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CVE-2022-49520

Estado: AnalizadaMedia (5.5)—

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

arm64: compat: Do not treat syscall number as ESR_ELx for a bad syscall

If a compat process tries to execute an unknown system call above the __ARM_NR_COMPAT_END number, the kernel sends a SIGILL signal to the offending process. Information about the error is printed to dmesg in compat_arm_syscall() -> arm64_notify_die() -> arm64_force_sig_fault() -> arm64_show_signal().

arm64_show_signal() interprets a non-zero value for current->thread.fault_code as an exception syndrome and displays the message associated with the ESR_ELx.EC field (bits 31:26). current->thread.fault_code is set in compat_arm_syscall() -> arm64_notify_die() with the bad syscall number instead of a valid ESR_ELx value.

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This means that the ESR_ELx.EC field has the value that the user set for the syscall number and the kernel can end up printing bogus exception messages*. For example, for the syscall number 0x68000000, which evaluates to ESR_ELx.EC value of 0x1A (ESR_ELx_EC_FPAC) the kernel prints this error:

which is misleading, as the bad compat syscall has nothing to do with pointer authentication.

Stop arm64_show_signal() from printing exception syndrome information by having compat_arm_syscall() set the ESR_ELx value to 0, as it has no meaning for an invalid system call number. The example above now becomes:

which although shows less information because the syscall number, wrongfully advertised as the ESR value, is missing, it is better than showing plainly wrong information. The syscall number can be easily obtained with strace.

*A 32-bit value above or equal to 0x8000_0000 is interpreted as a negative integer in compat_arm_syscal() and the condition scno < __ARM_NR_COMPAT_END evaluates to true; the syscall will exit to userspace in this case with the ENOSYS error code instead of arm64_notify_die() being called.

Detalles técnicos trazas, registros y código del informe original
[   18.349161] syscall[300]: unhandled exception: ERET/ERETAA/ERETAB, ESR 0x68000000, Oops - bad compat syscall(2) in syscall[10000+50000]
[   18.350639] CPU: 2 PID: 300 Comm: syscall Not tainted 5.18.0-rc1 #79
[   18.351249] Hardware name: Pine64 RockPro64 v2.0 (DT)
[..]

[   19.935275] syscall[301]: unhandled exception: Oops - bad compat syscall(2) in syscall[10000+50000]
[   19.936124] CPU: 1 PID: 301 Comm: syscall Not tainted 5.18.0-rc1-00005-g7e08006d4102 #80
[   19.936894] Hardware name: Pine64 RockPro64 v2.0 (DT)
[..]

