[Bug 283187] dev/random doesn't seem to utilize hardware feature(s) on AMD Zen family

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=283187

            Bug ID: 283187
           Summary: dev/random doesn't seem to utilize hardware feature(s)
                    on AMD Zen family
           Product: Base System
           Version: 14.1-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: diizzy@FreeBSD.org
                CC: cem@freebsd.org, delphij@FreeBSD.org,
                    emaste@freebsd.org, glebius@FreeBSD.org,
                    gordon@FreeBSD.org, markm@FreeBSD.org

Hi,

Maybe I'm reading the code incorrectly and misunderstand how
kern.random.random_sources is supposed to work but from what I can tell it
doesn't seem like the kernel is using RDSEED (and RDRAND) which is available on
AMD Zen CPUs?

# sysctl kern.random.random_sources
kern.random.random_sources:

References:
https://www.amd.com/content/dam/amd/en/documents/developer/amd-secure-random-number-generator-library-2.0-whitepaper.pdf
https://www.uops.info/html-instr/RDSEED_R64.html

dmesg output:

CPU: AMD Ryzen 9 7900 12-Core Processor              (3693.12-MHz K8-class CPU)
  Origin="AuthenticAMD"  Id=0xa60f12  Family=0x19  Model=0x61  Stepping=2
 
Features=0x178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,MMX,FXSR,SSE,SSE2,HTT>
 
Features2=0x7ef8320b<SSE3,PCLMULQDQ,MON,SSSE3,FMA,CX16,SSE4.1,SSE4.2,x2APIC,MOVBE,POPCNT,AESNI,XSAVE,OSXSAVE,AVX,F16C,RDRAND>
  AMD Features=0x2e500800<SYSCALL,NX,MMX+,FFXSR,Page1GB,RDTSCP,LM>
  AMD
Features2=0x75c237ff<LAHF,CMP,SVM,ExtAPIC,CR8,ABM,SSE4A,MAS,Prefetch,OSVW,IBS,SKINIT,WDT,TCE,Topology,PCXC,PNXC,DBE,PL2I,MWAITX,ADMSKX>
  Structured Extended
Features=0xf1bf97a9<FSGSBASE,BMI1,AVX2,SMEP,BMI2,ERMS,INVPCID,PQM,PQE,AVX512F,AVX512DQ,RDSEED,ADX,SMAP,AVX512IFMA,CLFLUSHOPT,CLWB,AVX512CD,SHA,AVX512BW,AVX512VL>
  Structured Extended
Features2=0x405fde<AVX512VBMI,UMIP,PKU,OSPKE,AVX512VBMI2,GFNI,VAES,VPCLMULQDQ,AVX512VNNI,AVX512BITALG,AVX512VPOPCNTDQ,RDPID>
  Structured Extended Features3=0x10000010<FSRM,L1DFL>
  XSAVE Features=0xf<XSAVEOPT,XSAVEC,XINUSE,XSAVES>
  AMD Extended Feature Extensions ID
EBX=0x791ef257<CLZERO,IRPerf,XSaveErPtr,RDPRU,BE,WBNOINVD,IBPB,INT_WBINVD,IBRS,STIBP,STIBP_ALWAYSON,PREFER_IBRS,SAMEMODE_IBRS,NOLMSLE,SSBD,CPPC,PSFD,BTC_NO,IBPB_RET>
  SVM: NP,NRIP,VClean,AFlush,DAssist,NAsids=32768
  TSC: P-state invariant, performance statistics

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