bpf: Fix softlockup in arena_map_free on 64k page kernel

{
  "id": "ce5ab91a9dc6227ca1ecd6b8b69b5de0fc4e9d39b62f1fc45f4c105dfa3ed447",
  "url": "https://osv.dev/vulnerability/CVE-2025-21851",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "bpf: Fix softlockup in arena_map_free on 64k page kernel",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: bpf: Fix softlockup in arena_map_free on 64k page kernel On an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y, arena_htab tests cause a segmentation fault and soft lockup. The same failure is not observed with 4k pages on aarch64. It turns out arena_map_free() is calling apply_to_existing_page_range() with the address returned by bpf_arena_get_kern_vm_start(). If this address is not page-aligned the code ends up calling apply_to_pte_range() with that unaligned address causing soft lockup. Fix it by round up GUARD_SZ to PAGE_SIZE << 1 so that the division by 2 in bpf_arena_get_kern_vm_start() returns a page-aligned value.",
    "evidence": "osv:CVE-2025-21851",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.17",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.13.5",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-21851",
      "aliases": [
        "CVE-2025-21851"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "c1f3f3892d4526f18aaeffdb6068ce861e793ee3"
                },
                {
                  "fixed": "787d556a3de447e70964a4bdeba9196f62a62b1e"
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                {
                  "fixed": "517e8a7835e8cfb398a0aeb0133de50e31cae32b"
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          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21851.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.9.0"
                },
                {
                  "fixed": "6.12.17"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.13.5"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21851.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:32.145628971Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/517e8a7835e8cfb398a0aeb0133de50e31cae32b",
        "https://git.kernel.org/stable/c/787d556a3de447e70964a4bdeba9196f62a62b1e",
        "https://git.kernel.org/stable/c/c1f3f3892d4526f18aaeffdb6068ce861e793ee3",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21851.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-21851",
        "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/2025/21xxx/CVE-2025-21851.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-21851",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 498840,
  "published_at": "2025-03-12T09:42:06.48+00:00"
}