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-2022-49520",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 5.5,
          "attackVector": "LOCAL",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 1.8
      }
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          "programFiles": [
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  "published": "2025-02-26T07:01:28.017",
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  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "NVD-CWE-noinfo"
        }
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  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\narm64: compat: Do not treat syscall number as ESR_ELx for a bad syscall\n\nIf a compat process tries to execute an unknown system call above the\n__ARM_NR_COMPAT_END number, the kernel sends a SIGILL signal to the\noffending process. Information about the error is printed to dmesg in\ncompat_arm_syscall() -> arm64_notify_die() -> arm64_force_sig_fault() ->\narm64_show_signal().\n\narm64_show_signal() interprets a non-zero value for\ncurrent->thread.fault_code as an exception syndrome and displays the\nmessage associated with the ESR_ELx.EC field (bits 31:26).\ncurrent->thread.fault_code is set in compat_arm_syscall() ->\narm64_notify_die() with the bad syscall number instead of a valid ESR_ELx\nvalue. This means that the ESR_ELx.EC field has the value that the user set\nfor the syscall number and the kernel can end up printing bogus exception\nmessages*. For example, for the syscall number 0x68000000, which evaluates\nto ESR_ELx.EC value of 0x1A (ESR_ELx_EC_FPAC) the kernel prints this error:\n\n[   18.349161] syscall[300]: unhandled exception: ERET/ERETAA/ERETAB, ESR 0x68000000, Oops - bad compat syscall(2) in syscall[10000+50000]\n[   18.350639] CPU: 2 PID: 300 Comm: syscall Not tainted 5.18.0-rc1 #79\n[   18.351249] Hardware name: Pine64 RockPro64 v2.0 (DT)\n[..]\n\nwhich is misleading, as the bad compat syscall has nothing to do with\npointer authentication.\n\nStop arm64_show_signal() from printing exception syndrome information by\nhaving compat_arm_syscall() set the ESR_ELx value to 0, as it has no\nmeaning for an invalid system call number. The example above now becomes:\n\n[   19.935275] syscall[301]: unhandled exception: Oops - bad compat syscall(2) in syscall[10000+50000]\n[   19.936124] CPU: 1 PID: 301 Comm: syscall Not tainted 5.18.0-rc1-00005-g7e08006d4102 #80\n[   19.936894] Hardware name: Pine64 RockPro64 v2.0 (DT)\n[..]\n\nwhich although shows less information because the syscall number,\nwrongfully advertised as the ESR value, is missing, it is better than\nshowing plainly wrong information. The syscall number can be easily\nobtained with strace.\n\n*A 32-bit value above or equal to 0x8000_0000 is interpreted as a negative\ninteger in compat_arm_syscal() and the condition scno < __ARM_NR_COMPAT_END\nevaluates to true; the syscall will exit to userspace in this case with the\nENOSYS error code instead of arm64_notify_die() being called."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: arm64: compat: No trate el número de llamada al sistema como ESR_ELx para una llamada al sistema incorrecta Si un proceso compat intenta ejecutar una llamada al sistema desconocida por encima del número __ARM_NR_COMPAT_END, el kernel envía una señal SIGILL al proceso infractor. La información sobre el error se imprime en dmesg en compat_arm_syscall() -&gt; arm64_notify_die() -&gt; arm64_force_sig_fault() -&gt; arm64_show_signal(). arm64_show_signal() interpreta un valor distinto de cero para current-&gt;thread.fault_code como un síndrome de excepción y muestra el mensaje asociado con el campo ESR_ELx.EC (bits 31:26). current-&gt;thread.fault_code se configura en compat_arm_syscall() -&gt; arm64_notify_die() con el número de llamada al sistema incorrecto en lugar de un valor ESR_ELx válido. Esto significa que el campo ESR_ELx.EC tiene el valor que el usuario configuró para el número de llamada al sistema y el núcleo puede terminar imprimiendo mensajes de excepción falsos*. Por ejemplo, para el número de llamada al sistema 0x68000000, que evalúa al valor ESR_ELx.EC 0x1A (ESR_ELx_EC_FPAC), el núcleo imprime este error: [ 18.349161] syscall[300]: excepción no controlada: ERET/ERETAA/ERETAB, ESR 0x68000000, Oops - mala compatibilidad syscall(2) en syscall[10000+50000] [ 18.350639] CPU: 2 PID: 300 Comm: syscall No contaminado 5.18.0-rc1 #79 [ 18.351249] Nombre del hardware: Pine64 RockPro64 v2.0 (DT) [..] lo cual es engañoso, ya que la llamada al sistema de compatibilidad incorrecta no tiene nada que ver con la autenticación de puntero. Evite que arm64_show_signal() imprima información sobre el síndrome de excepción haciendo que compat_arm_syscall() establezca el valor ESR_ELx en 0, ya que no tiene significado para un número de llamada de sistema no válido. El ejemplo anterior ahora se convierte en: [ 19.935275] syscall[301]: excepción no controlada: Oops - bad compat syscall(2) in syscall[10000+50000] [ 19.936124] CPU: 1 PID: 301 Comm: syscall Not tainted 5.18.0-rc1-00005-g7e08006d4102 #80 [ 19.936894] Nombre del hardware: Pine64 RockPro64 v2.0 (DT) [..] que aunque muestra menos información porque falta el número de syscall, anunciado erróneamente como el valor ESR, es mejor que mostrar información claramente errónea. El número de syscall se puede obtener fácilmente con strace. *Un valor de 32 bits mayor o igual a 0x8000_0000 se interpreta como un entero negativo en compat_arm_syscal() y la condición scno &lt; __ARM_NR_COMPAT_END se evalúa como verdadera; la llamada al sistema saldrá al espacio de usuario en este caso con el código de error ENOSYS en lugar de llamar a arm64_notify_die()."
    }
  ],
  "lastModified": "2026-08-15T13:17:23.770",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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}