Thread

AMD's random number generator can't generate a 0?

288 points · 220 comments · BruceEel

349ru3h4f03 · 1790075025 · focus · HN ↗
<a href="https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7055.html" rel="nofollow">https://www.amd.com/en/resources/product-security/bulletin/a...
1. peri-cl · 1790075489 · focus · HN ↗
  The OP says they discovered this on a Zen 2, which is not covered by that bulletin (?)
  [edit to add]: Also, the bulletin is solely about RDSEED zeros, whereas the OP is also reporting RDRAND zeroes.
  1. ciupicri · 1790077284 · focus · HN ↗
    Older AMD processors had issues as well:
    <a href="https://github.com/systemd/systemd/pull/12536/commits/1c53d4a070edbec8ad2d384ba0014d0eb6bae077" rel="nofollow">https://github.com/systemd/systemd/pull/12536/commits/1c53d4...
    [deleted] · 1790079594 · focus · HN ↗
    [deleted]
    peri-cl · 1790080087 · focus · HN ↗
    That one's insidious!
    I found the thread about it,
    <a href="https://news.ycombinator.com/item?id=19848953">https://news.ycombinator.com/item?id=19848953
    Yikes at this: "I am so glad I resisted pressure from engineers working at Intel to let /dev/random in Linux rely blindly on the output of the RDRAND instructure." -Theodore Ts'o (2013)
    matja · 1790080491 · focus · HN ↗
    Why does systemd use architecture-specific instructions rather than using the kernel-provided random interface in the first place?
    claudex · 1790081320 · focus · HN ↗
    It was removed later <a href="https://github.com/systemd/systemd/commit/ffa047a03e4c5f6bd3af73b7eecb99cd230fe204" rel="nofollow">https://github.com/systemd/systemd/commit/ffa047a03e4c5f6bd3...

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