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CVE-2025-38508

Estado: ModificadaMedia (5.5)—

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

x86/sev: Use TSC_FACTOR for Secure TSC frequency calculation

When using Secure TSC, the GUEST_TSC_FREQ MSR reports a frequency based on the nominal P0 frequency, which deviates slightly (typically ~0.2%) from the actual mean TSC frequency due to clocking parameters.

Over extended VM uptime, this discrepancy accumulates, causing clock skew between the hypervisor and a SEV-SNP VM, leading to early timer interrupts as perceived by the guest.

The guest kernel relies on the reported nominal frequency for TSC-based timekeeping, while the actual frequency set during SNP_LAUNCH_START may differ.

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This mismatch results in inaccurate time calculations, causing the guest to perceive hrtimers as firing earlier than expected.

Utilize the TSC_FACTOR from the SEV firmware's secrets page (see "Secrets Page Format" in the SNP Firmware ABI Specification) to calculate the mean TSC frequency, ensuring accurate timekeeping and mitigating clock skew in SEV-SNP VMs.

Use early_ioremap_encrypted() to map the secrets page as ioremap_encrypted() uses kmalloc() which is not available during early TSC initialization and causes a panic.

Detalles técnicos trazas, registros y código del informe original
  [ bp: Drop the silly dummy var:
    https://lore.kernel.org/r/20250630192726.GBaGLlHl84xIopx4Pt@fat_crate.local ]

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).

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2025-38508",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.3,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "LOW"
        },
        "impactScore": 4.7,
        "exploitabilityScore": 2.5
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        "source": "nvd@nist.gov",
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          "defaultStatus": "unaffected"
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        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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          "product": "Linux",
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              "version": "0",
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              "version": "6.15.7",
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              "version": "6.16",
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            "arch/x86/include/asm/sev.h"
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          "defaultStatus": "affected"
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  "published": "2025-08-16T11:15:43.773",
  "references": [
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      "tags": [
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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    {
      "url": "https://git.kernel.org/stable/c/d0195c42e65805938c9eb507657e7cdf8e1e9522",
      "tags": [
        "Patch"
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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  "vulnStatus": "Modified",
  "weaknesses": [
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      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "NVD-CWE-noinfo"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/sev: Use TSC_FACTOR for Secure TSC frequency calculation\n\nWhen using Secure TSC, the GUEST_TSC_FREQ MSR reports a frequency based on\nthe nominal P0 frequency, which deviates slightly (typically ~0.2%) from\nthe actual mean TSC frequency due to clocking parameters.\n\nOver extended VM uptime, this discrepancy accumulates, causing clock skew\nbetween the hypervisor and a SEV-SNP VM, leading to early timer interrupts as\nperceived by the guest.\n\nThe guest kernel relies on the reported nominal frequency for TSC-based\ntimekeeping, while the actual frequency set during SNP_LAUNCH_START may\ndiffer. This mismatch results in inaccurate time calculations, causing the\nguest to perceive hrtimers as firing earlier than expected.\n\nUtilize the TSC_FACTOR from the SEV firmware's secrets page (see \"Secrets\nPage Format\" in the SNP Firmware ABI Specification) to calculate the mean\nTSC frequency, ensuring accurate timekeeping and mitigating clock skew in\nSEV-SNP VMs.\n\nUse early_ioremap_encrypted() to map the secrets page as\nioremap_encrypted() uses kmalloc() which is not available during early TSC\ninitialization and causes a panic.\n\n  [ bp: Drop the silly dummy var:\n    https://lore.kernel.org/r/20250630192726.GBaGLlHl84xIopx4Pt@fat_crate.local ]"
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: x86/sev: Usar TSC_FACTOR para el cálculo de frecuencia de Secure TSC. Al usar Secure TSC, el MSR GUEST_TSC_FREQ informa una frecuencia basada en la frecuencia P0 nominal, que se desvía ligeramente (normalmente ~0,2 %) de la frecuencia media real de TSC debido a los parámetros de reloj. Con el tiempo de actividad prolongado de la máquina virtual, esta discrepancia se acumula, causando un sesgo de reloj entre el hipervisor y una máquina virtual SEV-SNP, lo que lleva a interrupciones tempranas del temporizador según lo percibe el invitado. El kernel invitado se basa en la frecuencia nominal informada para el control de tiempo basado en TSC, mientras que la frecuencia real establecida durante SNP_LAUNCH_START puede diferir. Esta falta de coincidencia resulta en cálculos de tiempo inexactos, lo que hace que el invitado perciba que los temporizadores hr se activan antes de lo esperado. Utilice el factor TSC_FACTOR de la página de secretos del firmware SEV (consulte \"Formato de la página de secretos\" en la especificación ABI del firmware SNP) para calcular la frecuencia media de TSC, lo que garantiza una sincronización precisa y mitiga el desfase de reloj en las máquinas virtuales SEV-SNP. Utilice early_ioremap_encrypted() para mapear la página de secretos, ya que ioremap_encrypted() utiliza kmalloc(), que no está disponible durante la inicialización temprana de TSC y provoca un pánico. [bp: Eliminar la variable ficticia: https://lore.kernel.org/r/20250630192726.GBaGLlHl84xIopx4Pt@fat_crate.local]"
    }
  ],
  "lastModified": "2026-07-30T06:23:23.177",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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}