CVE-2021-47429 powerpc/64s: Fix unrecoverable MCE calling async handler from NMI

2024-05-2115:04:14

Linux

github.com

linux kernel

vulnerability resolved

powerpc/64s

machine check handler

nmi handler

unrecoverable mce

AI Score

6.8

Confidence

Low

EPSS

Percentile

9.0%

SSVC

Exploitation

none

Automatable

Technical Impact

partial

JSON

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

powerpc/64s: Fix unrecoverable MCE calling async handler from NMI

The machine check handler is not considered NMI on 64s. The early
handler is the true NMI handler, and then it schedules the
machine_check_exception handler to run when interrupts are enabled.

This works fine except the case of an unrecoverable MCE, where the true
NMI is taken when MSR[RI] is clear, it can not recover, so it calls
machine_check_exception directly so something might be done about it.

Calling an async handler from NMI context can result in irq state and
other things getting corrupted. This can also trigger the BUG at
arch/powerpc/include/asm/interrupt.h:168
BUG_ON(!arch_irq_disabled_regs(regs) && !(regs->msr & MSR_EE));

Fix this by making an _async version of the handler which is called
in the normal case, and a NMI version that is called for unrecoverable
interrupts.

CNA Affected

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "2b43dd7653cc",
        "lessThan": "d7a8e38999fb",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "2b43dd7653cc",
        "lessThan": "f08fb25bc669",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "arch/powerpc/include/asm/interrupt.h",
      "arch/powerpc/kernel/exceptions-64s.S",
      "arch/powerpc/kernel/traps.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "5.14"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "5.14",
        "versionType": "custom"
      },
      {
        "status": "unaffected",
        "version": "5.14.12",
        "versionType": "custom",
        "lessThanOrEqual": "5.14.*"
      },
      {
        "status": "unaffected",
        "version": "5.15",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "arch/powerpc/include/asm/interrupt.h",
      "arch/powerpc/kernel/exceptions-64s.S",
      "arch/powerpc/kernel/traps.c"
    ],
    "defaultStatus": "affected"
  }
]