A contention-based side-channel vulnerability on some AMD CPUs using simultaneous multithreading (SMT) may allow an attacker to measure the contention level on scheduler queues, thereby leading to the potential leakage of sensitive information.

Execution unit scheduler contention may lead to a side channel vulnerability found on AMD CPU microarchitectures codenamed “Zen 1”, “Zen 2” and “Zen 3” that use simultaneous multithreading (SMT). By measuring the contention level on scheduler queues, an attacker may potentially leak sensitive information.

References
[1] https://www.amd.com/en/corporate/product-security/bulletin/amd-sb-1039
[2] https://www.bearssl.org/constanttime.html
[3] https://www.chosenplaintext.ca/articles/beginners-guide-constant-time-cryptography.html