CVE-2021-46978

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To make sure eVMCS is\nmapped /vmx_set_nested_state() raises KVM_REQ_GET_NESTED_STATE_PAGES\nrequest.\n\nCommit f2c7ef3ba955 (\"KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES\non nested vmexit\") added KVM_REQ_GET_NESTED_STATE_PAGES clearing to\nnested_vmx_vmexit() to make sure MSR permission bitmap is not switched\nwhen an immediate exit from L2 to L1 happens right after migration (caused\nby a pending event, for example). Unfortunately, in the exact same\nsituation we still need to have eVMCS mapped so\nnested_sync_vmcs12_to_shadow() reflects changes in VMCS12 to eVMCS.\n\nAs a band-aid, restore nested_get_evmcs_page() when clearing\nKVM_REQ_GET_NESTED_STATE_PAGES in nested_vmx_vmexit(). The 'fix' is far\nfrom being ideal as we can't easily propagate possible failures and even if\nwe could, this is most likely already too late to do so. The whole\n'KVM_REQ_GET_NESTED_STATE_PAGES' idea for mapping eVMCS after migration\nseems to be fragile as we diverge too much from the 'native' path when\nvmptr loading happens on vmx_set_nested_state()."}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["arch/x86/kvm/vmx/nested.c"], "versions": [{"version": "0faceb7d6dda6f370ff1fa0464d7180f7e5cb417", "lessThan": "c8bf64e3fb77cc19bad146fbe26651985b117194", "status": "affected", "versionType": "git"}, {"version": "f2c7ef3ba9556d62a7e2bb23b563c6510007d55c", "lessThan": "200a45649ab7361bc80c70aebf7165b64f9a6c9f", "status": "affected", "versionType": "git"}, {"version": "f2c7ef3ba9556d62a7e2bb23b563c6510007d55c", "lessThan": "bd0e8455b85b651a4c77de9616e307129b15aaa7", "status": "affected", "versionType": "git"}, {"version": "f2c7ef3ba9556d62a7e2bb23b563c6510007d55c", "lessThan": 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nested state is migrated with\nvmx_get_nested_state()/vmx_set_nested_state() KVM can't map evmcs\npage right away: evmcs gpa is not 'struct kvm_vmx_nested_state_hdr'\nand we can't read it from VP assist page because userspace may decide\nto restore HV_X64_MSR_VP_ASSIST_PAGE after restoring nested state\n(and QEMU, for example, does exactly that). To make sure eVMCS is\nmapped /vmx_set_nested_state() raises KVM_REQ_GET_NESTED_STATE_PAGES\nrequest.\n\nCommit f2c7ef3ba955 (\"KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES\non nested vmexit\") added KVM_REQ_GET_NESTED_STATE_PAGES clearing to\nnested_vmx_vmexit() to make sure MSR permission bitmap is not switched\nwhen an immediate exit from L2 to L1 happens right after migration (caused\nby a pending event, for example). Unfortunately, in the exact same\nsituation we still need to have eVMCS mapped so\nnested_sync_vmcs12_to_shadow() reflects changes in VMCS12 to eVMCS.\n\nAs a band-aid, restore nested_get_evmcs_page() when clearing\nKVM_REQ_GET_NESTED_STATE_PAGES in nested_vmx_vmexit(). The 'fix' is far\nfrom being ideal as we can't easily propagate possible failures and even if\nwe could, this is most likely already too late to do so. The whole\n'KVM_REQ_GET_NESTED_STATE_PAGES' idea for mapping eVMCS after migration\nseems to be fragile as we diverge too much from the 'native' path when\nvmptr loading happens on vmx_set_nested_state()."}], "cpeApplicability": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.10.38", "versionStartIncluding": "5.10.13"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.11.22", "versionStartIncluding": "5.11"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.12.5", "versionStartIncluding": "5.11"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.13", "versionStartIncluding": "5.11"}], "operator": "OR"}]}], "providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-05-23T15:18:50.711Z"}}}, "cveMetadata": {"cveId": "CVE-2021-46978", "state": "PUBLISHED", "dateUpdated": "2026-05-23T15:18:50.711Z", "dateReserved": "2024-02-27T18:42:55.944Z", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "datePublished": "2024-02-28T08:13:09.106Z", "assignerShortName": "Linux"}, "dataVersion": "5.2"}

