AMD CPUs May Transiently Execute Beyond Unconditional Direct Branch

Bulletin ID: AMD-SB-1026
Potential Impact: Data leakage
Severity: Medium

Summary

AMD is providing an update for one recommended mitigation, mitigation G-5, in the “Software Techniques for Managing Speculation on AMD processors” white paper. Mitigation G-5 helps address potential vulnerabilities associated with speculative behavior of branch instructions.

AMD processors may transiently execute instructions following an unconditional direct branch that may result in detectable cache activity. 

AMD is not aware of any active exploits in the wild that use this potential security vulnerability to exploit AMD products.

CVE Details

CVE-2021-26341

Some AMD CPUs may transiently execute beyond unconditional direct branches, which may potentially result in data leakage.

Affected Products

Desktop

• AMD Athlon™ X4 processor
• AMD Ryzen™ Threadripper™ PRO processor
• 2nd Gen AMD Ryzen™ Threadripper™ processors
• 3rd Gen AMD Ryzen™ Threadripper™ processors
• 7th Generation AMD A-Series APUs
• AMD Ryzen™ 2000 Series Desktop processors
• AMD Ryzen™ 3000 Series Desktop processors
• AMD Ryzen™ 4000 Series Desktop processors with Radeon™ graphics

Mobile

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

Server

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

Mitigation

AMD has provided guidance via an updated paper located here: https://www.amd.com/system/files/documents/software-techniques-for-managing-speculation.pdf

Acknowledgement

AMD thanks Pawel Wieczorkiewicz from grsecurity for reporting this issue.

References  

https://www.amd.com/system/files/documents/software-techniques-for-managing-speculation.pdf

Revisions

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