The world has seen the most unsettling attack yet resulting from the so-called Rowhammer exploit, which flips individual bits in computer memory. It's a technique that's so surgical and controlled that it allows one machine to effectively steal the cryptographic keys of another machine hosted in the same cloud environment.

Until now, Rowhammer has been a somewhat clumsy and unpredictable attack tool because it was hard to control exactly where data-corrupting bit flips happened. While previous research demonstrated that it could be used to elevate user privileges and break security sandboxes, most people studying Rowhammer said there was little immediate danger of it being exploited maliciously to hijack the security of computers that use vulnerable chips. The odds of crucial data being stored in a susceptible memory location made such hacks largely a matter of chance that was stacked against the attacker. In effect, Rowhammer was more a glitch than an exploit.

Now, computer scientists have developed a significantly more refined Rowhammer technique they call Flip Feng Shui. It manipulates deduplication operations that many cloud hosts use to save memory resources by sharing identical chunks of data used by two or more virtual machines. Just as traditional Feng Shui aims to create alignment or harmony in a home or office, Flip Feng Shui can massage physical memory in a way that causes crypto keys and other sensitive data to be stored in locations known to be susceptible to Rowhammer.