CVE-2021-46990

2024-02-2809:15:37

Linux

web.nvd.nist.gov

4081

cve

2021

46990

linux kernel

vulnerability

powerpc/64s

entry flush barrier

debugging

crash mitigation

security fix

AI Score

6.3

Confidence

Low

EPSS

Percentile

13.0%

JSON

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

powerpc/64s: Fix crashes when toggling entry flush barrier

The entry flush mitigation can be enabled/disabled at runtime via a
debugfs file (entry_flush), which causes the kernel to patch itself to
enable/disable the relevant mitigations.

However depending on which mitigation we’re using, it may not be safe to
do that patching while other CPUs are active. For example the following
crash:

sleeper[15639]: segfault (11) at c000000000004c20 nip c000000000004c20 lr c000000000004c20

Shows that we returned to userspace with a corrupted LR that points into
the kernel, due to executing the partially patched call to the fallback
entry flush (ie. we missed the LR restore).

Fix it by doing the patching under stop machine. The CPUs that aren’t
doing the patching will be spinning in the core of the stop machine
logic. That is currently sufficient for our purposes, because none of
the patching we do is to that code or anywhere in the vicinity.

Affected configurations

Vulners

Node

linuxlinux_kernelRange5.10–4.4.269

linuxlinux_kernelRange4.5.0–4.9.269

linuxlinux_kernelRange4.10.0–4.14.233

linuxlinux_kernelRange4.15.0–4.19.191

linuxlinux_kernelRange4.20.0–5.4.120

linuxlinux_kernelRange5.5.0–5.10.38

linuxlinux_kernelRange5.11.0–5.11.22

linuxlinux_kernelRange5.12.0–5.12.5

linuxlinux_kernelRange5.13.0≥

VendorProductVersionCPE
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

Vendor	Product	Version	CPE
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "arch/powerpc/lib/feature-fixups.c"
    ],
    "versions": [
      {
        "version": "4a1e90af718d",
        "lessThan": "8382b15864e5",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "fa4bf9f38184",
        "lessThan": "0c25a7bb697f",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "db01cad9efe3",
        "lessThan": "ee4b7aab93c2",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "f69bb4e51f41",
        "lessThan": "2db22ba4e0e1",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "b65458b6be80",
        "lessThan": "0b4eb172cc12",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "f79643787e0a",
        "lessThan": "d2e3590ca39c",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "f79643787e0a",
        "lessThan": "dd0d6117052f",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "f79643787e0a",
        "lessThan": "5bc00fdda1e9",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "f79643787e0a",
        "lessThan": "aec86b052df6",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "arch/powerpc/lib/feature-fixups.c"
    ],
    "versions": [
      {
        "version": "5.10",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "5.10",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.4.269",
        "lessThanOrEqual": "4.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.9.269",
        "lessThanOrEqual": "4.9.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.14.233",
        "lessThanOrEqual": "4.14.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.19.191",
        "lessThanOrEqual": "4.19.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.4.120",
        "lessThanOrEqual": "5.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.38",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.11.22",
        "lessThanOrEqual": "5.11.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.12.5",
        "lessThanOrEqual": "5.12.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.13",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]