AMD Details "SQUIP" Side Channel Vulnerability For Zen's Execution Unit Scheduler

Written by Michael Larabel in AMD on 9 August 2022 at 02:10 PM EDT. 54 Comments
In addition to Intel's busy Patch Tuesday, AMD today made public CVE-2021-46778 that university researchers have dubbed the "SQUIP" attack as a side channel vulnerability affecting the execution unit scheduler across Zen 1/2/3 processors.

Researchers discovered that execution unit scheduler contention could lead to a side channel vulnerability on AMD Zen 1, Zen 2, and Zen 3 processors -- across all Ryzen / Threadripper / EPYC generations to this point. This side-channel vulnerability exists only when SMT is active and relies on measuring the contention level of scheduler queues in order to leak sensitive information.

AMD isn't releasing any new kernel mitigations or microcode workarounds for this "SQUIP" vulnerability but their guidance simply notes:
AMD recommends software developers employ existing best practices, including constant-time algorithms and avoiding secret-dependent control flows where appropriate to help mitigate this potential vulnerability.

More details on this CVE-2021-46778 / SQUIP vulnerability via

The researchers from Lamarr Security Research, Graz University of Technology, and Georgia Institute of Technology have published their SQUIP whitepaper with more details on this new side-channel attack.
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