{
  "finding_id": "DF-5557",
  "status": "untested",
  "reproduced": false,
  "impact": "none",
  "confidence": "likely",
  "verdict": "Code-divergence certain by inspection (vkernel npxprobemask at sys/platform/vkernel64/x86_64/npx.c:120 stores the raw FXSAVE MXCSR_MASK word with no zero fallback, identical to pc64s DF-5526), but triggering it requires hardware whose FXSAVE reports MXCSR_MASK==0; the audit guests FXSAVE reports a non-zero mask, so no runtime reproduction is possible on the available rig. Impact if it fires is correctness only: every FP restore force-masks MXCSR to 0, unmasking all SIMD exceptions and SIGFPE-ing the first SSE instruction of each process. Info severity hardening twin; fix is the SDM-recommended 0xFFBF fallback.",
  "exploit_chain": "",
  "evidence": "README.md (full analysis + fix diff); no runtime artifacts \u2014 condition is hardware-dependent and absent on the rig",
  "kernel_refs": [
    "sys/platform/vkernel64/x86_64/npx.c:120",
    "sys/platform/vkernel64/x86_64/npx.c:341",
    "sys/platform/vkernel64/x86_64/npx.c:218",
    "sys/platform/pc64/x86_64/npx.c:126"
  ],
  "poc_changes": "none (no PoC authored: hardware precondition not satisfiable on the rig)",
  "attempts": 0,
  "guest_uname": "DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64",
  "runtime_sec": 0,
  "guest_dirty": 0,
  "build_cmd": "",
  "run_cmd": "",
  "code_hash": "",
  "notes": "Twin of DF-5526 (pc64, same pass). Should be fixed in both files with one upstream commit.",
  "recommended_fix": "npxprobemask(): if the probed MXCSR mask word is 0, fall back to 0xFFBF",
  "fix_status": "not_tested",
  "fix_baseline_reproduced": false,
  "fix_patched_reproduced": false,
  "fix_verdict": "n/a \u2014 no reproduction possible on available hardware",
  "fix_evidence": "n/a"
}