Some older AMD CPUs have bug that breaks RdRand randomness

Posted on Wednesday, May 08 2019 @ 10:36 CEST by Thomas De Maesschalck
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Linux tech site Phoronix pulls attention to a loss of randomness bug with some of AMD's previous-generation processors. It seems the Zen generation is not affected, this bug seems limited to Excavator era processors so the impact is likely small as these chips have been on the market for many years.

As the site reports, the chip starts returning non-random data (when random data is expected) via the RdRand instruction following a suspend/resume cycle.
Referenced is this bug report outlining that the RdRand instruction on an older AMD A6-6310 processor isn't properly behaving following a suspend/resume. By avoiding RdRand usage on the system as part of generating a UUID, the reported systemd issue no longer happens.
Interestingly, the issue first got identified in 2014 but it was wrongly diagnosed as a BIOS bug instead of an issue with AMD's CPUs.

About the Author

Thomas De Maesschalck

Thomas has been messing with computer since early childhood and firmly believes the Internet is the best thing since sliced bread. Enjoys playing with new tech, is fascinated by science, and passionate about financial markets. When not behind a computer, he can be found with running shoes on or lifting heavy weights in the weight room.

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