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CVE-2026-89903

Estado: RecibidaAlta (7.8)—

In the Linux kernel, the following vulnerability has been resolved:

LoongArch: Do not save/restore percpu base register in rethook trampoline

The rethook trampoline saves $r21 ($u0), the percpu base, into its frame at entry and restores it at exit. Inbetween rethook_trampoline_handler() may schedule via preempt_enable_notrace().

If the task migrates to another CPU, the frame's $r21 holds the old CPU's percpu base, and restoring it poisons $r21 on the new CPU. Until the next user->kernel transition heals $r21, all this_cpu_*() accesses (runqueues, RCU per-CPU data, timer tick programming, FPU ownership) hit the wrong CPU's percpu area.

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Under kretprobe-heavy preemptible load this can corrupt scheduler and timer state: scheduling-while-atomic splats, wrong-CPU RCU warnings, WARN_ON_ONCE(rq != this_rq()) in nohz_balance_exit_idle(), and CPUs parking in the idle loop with the constant timer never re-armed (hard lockup). Reproduces on a Loongson-3A6000 with kretprobes on VFS paths plus heavy file churn (OS install / unsquashfs).

By convention $r21 always holds the current CPU's percpu base in kernel mode: SAVE_SOME() at exception entry reloads it only when coming from user mode, and RESTORE_SOME() restores it only when returning to user mode; the context-switch path never writes it. Therefore the live $r21 at trampoline exit is already correct, and nothing inbetween can change it legitimately (kernel C code cannot write a global register variable). The same flaw existed even in the pre-rethook kretprobe trampoline since v6.3; it was carried over when rethook replaced it. Drop both the save and the restore here. Drop the restore is enough to solve the issue, and drop the save is to keep the code tidy and no need to clear it.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad local en kernel Linux (AV:L/PR:L) que permite corrupción de estado crítico del sistema mediante manipulación de registros percpu en trampoline de rethook, causando DoS y corrupción de datos de scheduler/timer bajo carga preemptible.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Threat Intelligence ProgramRestrict File and Directory PermissionsRemote Data StorageFilter Network TrafficExecution PreventionEncrypt Sensitive Information

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux KernelAI

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-89903",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.8,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 1.8
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
              "lessThan": "a03b5e7483ad2c33ba5dd2adb8552e84bfee8fe2",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
              "lessThan": "8f15e95b438bc6b3c9f23a33c9a0d0678ebd1dc8",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
              "lessThan": "266ffc92e68593759adfe3d58f188773d32782c3",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
              "lessThan": "c048b0a3c0836c4b1bef4b51d355d27090bf6790",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "3f5536860086d906b01ec5ed68cf50c7edcc40af",
              "lessThan": "c3f2feace5e4f4b01b68b9f947b19adb4155c32e",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "arch/loongarch/kernel/rethook_trampoline.S"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.3"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.3",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.110",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "status": "unaffected",
              "version": "7.2.5",
              "versionType": "semver",
              "lessThanOrEqual": "7.2.*"
            },
            {
              "status": "unaffected",
              "version": "7.3-rc2",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "arch/loongarch/kernel/rethook_trampoline.S"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-09-16T11:16:59.257",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/266ffc92e68593759adfe3d58f188773d32782c3",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/8f15e95b438bc6b3c9f23a33c9a0d0678ebd1dc8",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/a03b5e7483ad2c33ba5dd2adb8552e84bfee8fe2",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/c048b0a3c0836c4b1bef4b51d355d27090bf6790",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/c3f2feace5e4f4b01b68b9f947b19adb4155c32e",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nLoongArch: Do not save/restore percpu base register in rethook trampoline\n\nThe rethook trampoline saves $r21 ($u0), the percpu base, into its frame\nat entry and restores it at exit. Inbetween rethook_trampoline_handler()\nmay schedule via preempt_enable_notrace().\n\nIf the task migrates to another CPU, the frame's $r21 holds the old\nCPU's percpu base, and restoring it poisons $r21 on the new CPU. Until\nthe next user->kernel transition heals $r21, all this_cpu_*() accesses\n(runqueues, RCU per-CPU data, timer tick programming, FPU ownership)\nhit the wrong CPU's percpu area.\n\nUnder kretprobe-heavy preemptible load this can corrupt scheduler and\ntimer state: scheduling-while-atomic splats, wrong-CPU RCU warnings,\nWARN_ON_ONCE(rq != this_rq()) in nohz_balance_exit_idle(), and CPUs\nparking in the idle loop with the constant timer never re-armed (hard\nlockup). Reproduces on a Loongson-3A6000 with kretprobes on VFS paths\nplus heavy file churn (OS install / unsquashfs).\n\nBy convention $r21 always holds the current CPU's percpu base in kernel\nmode: SAVE_SOME() at exception entry reloads it only when coming from\nuser mode, and RESTORE_SOME() restores it only when returning to user\nmode; the context-switch path never writes it. Therefore the live $r21\nat trampoline exit is already correct, and nothing inbetween can change\nit legitimately (kernel C code cannot write a global register variable).\nThe same flaw existed even in the pre-rethook kretprobe trampoline since\nv6.3; it was carried over when rethook replaced it. Drop both the save\nand the restore here. Drop the restore is enough to solve the issue, and\ndrop the save is to keep the code tidy and no need to clear it."
    }
  ],
  "lastModified": "2026-09-16T15:18:16.433",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}