CVE-2021-47450 (GCVE-0-2021-47450)

Vulnerability from cvelistv5 – Published: 2024-05-22 06:19 – Updated: 2026-08-05 08:47
VLAI
Title
KVM: arm64: Fix host stage-2 PGD refcount
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Fix host stage-2 PGD refcount The KVM page-table library refcounts the pages of concatenated stage-2 PGDs individually. However, when running KVM in protected mode, the host's stage-2 PGD is currently managed by EL2 as a single high-order compound page, which can cause the refcount of the tail pages to reach 0 when they shouldn't, hence corrupting the page-table. Fix this by introducing a new hyp_split_page() helper in the EL2 page allocator (matching the kernel's split_page() function), and make use of it from host_s2_zalloc_pages_exact().
Severity
8.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-05-22 18:46 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1025c8c0c6accfcbdc8f52ca1940160f65cd87d6 , < b372264c66ef78f2cab44e877fbd765ad6d24c39 (git)
Affected: 1025c8c0c6accfcbdc8f52ca1940160f65cd87d6 , < 1d58a17ef54599506d44c45ac95be27273a4d2b1 (git)
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Linux Linux Affected: 5.13
Unaffected: 0 , < 5.13 (semver)
Unaffected: 5.14.15 , ≤ 5.14.* (semver)
Unaffected: 5.15 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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      "status": "interim",
      "title": "SUSE CVE CVE-2021-47450",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-47450.json",
      "version": "54"
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    "vulnrichment": {
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              "orgId": "af854a3a-2127-422b-91ae-364da2661108",
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            "references": [
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                "url": "https://git.kernel.org/stable/c/b372264c66ef78f2cab44e877fbd765ad6d24c39"
              },
              {
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                ],
                "url": "https://git.kernel.org/stable/c/1d58a17ef54599506d44c45ac95be27273a4d2b1"
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            ],
            "title": "CVE Program Container"
          },
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2021-47450",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2024-05-22T18:46:22.813390Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
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            "providerMetadata": {
              "dateUpdated": "2024-05-22T18:46:50.839Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
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              "defaultStatus": "unaffected",
              "product": "Linux",
              "programFiles": [
                "arch/arm64/kvm/hyp/include/nvhe/gfp.h",
                "arch/arm64/kvm/hyp/nvhe/mem_protect.c",
                "arch/arm64/kvm/hyp/nvhe/page_alloc.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
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                  "lessThan": "b372264c66ef78f2cab44e877fbd765ad6d24c39",
                  "status": "affected",
                  "version": "1025c8c0c6accfcbdc8f52ca1940160f65cd87d6",
                  "versionType": "git"
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                  "status": "affected",
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            },
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              "product": "Linux",
              "programFiles": [
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
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                {
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                  "status": "unaffected",
                  "version": "0",
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                  "status": "unaffected",
                  "version": "5.14.15",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "5.15",
                  "versionType": "original_commit_for_fix"
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                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
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              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: arm64: Fix host stage-2 PGD refcount\n\nThe KVM page-table library refcounts the pages of concatenated stage-2\nPGDs individually. However, when running KVM in protected mode, the\nhost\u0027s stage-2 PGD is currently managed by EL2 as a single high-order\ncompound page, which can cause the refcount of the tail pages to reach 0\nwhen they shouldn\u0027t, hence corrupting the page-table.\n\nFix this by introducing a new hyp_split_page() helper in the EL2 page\nallocator (matching the kernel\u0027s split_page() function), and make use of\nit from host_s2_zalloc_pages_exact()."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "baseScore": 8.8,
                "baseSeverity": "HIGH",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
                "version": "3.1"
              },
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                  "lang": "en",
                  "value": "AV:L - The bug is in pKVM EL2 host stage-2 PGD refcounting and is reached via local host activity (host stage-2 faults, KVM/hyp share/donate paths), not via remote packet processing.\nAC:L - Once pKVM protected mode is enabled, emptying the last counted PTE in a concatenated PGD tail page deterministically drives that page\u0027s refcount to zero and frees it while it remains part of the live PGD; an attacker who can cause host stage-2 map/unmap churn can reliably provoke this.\nPR:L - On the primary pKVM deployment (e.g. Android), a normal local user who can drive host MMIO/KVM-related stage-2 updates can reach the vulnerable get/put_page path without needing real root in the init namespace.\nUI:N - No separate victim action is required; the attacker triggers the map/unmap sequence themselves.\nS:C - Corruption is of the EL2 host stage-2 page tables that enforce the pKVM isolation boundary between the host and the hypervisor/protected VMs, so impact crosses that security authority.\nC:H - Incorrectly freeing an in-use PGD page is a page-table UAF; reuse of that page can yield attacker-controlled stage-2 entries and arbitrary host/hyp memory disclosure across the pKVM boundary.\nI:H - The same PGD UAF enables installation of malicious stage-2 mappings and control-flow/memory integrity breaks in the hypervisor-managed host view of physical memory.\nA:H - Freeing or corrupting live host stage-2 PGD pages can panic EL2, oops the host, or otherwise crash the system."
                }
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          "providerMetadata": {
            "dateUpdated": "2026-08-05T08:47:53.018Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
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              "url": "https://git.kernel.org/stable/c/b372264c66ef78f2cab44e877fbd765ad6d24c39"
            },
            {
              "url": "https://git.kernel.org/stable/c/1d58a17ef54599506d44c45ac95be27273a4d2b1"
            }
          ],
          "title": "KVM: arm64: Fix host stage-2 PGD refcount",
          "x_generator": {
            "engine": "bippy-1.2.0"
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        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2021-47450",
        "datePublished": "2024-05-22T06:19:41.443Z",
        "dateReserved": "2024-05-21T14:58:30.832Z",
        "dateUpdated": "2026-08-05T08:47:53.018Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.