No HW RNG on general purpose Graviton Instances. WHY?

0

RDRAND is available on all of the x86 instances. The AArch64 equivalent RNDR is not exposed on general purpose Graviton instances. As a consequence, rngd.service struggles to start. The service is started multiple times on AWS Linux to force it to build up entropy using system jitter, which is as good as not having it.

... WHY?

https://bugs.rockylinux.org/view.php?id=5380

https://lwn.net/Articles/525459/

3 Answers
2

Graviton 2 doesn't support h/w RNG instructions. Graviton 3 does. We have it listed here: https://github.com/aws/aws-graviton-getting-started

answered a month ago
1

Well, apparently t4g is powered by Graviton 2 and c7g Graviton 3. Their respective arch are ARMv8.2-A and ARMv8.4-A. But RNDR has been introduced with ARMv8.5-A. Either this wiki article is wrong or Graviton processors are brewed with extra stuff.

Either way, Graviton 2 instances are left with no HW RNG.

David T
answered a month ago
0

But RNDR has been introduced with ARMv8.5-A. Either this wiki article is wrong or Graviton processors are brewed with extra stuff.

Graviton3 is based on Arm's Neoverse-V1 core which implements everything needed for Armv8.4-a plus some extras they pulled in from Armv8.5-a, such as the TRNG instructions. You can see the full list of features from the Tech Reference Manual for the V1 core. Its not uncommon for Arm when building core IP to have a base architecture it fully supports yet pull in bits of future architectures as needed due to customer needs. For what Graviton supports, consider https://github.com/aws/aws-graviton-getting-started the definitive guide, and please raise issues if something appears missing.

GeoffB
answered a month ago

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