x86/fpu: Ensure XFD state on signal delivery

{
  "id": "24a6061b255b0f68d737bd718f69cfc41bb5060ef594ea64e93106f8f6854bae",
  "url": "https://osv.dev/vulnerability/CVE-2025-68171",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "x86/fpu: Ensure XFD state on signal delivery",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Ensure XFD state on signal delivery Sean reported [1] the following splat when running KVM tests: WARNING: CPU: 232 PID: 15391 at xfd_validate_state+0x65/0x70 Call Trace: fpu__clear_user_states+0x9c/0x100 arch_do_signal_or_restart+0x142/0x210 exit_to_user_mode_loop+0x55/0x100 do_syscall_64+0x205/0x2c0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Chao further identified [2] a reproducible scenario involving signal delivery: a non-AMX task is preempted by an AMX-enabled task which modifies the XFD MSR. When the non-AMX task resumes and reloads XSTATE with init values, a warning is triggered due to a mismatch between fpstate::xfd and the CPU's current XFD state. fpu__clear_user_states() does not currently re-synchronize the XFD state after such preemption. Invoke xfd_update_state() which detects and corrects the mismatch if there is a dynamic feature. This also benefits the sigreturn path, as fpu__restore_sig() may call fpu__clear_user_states() when the sigframe is inaccessible. [ dhansen: minor changelog munging ]",
    "evidence": "osv:CVE-2025-68171",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
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        "prerequisites": [],
        "fixed_versions": [
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            "evidence": "/affected/1/ranges"
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    "severity": "high",
    "structured": {
      "id": "CVE-2025-68171",
      "aliases": [
        "CVE-2025-68171"
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      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
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      ],
      "modified": "2026-10-28T02:30:38.422603388Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/1811c610653c0cd21cc9add14595b7cffaeca511",
        "https://git.kernel.org/stable/c/388eff894d6bc5f921e9bfff0e4b0ab2684a96e9",
        "https://git.kernel.org/stable/c/3f735419c4b43cde42e6d408db39137b82474e31",
        "https://git.kernel.org/stable/c/5b2619b488f1d08b960c43c6468dd0759e8b3035",
        "https://git.kernel.org/stable/c/eefbfb722042fc9210d2e0ac2b063fd1abf51895",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/68xxx/CVE-2025-68171.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-68171",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/68xxx/CVE-2025-68171.json"
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        "value": "CVE-2025-68171",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
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  "source_id": "core-osv",
  "document_id": 505476,
  "published_at": "2025-12-16T13:42:51.121+00:00"
}