x86/fpu: Clear XSTATE_BV[i] in guest XSAVE state whenever XFD[i]=1

{
  "id": "9a610ca3bc10d419776938741cdf9932e2b4070b0e8bfaa107209b1e103e8a1f",
  "url": "https://osv.dev/vulnerability/CVE-2026-23005",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "x86/fpu: Clear XSTATE_BV[i] in guest XSAVE state whenever XFD[i]=1",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Clear XSTATE_BV[i] in guest XSAVE state whenever XFD[i]=1 When loading guest XSAVE state via KVM_SET_XSAVE, and when updating XFD in response to a guest WRMSR, clear XFD-disabled features in the saved (or to be restored) XSTATE_BV to ensure KVM doesn't attempt to load state for features that are disabled via the guest's XFD. Because the kernel executes XRSTOR with the guest's XFD, saving XSTATE_BV[i]=1 with XFD[i]=1 will cause XRSTOR to #NM and panic the kernel. E.g. if fpu_update_guest_xfd() sets XFD without clearing XSTATE_BV: ------------[ cut here ]------------ WARNING: arch/x86/kernel/traps.c:1524 at exc_device_not_available+0x101/0x110, CPU#29: amx_test/848 Modules linked in: kvm_intel kvm irqbypass CPU: 29 UID: 1000 PID: 848 Comm: amx_test Not tainted 6.19.0-rc2-ffa07f7fd437-x86_amx_nm_xfd_non_init-vm #171 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:exc_device_not_available+0x101/0x110 Call Trace: asm_exc_device_not_available+0x1a/0x20 RIP: 0010:restore_fpregs_from_fpstate+0x36/0x90 switch_fpu_return+0x4a/0xb0 kvm_arch_vcpu_ioctl_run+0x1245/0x1e40 [kvm] kvm_vcpu_ioctl+0x2c3/0x8f0 [kvm] __x64_sys_ioctl+0x8f/0xd0 do_syscall_64+0x62/0x940 entry_SYSCALL_64_after_hwframe+0x4b/0x53 ---[ end trace 0000000000000000 ]--- This can happen if the guest executes WRMSR(MSR_IA32_XFD) to set XFD[18] = 1, and a host IRQ triggers kernel_fpu_begin() prior to the vmexi",
    "evidence": "osv:CVE-2026-23005",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.162",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.122",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.67",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.7",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-23005",
      "aliases": [
        "CVE-2026-23005"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "820a6ee944e74e57255ac2e90916ecdaade57b95"
                },
                {
                  "fixed": "b5995c01ba53d84182ecb9492fc4d91cfe8a362d"
                },
                {
                  "fixed": "1e2848bda819af569dfe7ab186223855e092a2cb"
                },
                {
                  "fixed": "f577508cc8a0adb8b4ebe9480bba7683b6149930"
                },
                {
                  "fixed": "eea6f395ca502c4528314c8112da9b5d65f685eb"
                },
                {
                  "fixed": "b45f721775947a84996deb5c661602254ce25ce6"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23005.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.17.0"
                },
                {
                  "fixed": "6.1.162"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.122"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.67"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.7"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23005.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:42.258431170Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://git.kernel.org/stable/c/1e2848bda819af569dfe7ab186223855e092a2cb",
        "https://git.kernel.org/stable/c/b45f721775947a84996deb5c661602254ce25ce6",
        "https://git.kernel.org/stable/c/b5995c01ba53d84182ecb9492fc4d91cfe8a362d",
        "https://git.kernel.org/stable/c/eea6f395ca502c4528314c8112da9b5d65f685eb",
        "https://git.kernel.org/stable/c/f577508cc8a0adb8b4ebe9480bba7683b6149930",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23005.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-23005",
        "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/2026/23xxx/CVE-2026-23005.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-23005",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 510125,
  "published_at": "2026-01-25T14:36:19.021+00:00"
}