Execution Unit Scheduler Contention Side-Channel Vulnerability on AMD Processors

Bulletin ID: AMD-SB-1039
Potential Impact: Information Disclosure
Severity: Medium

Summary

Execution unit scheduler contention may lead to a side channel vulnerability found on AMD CPU microarchitectures codenamed “Zen 1”, “Zen 2”, “Zen 3” and “Zen 4” that use simultaneous multithreading (SMT). By measuring the contention level on scheduler queues an attacker may potentially leak sensitive information.

CVE Details

CVE-2021-46778

Execution unit scheduler contention may lead to a side channel vulnerability found on AMD CPU microarchitectures codenamed “Zen 1”, “Zen 2” ,“Zen 3” and "Zen 4" that use simultaneous multithreading (SMT).

Affected Products

Desktop

• AMD Athlon™ 2000 Series Desktop processors
• AMD Athlon™ 3000 Series Desktop processors
• AMD Ryzen™ 2000 Series Desktop processors
• AMD Ryzen™ 3000 Series Desktop processors
• AMD Ryzen™ 5000 Series Desktop processors
• AMD Ryzen™ 7000 Series Desktop processors
• AMD Ryzen™ 3000 Series Desktop processors with Radeon™ Graphics
• AMD Ryzen™ 4000 Series Desktop processors with Radeon™ Graphics
• AMD Ryzen™ 5000 Series Desktop processors with Radeon™ Graphics

High-End Desktop (HEDT)

• AMD Ryzen™ Threadripper™ 2000 Series processors
• AMD Ryzen™ Threadripper™ 3000 Series processors
• AMD Ryzen™ Threadripper™ 7000 Series processors

Workstation

• AMD Ryzen™ Threadripper™ PRO 3000 Series processors
• AMD Ryzen™ Threadripper™ PRO 5000 Series processors
• AMD Ryzen™ Threadripper™ PRO 7000 Series processors

Mobile

• AMD Ryzen™ 2000 Series Mobile processors with Radeon™ Graphics
• AMD Athlon™ 3000 Series Mobile processors with Radeon™ Graphics
• AMD Ryzen™ 3000 Series Mobile processors with Radeon™ Graphics
• AMD Ryzen™ 4000 Series Mobile processors with Radeon™ Graphics
• AMD Ryzen™ 5000 Series Mobile processors with Radeon™ Graphics
• AMD Ryzen™ 6000 Series Mobile processors with Radeon™ Graphics
• AMD Ryzen™ 7000 Series Mobile processors with Radeon™ Graphics
• AMD Ryzen™ 8000 Series Mobile processors with Radeon™ Graphics

Chromebook

• AMD Athlon™ 3000 Series Mobile processor with Radeon™ Graphics
• AMD Athlon™ 7000 Series Mobile processor with Radeon™ Graphics
• AMD Ryzen™ 3000 Series Mobile processor with Radeon™ Graphics
• AMD Ryzen™ 5000 Series Mobile processor with Radeon™ Graphics
• AMD Ryzen™ 7000 Series Mobile processor with Radeon™ Graphics

Server

• 1st Gen AMD EPYC™ processors
• 2nd Gen AMD EPYC™ processors
• 3rd Gen AMD EPYC™ processors 
• 4th Gen AMD EPYC™ processors

Mitigation

AMD recommends software developers employ existing best practices^1,2, including constant-time algorithms and avoiding secret-dependent control flows where appropriate to help mitigate this potential vulnerability.

Acknowledgement

AMD thanks the following for reporting these issues and engaging in coordinated vulnerability disclosure: 

CVE-2021-46778: 

• Stefan Gast, Daniel Gruss, Jonas Jiffinger and Martin Schwarzl of Lamarr Security Researcher/Graz University of Technology
• Simone Franza, Andreas Kogler and Markus Kostl of Graz University of Technology
• Gururaj Saileshwar of Georgia Institute of Technology

References

1. https://www.bearssl.org/constanttime.html
2. https://www.chosenplaintext.ca/articles/beginners-guide-constant-time-cryptography.html

Revisions

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