x86/fpu: Ensure shadow stack is active before "getting" registers

{
  "id": "59f03d42e5804d4bc56d57915a2cbd623f0c9d52ce2971c273322324fe9446f4",
  "url": "https://osv.dev/vulnerability/CVE-2025-21632",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "x86/fpu: Ensure shadow stack is active before \"getting\" registers",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Ensure shadow stack is active before \"getting\" registers The x86 shadow stack support has its own set of registers. Those registers are XSAVE-managed, but they are \"supervisor state components\" which means that userspace can not touch them with XSAVE/XRSTOR. It also means that they are not accessible from the existing ptrace ABI for XSAVE state. Thus, there is a new ptrace get/set interface for it. The regset code that ptrace uses provides an ->active() handler in addition to the get/set ones. For shadow stack this ->active() handler verifies that shadow stack is enabled via the ARCH_SHSTK_SHSTK bit in the thread struct. The ->active() handler is checked from some call sites of the regset get/set handlers, but not the ptrace ones. This was not understood when shadow stack support was put in place. As a result, both the set/get handlers can be called with XFEATURE_CET_USER in its init state, which would cause get_xsave_addr() to return NULL and trigger a WARN_ON(). The ssp_set() handler luckily has an ssp_active() check to avoid surprising the kernel with shadow stack behavior when the kernel is not ready for it (ARCH_SHSTK_SHSTK==0). That check just happened to avoid the warning. But the ->get() side wasn't so lucky. It can be called with shadow stacks disabled, triggering the warning in practice, as reported by Christina Schimpe: WARNING: CPU: 5 PID: 1773 at arch/x86/kernel/fpu/regset.c:198 ssp_get+",
    "evidence": "osv:CVE-2025-21632",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.6.72",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.10",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2025-21632",
      "aliases": [
        "CVE-2025-21632"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "2fab02b25ae7cf5f714ab456b03d9a3fe5ae98c9"
                },
                {
                  "fixed": "0a3a872214188e4268d31581ed0cd44508e038cf"
                },
                {
                  "fixed": "6bfe1fc22f462bec87422cdcbec4d7a2f43ff01d"
                },
                {
                  "fixed": "a9d9c33132d49329ada647e4514d210d15e31d81"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21632.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.6.0"
                },
                {
                  "fixed": "6.6.72"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.10"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21632.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:49.810428449Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0a3a872214188e4268d31581ed0cd44508e038cf",
        "https://git.kernel.org/stable/c/6bfe1fc22f462bec87422cdcbec4d7a2f43ff01d",
        "https://git.kernel.org/stable/c/a9d9c33132d49329ada647e4514d210d15e31d81",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21632.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-21632",
        "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-2025-21632.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-21632",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 518205,
  "published_at": "2025-01-19T10:17:50.721+00:00"
}