{
  "cveId": "CVE-2021-46978",
  "url": "https://patchblox.com/security/cve/CVE-2021-46978",
  "summary": "CVE-2021-46978 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-46978, released February 28, 2024. It is not reported as exploited. Patch Radar priority: High.",
  "title": "linux: In the Linux kernel, the following vulnerability has been resolved:  KVM: nVMX: Always make an attempt to map eVMCS a...",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  KVM: nVMX: Always make an attempt to map eVMCS after migration  When enlightened VMCS is in use and nested state is migrated with vmx_get_nested_state()/vmx_set_nested_state() KVM can\u0027t map evmcs page right away: evmcs gpa is not \u0027struct kvm_vmx_nested_state_hdr\u0027 and we can\u0027t read it from VP assist page because userspace may decide to restore HV_X64_MSR_VP_ASSIST_PAGE after restoring nested state (and QEMU, for example, does exactly that). To make sure eVMCS is mapped /vmx_set_nested_state() raises KVM_REQ_GET_NESTED_STATE_PAGES request.  Commit f2c7ef3ba955 (\u0022KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES on nested vmexit\u0022) added KVM_REQ_GET_NESTED_STATE_PAGES clearing to nested_vmx_vmexit() to make sure MSR permission bitmap is not switched when an immediate exit from L2 to L1 happens right after migration (caused by a pending event, for example). Unfortunately, in the exact same situation we still need to have eVMCS mapped so nested_sync_vmcs12_to_shadow() reflects changes in VMCS12 to eVMCS.  As a band-aid, restore nested_get_evmcs_page() when clearing KVM_REQ_GET_NESTED_STATE_PAGES in nested_vmx_vmexit(). The \u0027fix\u0027 is far from being ideal as we can\u0027t easily propagate possible failures and even if we could, this is most likely already too late to do so. The whole \u0027KVM_REQ_GET_NESTED_STATE_PAGES\u0027 idea for mapping eVMCS after migration seems to be fragile as we diverge too much from the \u0027native\u0027 path when vmptr loading happens on vmx_set_nested_state().",
  "published": "2024-02-28T09:15:37Z",
  "severity": "high",
  "cvss": 7.8,
  "cvssVector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
  "epss": 0.00241,
  "epssPercentile": 0.1532,
  "priority": "High",
  "priorityTier": 3,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 12.15 (bookworm)",
      "fixedVersion": "5.10.38-1",
      "fix": "DEBIAN-CVE-2021-46978",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-46978",
      "released": "2024-02-28T09:15:37Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 13.5 (trixie)",
      "fixedVersion": "5.10.38-1",
      "fix": "DEBIAN-CVE-2021-46978",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-46978",
      "released": "2024-02-28T09:15:37Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 14",
      "fixedVersion": "5.10.38-1",
      "fix": "DEBIAN-CVE-2021-46978",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-46978",
      "released": "2024-02-28T09:15:37Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-09T07:25:28Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}