RDRAND issue

By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), August 10, 2019 4:15 pm
Room: Moderated Discussions
anonymou5 (no.delete@this.spam.com) on August 10, 2019 2:52 pm wrote:
> > Zen 2 with the rdrand bug
>
> Is Family 17h actually affected?

Yes. It might be (slightly) different from an earlier AMD rdrand issue, but yes, people definitely had problems on Zen 2. There's a microcode fix - it was apparently something stupid (again) where the random number generation wasn't properly initialized, and presumably the fix was simple.

See for example

heise.de Ryzen 3000 rdrand article

which is in German, but google translate makes good sense of it.

Basically, the broken AMD 'rdrand' returns a value of all-ones (which is not really all that random), but still claims that it's all working fine (by setting CF to 1). It's a serious functionality bug, and the fact that something like it has now happened at least twice is pretty sad.

Note that afaik there's no kernel bugzilla entry for the Zen 2 rdrand issue - it didn't affect the kernel. We do use rdrand, but not generally in a long loop, and we don't trust the result implicitly (so it gets used to initialize entropy data, and a completely broken rdrand does possibly weaken random data generation, but since we also have other sources of entropy, you're generally going to have a hard time really notice broken rdrand for the kernel (famous last words).

Don't use broken CPU's and trust the resulting keys regardless. The kernel is bring pretty careful, but not all tools necessarily are. The old AMD rdrand issue hit openssl, and the Zen 2 one hit at least systemd.

It really doesn't seem that bad in general - just very embarrassing, and showing that there was a decided lack of test coverage for rdrand inside of AMD.

If that's the only problem Zen 2 has, it would be a very good sign for AMD. But it's all new enough that we obviously don't have a ton of independent test coverage yet.

