arm64/fpsimd: Discard stale CPU state when handling SME traps

{
  "id": "5179b11c5ce8e51307c43337825f56f38fd8df6ef545d1771197b5774a97a9fe",
  "url": "https://osv.dev/vulnerability/CVE-2025-38170",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "arm64/fpsimd: Discard stale CPU state when handling SME traps",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: arm64/fpsimd: Discard stale CPU state when handling SME traps The logic for handling SME traps manipulates saved FPSIMD/SVE/SME state incorrectly, and a race with preemption can result in a task having TIF_SME set and TIF_FOREIGN_FPSTATE clear even though the live CPU state is stale (e.g. with SME traps enabled). This can result in warnings from do_sme_acc() where SME traps are not expected while TIF_SME is set: | /* With TIF_SME userspace shouldn't generate any traps */ | if (test_and_set_thread_flag(TIF_SME)) | WARN_ON(1); This is very similar to the SVE issue we fixed in commit: 751ecf6afd6568ad (\"arm64/sve: Discard stale CPU state when handling SVE traps\") The race can occur when the SME trap handler is preempted before and after manipulating the saved FPSIMD/SVE/SME state, starting and ending on the same CPU, e.g. | void do_sme_acc(unsigned long esr, struct pt_regs *regs) | { | // Trap on CPU 0 with TIF_SME clear, SME traps enabled | // task->fpsimd_cpu is 0. | // per_cpu_ptr(&fpsimd_last_state, 0) is task. | | ... | | // Preempted; migrated from CPU 0 to CPU 1. | // TIF_FOREIGN_FPSTATE is set. | | get_cpu_fpsimd_context(); | | /* With TIF_SME userspace shouldn't generate any traps */ | if (test_and_set_thread_flag(TIF_SME)) | WARN_ON(1); | | if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) { | unsigned long vq_minus_one = | sve_vq_from_vl(task_get_sme_vl(current)) - 1; | sme_set_vq(vq_minus_one); | | fpsimd_",
    "evidence": "osv:CVE-2025-38170",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.142",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.94",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.34",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.15.3",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2025-38170",
      "aliases": [
        "CVE-2025-38170"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                  "introduced": "8bd7f91c03d886f41d35f6108078d20be5a4a1bd"
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                {
                  "fixed": "de89368de3894a8db27caeb8fd902ba1c49f696a"
                },
                {
                  "fixed": "43be952e885476dafb74aa832c0847b2f4f650c6"
                },
                {
                  "fixed": "6103f9ba51a59afb5a0f32299c837377c5a5a693"
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                {
                  "fixed": "c4a4786d93e99517d6f10ed56b9ffba4ce88d3b3"
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                  "fixed": "d3eaab3c70905c5467e5c4ea403053d67505adeb"
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              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-38170.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.19.0"
                },
                {
                  "fixed": "6.1.142"
                }
              ]
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            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
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                {
                  "fixed": "6.6.94"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.34"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.15.3"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-38170.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:41.558786341Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/43be952e885476dafb74aa832c0847b2f4f650c6",
        "https://git.kernel.org/stable/c/6103f9ba51a59afb5a0f32299c837377c5a5a693",
        "https://git.kernel.org/stable/c/c4a4786d93e99517d6f10ed56b9ffba4ce88d3b3",
        "https://git.kernel.org/stable/c/d3eaab3c70905c5467e5c4ea403053d67505adeb",
        "https://git.kernel.org/stable/c/de89368de3894a8db27caeb8fd902ba1c49f696a",
        "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/38xxx/CVE-2025-38170.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-38170",
        "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/2025/38xxx/CVE-2025-38170.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-38170",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 508837,
  "published_at": "2025-07-03T08:36:09.012+00:00"
}