Execution Unit Scheduler Contention Side-Channel Vulnerability on AMD Processors

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

Summary​

CVE-2021-46778
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.

Affected Products ​

Desktop

• AMD Ryzen™ 2000 series Desktop processors
• AMD Ryzen™ 3000 Series Desktop processors
• AMD Ryzen™ 5000 Series Desktop processors
• AMD Ryzen™ 4000 Series Desktop processors with Radeon™ graphics
• AMD Ryzen™ 5000 Series Desktop processors with Radeon™ graphics

High-End Desktop (HEDT)

• 2nd Gen AMD Ryzen™ Threadripper™ processors
• 3rd Gen AMD Ryzen™ Threadripper™ processors

Workstation

• AMD Ryzen™ Threadripper™ PRO processors

Mobile

• AMD Athlon™ 3000 Series Mobile processors with Radeon™ graphics
• AMD Ryzen™ 2000 Series Mobile processors
• AMD Ryzen™ 3000 Series Mobile processors, 2nd Gen AMD Ryzen™ 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

Chromebook

• AMD Athlon™ 3000 Series Mobile processors with Radeon™ graphics
• AMD Athlon™ Mobile processors with Radeon™ graphics
• AMD Ryzen™ 3000 Series Mobile processors with Radeon™ graphics

Server

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

Mitigation​

AMD recommends software developers employ existing best practices1,2, 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. BearSSL - Constant-Time Crypto
2. A beginner's guide to constant-time cryptography

Revisions​

Revision Date	Description
08-09-2022	Initial publication

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