"The bug was uncovered by Meta engineer Gregory Price, and details were posted to a Linux kernel mailing list. Price wrote: "Under unknown architectural conditions, Zen5 chips running rdseed can produce (val=0,CF=1) as a "random" result over 10% of the time (when rdseed is successful). CF=1 indicates success, while val=0 is typically only produced when rdseed fails (CF=0).""
"If that's all Greek to you, allow me to decipher it. Put simply, RDSEED is designed to collect "environmental entropy," such as thermal and voltage noise, from the processor and use this to generate random numbers, similar to rolling a set of dice. Price is saying that about 10% of the time, running the code returns a 0, with no indication that something went wrong -- and the 0 would go on to be used for cryptographic purposes, compromising the security."
"It's like the system can't be bothered to roll any of the dice sometimes, but doesn't let anyone know! That's a very big deal because numbers that are meant to be random have a high chance of being predictable, and this will seriously affect the security of anything that uses these "unrandom" random numbers."
An RDSEED implementation flaw affects Zen 5 generation AMD processors and can return a zero value while signaling success about 10% of successful calls. RDSEED is intended to gather environmental entropy such as thermal and voltage noise to produce unpredictable random numbers for cryptographic use. Returning zero with a success flag produces low-entropy, predictable outputs that can compromise cryptographic operations and system security. The flaw impacts multiple product lines including EPYC 9005, Ryzen 9000 series, Ryzen AI and Threadripper 9000 families. Remediation work is reported to be in development.
Read at ZDNET
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