Linux Kernel Logic Allowed Spectre Attack On Major Cloud Provider

The Spectre vulnerability that has haunted hardware and software makers since 2018 continues to defy efforts to bury it.

On Thursday, Eduardo (sirdarckcat) Vela Nava, from Google’s product security response team, disclosed a Spectre-related flaw in version 6.2 of the Linux kernel.

The bug, designated medium severity, was initially reported to cloud service providers – those most likely to be affected – on December 31, 2022, and was patched in Linux on February 27, 2023.

“The kernel failed to protect applications that attempted to protect against Spectre v2, leaving them open to attack from other processes running on the same physical core in another hyperthread,” the vulnerability disclosure explains. The consequence of that attack is potential information exposure (e.g., leaked private keys) through this pernicous problem.

The moniker Spectre [PDF] describes a set of vulnerabilities that abuse speculative execution, a processor performance optimization in which potential instructions are executed in advance to save time.

It’s timing, however, that animates Spectre. Spectre v2 – the variant implicated in this particular vulnerability – relies on timing side-channels to measure the misprediction rates of indirect branch prediction in order to infer the contents of protected memory. That’s far from optimal in a cloud environment with shared hardware.

Shortly after The Register first reported on the scramble to fix the Meltdown and Spectre bugs, Intel published details about Indirect Branch Restricted Speculation (IBRS), a mechanism to restrict speculation of indirect branches, which tell processors to start executing instructions at a

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