Linus
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EPYC SAP-SD 2-tier benchmark resultsMichael S2019/08/08 05:18 AM
  EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownMichael S2019/08/08 08:29 AM
    Wrong headline. Should be "SPECpower_ssj2008 - EPYC2 is in class of its own" (NT)Michael S2019/08/08 08:51 AM
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        EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownanon2019/08/09 02:00 AM
          EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownAlberto2019/08/09 03:09 AM
            EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownblue2019/08/09 08:47 AM
        EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownAlberto2019/08/09 02:12 AM
          EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownMaynard Handley2019/08/09 09:25 AM
            EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownDoug S2019/08/09 09:33 AM
              EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownanon2019/08/09 10:24 AM
            EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownAlberto2019/08/10 04:04 AM
          EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownanon.12019/08/09 05:30 PM
        EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownme2019/08/09 09:58 PM
      EPYC SAP-SD 2-tier benchmark results - EPYC2 is in class of its ownanon2019/08/09 12:47 AM
  EPYC SAP-SD 2-tier benchmark resultsLinus Torvalds2019/08/09 03:29 PM
    EPYC SAP-SD 2-tier benchmark resultsanon2019/08/10 07:20 AM
      EPYC SAP-SD 2-tier benchmark resultsme2019/08/10 07:36 AM
        EPYC SAP-SD 2-tier benchmark resultsanon2019/08/10 08:20 AM
          EPYC SAP-SD 2-tier benchmark resultsanon.12019/08/10 09:40 AM
            EPYC SAP-SD 2-tier benchmark resultsanon2019/08/10 10:38 AM
          EPYC SAP-SD 2-tier benchmark resultsblue2019/08/10 09:47 AM
        EPYC SAP-SD 2-tier benchmark resultsAdrian2019/08/10 10:43 AM
          EPYC SAP-SD 2-tier benchmark resultsme2019/08/10 11:06 AM
            EPYC SAP-SD 2-tier benchmark resultsMichael S2019/08/10 11:28 AM
    Big gotchas: poor specsjohn2019/08/10 10:54 AM
      Big gotchas: poor specsme2019/08/10 11:04 AM
      Big gotchas: poor specsanon2019/08/10 11:25 AM
        Big gotchas: poor specsLinus Torvalds2019/08/10 12:13 PM
          Big gotchas: poor specsanon2019/08/10 01:58 PM
          Big gotchas: poor caches2019/08/12 01:51 AM
            Big gotchas: poor caches2019/08/12 01:59 AM
            Big gotchas: poor cachesTravis Downs2019/08/12 09:15 AM
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            Big gotchas: poor cachesAndy N2019/08/12 06:45 PM
              Big gotchas: poor cachesanon2019/08/13 12:43 AM
          Big gotchas: poor specsJouni Osmala2019/08/12 10:18 PM
            Big gotchas: poor specsAdrian2019/08/12 11:58 PM
              Kernel compile 25-30s, noise 25-27dBJouni Osmala2019/08/13 04:00 AM
                Quiet and fast workstationsGian-Carlo Pascutto2019/08/13 06:00 AM
                  Quiet and fast workstationsAdrian2019/08/13 07:01 AM
                  Quiet and fast workstationsDavid Hess2019/08/13 01:51 PM
                    Quiet and fast workstationsGian-Carlo Pascutto2019/08/14 12:43 AM
                      Quiet and fast workstationsMichael S2019/08/14 02:09 AM
                        Quiet and fast workstationsGian-Carlo Pascutto2019/08/14 02:59 AM
                          Quiet and fast workstationsDavid Hess2019/08/14 06:05 PM
                        Quiet and fast workstationsDavid Hess2019/08/14 05:56 PM
                      Quiet and fast workstationsDavid Hess2019/08/14 06:30 PM
                  Passively cooled threadripper/xeon WJouni Osmala2019/08/15 03:12 AM
                    Passively cooled threadripper/xeon WAdrian2019/08/15 03:47 AM
                      Passively cooled threadripper/xeon WJouni Osmala2019/08/15 05:58 AM
                        Passively cooled threadripper/xeon WAdrian2019/08/16 12:12 AM
                          Passively cooled threadripper/xeon WAdrian2019/08/16 12:21 AM
                          Passively cooled threadripper/xeon WJouni osmala2019/08/16 09:46 AM
                            Passively cooled threadripper/xeon WGroo2019/08/16 12:07 PM
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                Kernel compile 25-30s, noise 25-27dBLinus Torvalds2019/08/13 12:12 PM
                  which graphics card?anonymous22019/08/13 12:52 PM
                    which graphics card?Linus Torvalds2019/08/13 01:12 PM
                  Kernel compile 25-30s, noise 25-27dBDoug S2019/08/13 03:22 PM
                    Kernel compile 25-30s, noise 25-27dBDavid Hess2019/08/14 06:38 PM
                  Kernel compile 25-30s, noise 25-27dBJouni Osmala2019/08/14 12:09 AM
                    AIOsGroo2019/08/14 07:19 AM
                      AIOsGian-Carlo Pascutto2019/08/14 08:52 AM
                        AIOsGroo2019/08/14 09:49 AM
                      AIOsBrett2019/08/14 02:02 PM
                    Kernel compile 25-30s, noise 25-27dBLinus Torvalds2019/08/14 11:10 AM
                  Kernel compile 25-30s, noise 25-27dBGian-Carlo Pascutto2019/08/14 01:33 AM
                    Kernel compile 25-30s, noise 25-27dBAdrian2019/08/14 05:06 AM
                      Kernel compile 25-30s, noise 25-27dBGian-Carlo Pascutto2019/08/14 09:01 AM
                      AMD Bios, etc..Anon2019/08/14 11:39 PM
                        AMD Bios, etc..hobold2019/08/15 07:10 AM
                          AMD Bios, etc..Anon2019/08/15 04:20 PM
                        AMD Bios, etc..Jan Olšan2019/08/15 08:49 AM
                          AMD Bios, etc..Adrian2019/08/15 09:16 AM
                          AMD Bios, etc..Gro2019/08/15 10:57 AM
                        AMD Bios, etc..David Hess2019/08/16 05:39 AM
      Big gotchas: poor specsAdrian2019/08/10 01:28 PM
      Big gotchas: poor specsDummond D. Slow2019/08/10 01:57 PM
        Big gotchas: poor specsanon22019/08/11 12:33 AM
          Big gotchas: poor specsblue2019/08/11 12:57 AM
          Big gotchas: poor specsAdrian2019/08/11 05:41 AM
            Big gotchas: poor specsaaron spink2019/08/12 09:45 AM
              Big gotchas: poor specsFoo_2019/08/12 11:02 AM
              Big gotchas: poor specsTravis Downs2019/08/12 11:26 AM
                Big gotchas: poor specsGabriele Svelto2019/08/13 09:48 AM
                Big gotchas: poor specsaaron spink2019/08/13 07:23 PM
                  Big gotchas: poor specsDoug S2019/08/13 11:15 PM
                    Big gotchas: poor specsGian-Carlo Pascutto2019/08/14 01:35 AM
                    Big gotchas: poor specsaaron spink2019/08/15 05:16 PM
                      Big gotchas: poor specsJouni Osmala2019/08/15 09:03 PM
                        Big gotchas: poor specsaaron spink2019/08/19 04:05 AM
                          Big gotchas: poor specsMichael S2019/08/19 04:37 AM
                            Big gotchas: poor specsRicardo B2019/08/19 05:40 PM
                              Big gotchas: poor specsAaron Spink2019/08/25 02:29 AM
              Big gotchas: poor specsAdrian2019/08/12 11:31 AM
              Big gotchas: poor specsJukka Larja2019/08/13 07:37 AM
              Big gotchas: poor specsLinus Torvalds2019/08/13 11:31 AM
          Big gotchas: poor specsDummond D. Slow2019/08/11 06:23 AM
      FX-9590 > i7-9700KGian-Carlo Pascutto2019/08/12 10:37 AM
    RDRAND issueanonymou52019/08/10 02:52 PM
      RDRAND issueLinus Torvalds2019/08/10 04:15 PM
        RDRAND issueGionatan Danti2019/08/11 01:35 AM
          RDRAND issueLinus Torvalds2019/08/11 10:43 AM
            RDRAND issueLinus Torvalds2019/08/11 11:05 AM
              RDRAND issue@never_released2019/08/11 11:10 AM
                RDRAND issueLinus Torvalds2019/08/11 01:13 PM
                  Err....Groo2019/08/11 06:47 PM
                    Err.... This is a zero content fud posteye roll2019/08/11 08:48 PM
                    Err....Brendan2019/08/11 08:50 PM
                    Err....Jukka Larja2019/08/12 07:38 AM
                  RDRAND issueJose2019/08/12 02:33 AM
              RDRAND issueGionatan Danti2019/08/11 02:12 PM
            RDRAND issueaaron spink2019/08/12 09:18 AM
      RDRAND issuename2019/08/11 09:35 AM
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