Kaby Lake chips and Ubuntu, worked by sending one logical core a steady stream of instructions and carefully measuring the time it took for them to get executed.

The specific timing allowed PortSmash to deduce the key being processed in another logical core of the same processor. The resource providing the leak is port contention, a phenomenon that happens when multiple instructions using the same physical processor resources get assigned to various ports to await completion. The vulnerability is indexed as CVE-2018-5407. It affects PCs as well as servers, although the vector for exploit generally favors the latter.

 

From Ars Technica
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