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To make sure eVMCS is\nmapped /vmx_set_nested_state() raises KVM_REQ_GET_NESTED_STATE_PAGES\nrequest.\n\nCommit f2c7ef3ba955 (\"KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES\non nested vmexit\") added KVM_REQ_GET_NESTED_STATE_PAGES clearing to\nnested_vmx_vmexit() to make sure MSR permission bitmap is not switched\nwhen an immediate exit from L2 to L1 happens right after migration (caused\nby a pending event, for example). Unfortunately, in the exact same\nsituation we still need to have eVMCS mapped so\nnested_sync_vmcs12_to_shadow() reflects changes in VMCS12 to eVMCS.\n\nAs a band-aid, restore nested_get_evmcs_page() when clearing\nKVM_REQ_GET_NESTED_STATE_PAGES in nested_vmx_vmexit(). The 'fix' is far\nfrom being ideal as we can't easily propagate possible failures and even if\nwe could, this is most likely already too late to do so. The whole\n'KVM_REQ_GET_NESTED_STATE_PAGES' idea for mapping eVMCS after migration\nseems to be fragile as we diverge too much from the 'native' path when\nvmptr loading happens on vmx_set_nested_state()."}, {"lang": "es", "value": "En el kernel de Linux, se resolvi\u00f3 la siguiente vulnerabilidad: KVM: nVMX: siempre intente asignar eVMCS despu\u00e9s de la migraci\u00f3n Cuando se utiliza VMCS iluminado y el estado anidado se migra con vmx_get_nested_state()/vmx_set_nested_state() KVM no puede asignar evmcs p\u00e1gina de inmediato: evmcs gpa no es 'struct kvm_vmx_nested_state_hdr' y no podemos leerlo desde la p\u00e1gina de asistencia de VP porque el espacio de usuario puede decidir restaurar HV_X64_MSR_VP_ASSIST_PAGE despu\u00e9s de restaurar el estado anidado (y QEMU, por ejemplo, hace exactamente eso). Para asegurarse de que eVMCS est\u00e9 asignado, /vmx_set_nested_state() genera la solicitud KVM_REQ_GET_NESTED_STATE_PAGES. el commit f2c7ef3ba955 (\"KVM: nSVM: cancelar KVM_REQ_GET_NESTED_STATE_PAGES en vmexit anidado\") agreg\u00f3 la limpieza KVM_REQ_GET_NESTED_STATE_PAGES a nested_vmx_vmexit() para asegurarse de que el mapa de bits del permiso MSR no se cambie cuando ocurre una salida inmediata de L2 a L1 justo despu\u00e9s de la migraci\u00f3n (causada por un evento pendiente, Por ejemplo). Desafortunadamente, en exactamente la misma situaci\u00f3n todav\u00eda necesitamos tener eVMCS mapeado para que nested_sync_vmcs12_to_shadow() refleje los cambios en VMCS12 a eVMCS. Como curita, restaure nested_get_evmcs_page() al borrar KVM_REQ_GET_NESTED_STATE_PAGES en nested_vmx_vmexit(). La \"soluci\u00f3n\" est\u00e1 lejos de ser ideal, ya que no podemos propagar f\u00e1cilmente posibles fallas e incluso si pudi\u00e9ramos, lo m\u00e1s probable es que ya sea demasiado tarde para hacerlo. Toda la idea 'KVM_REQ_GET_NESTED_STATE_PAGES' para mapear eVMCS despu\u00e9s de la migraci\u00f3n parece ser fr\u00e1gil ya que nos desviamos demasiado de la ruta 'nativa' cuando la carga de vmptr ocurre en vmx_set_nested_state()."}], "id": "CVE-2021-46978", "lastModified": "2026-06-17T04:16:03.320", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 7.8, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 5.9, "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2021-46978", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "total"}], "role": "CISA Coordinator", "timestamp": "2024-11-04T17:39:28.108559Z", "version": "2.0.3"}}]}, "published": "2024-02-28T09:15:37.183", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/200a45649ab7361bc80c70aebf7165b64f9a6c9f"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/bd0e8455b85b651a4c77de9616e307129b15aaa7"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/c8bf64e3fb77cc19bad146fbe26651985b117194"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/f5c7e8425f18fdb9bdb7d13340651d7876890329"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/200a45649ab7361bc80c70aebf7165b64f9a6c9f"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/bd0e8455b85b651a4c77de9616e307129b15aaa7"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/c8bf64e3fb77cc19bad146fbe26651985b117194"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/f5c7e8425f18fdb9bdb7d13340651d7876890329"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "NVD-CWE-noinfo"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: KVM: nVMX: Always make an attempt to map eVMCS after migration", "id": "2266919", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2266919"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.5", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "status": "draft"}, "cwe": "CWE-20", "details": ["In the Linux kernel, the following vulnerability has been resolved:\nKVM: nVMX: Always make an attempt to map eVMCS after migration\nWhen enlightened VMCS is in use and nested state is migrated with\nvmx_get_nested_state()/vmx_set_nested_state() KVM can't map evmcs\npage right away: evmcs gpa is not 'struct kvm_vmx_nested_state_hdr'\nand we can't read it from VP assist page because userspace may decide\nto restore HV_X64_MSR_VP_ASSIST_PAGE after restoring nested state\n(and QEMU, for example, does exactly that). To make sure eVMCS is\nmapped /vmx_set_nested_state() raises KVM_REQ_GET_NESTED_STATE_PAGES\nrequest.\nCommit f2c7ef3ba955 (\"KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES\non nested vmexit\") added KVM_REQ_GET_NESTED_STATE_PAGES clearing to\nnested_vmx_vmexit() to make sure MSR permission bitmap is not switched\nwhen an immediate exit from L2 to L1 happens right after migration (caused\nby a pending event, for example). Unfortunately, in the exact same\nsituation we still need to have eVMCS mapped so\nnested_sync_vmcs12_to_shadow() reflects changes in VMCS12 to eVMCS.\nAs a band-aid, restore nested_get_evmcs_page() when clearing\nKVM_REQ_GET_NESTED_STATE_PAGES in nested_vmx_vmexit(). The 'fix' is far\nfrom being ideal as we can't easily propagate possible failures and even if\nwe could, this is most likely already too late to do so. The whole\n'KVM_REQ_GET_NESTED_STATE_PAGES' idea for mapping eVMCS after migration\nseems to be fragile as we diverge too much from the 'native' path when\nvmptr loading happens on vmx_set_nested_state()."], "name": "CVE-2021-46978", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2024-02-28T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2021-46978\nhttps://nvd.nist.gov/vuln/detail/CVE-2021-46978\nhttps://lore.kernel.org/linux-cve-announce/2024022822-CVE-2021-46978-3516@gregkh/T/#u"], "threat_severity": "Low"}

{}