CVE-2024-26674 x86/lib: Revert to _ASM_EXTABLE_UA() for {get,put}_user() fixups

2024-04-0207:01:39

Linux

github.com

linux kernel

memory error injection

machine check exception

mce

address range check

kernel panic

AI Score

6.9

Confidence

Low

SSVC

Exploitation

none

Automatable

Technical Impact

partial

JSON

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

x86/lib: Revert to _ASM_EXTABLE_UA() for {get,put}_user() fixups

During memory error injection test on kernels >= v6.4, the kernel panics
like below. However, this issue couldn’t be reproduced on kernels <= v6.3.

mce: [Hardware Error]: CPU 296: Machine Check Exception: f Bank 1: bd80000000100134
mce: [Hardware Error]: RIP 10:<ffffffff821b9776> {__get_user_nocheck_4+0x6/0x20}
mce: [Hardware Error]: TSC 411a93533ed ADDR 346a8730040 MISC 86
mce: [Hardware Error]: PROCESSOR 0:a06d0 TIME 1706000767 SOCKET 1 APIC 211 microcode 80001490
mce: [Hardware Error]: Run the above through ‘mcelog --ascii’
mce: [Hardware Error]: Machine check: Data load in unrecoverable area of kernel
Kernel panic - not syncing: Fatal local machine check

The MCA code can recover from an in-kernel #MC if the fixup type is
EX_TYPE_UACCESS, explicitly indicating that the kernel is attempting to
access userspace memory. However, if the fixup type is EX_TYPE_DEFAULT
the only thing that is raised for an in-kernel #MC is a panic.

ex_handler_uaccess() would warn if users gave a non-canonical addresses
(with bit 63 clear) to {get, put}_user(), which was unexpected.

Therefore, commit

b19b74bc99b1 (“x86/mm: Rework address range check in get_user() and put_user()”)

replaced _ASM_EXTABLE_UA() with _ASM_EXTABLE() for {get, put}_user()
fixups. However, the new fixup type EX_TYPE_DEFAULT results in a panic.

Commit

6014bc27561f (“x86-64: make access_ok() independent of LAM”)

added the check gp_fault_address_ok() right before the WARN_ONCE() in
ex_handler_uaccess() to not warn about non-canonical user addresses due
to LAM.

With that in place, revert back to _ASM_EXTABLE_UA() for {get,put}_user()
exception fixups in order to be able to handle in-kernel MCEs correctly
again.

[ bp: Massage commit message. ]

CNA Affected

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "b19b74bc99b1",
        "lessThan": "2aed1b6c33af",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b19b74bc99b1",
        "lessThan": "2da241c5ed78",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b19b74bc99b1",
        "lessThan": "8eed4e00a370",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "arch/x86/lib/getuser.S",
      "arch/x86/lib/putuser.S"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "6.4"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "6.4",
        "versionType": "custom"
      },
      {
        "status": "unaffected",
        "version": "6.6.17",
        "versionType": "custom",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.7.5",
        "versionType": "custom",
        "lessThanOrEqual": "6.7.*"
      },
      {
        "status": "unaffected",
        "version": "6.8",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "arch/x86/lib/getuser.S",
      "arch/x86/lib/putuser.S"
    ],
    "defaultStatus": "affected"
  }
]