CVE-2024-26706 parisc: Fix random data corruption from exception handler

2024-04-0314:55:09

Linux

www.cve.org

linux kernel

exception handler

data corruption

bug fix

compiler

fault handler

7.9 High

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

15.5%

JSON

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

parisc: Fix random data corruption from exception handler

The current exception handler implementation, which assists when accessing
user space memory, may exhibit random data corruption if the compiler decides
to use a different register than the specified register %r29 (defined in
ASM_EXCEPTIONTABLE_REG) for the error code. If the compiler choose another
register, the fault handler will nevertheless store -EFAULT into %r29 and thus
trash whatever this register is used for.
Looking at the assembly I found that this happens sometimes in emulate_ldd().

To solve the issue, the easiest solution would be if it somehow is
possible to tell the fault handler which register is used to hold the error
code. Using %0 or %1 in the inline assembly is not posssible as it will show
up as e.g. %r29 (with the “%r” prefix), which the GNU assembler can not
convert to an integer.

This patch takes another, better and more flexible approach:
We extend the __ex_table (which is out of the execution path) by one 32-word.
In this word we tell the compiler to insert the assembler instruction
“or %r0,%r0,%reg”, where %reg references the register which the compiler
choosed for the error return code.
In case of an access failure, the fault handler finds the __ex_table entry and
can examine the opcode. The used register is encoded in the lowest 5 bits, and
the fault handler can then store -EFAULT into this register.

Since we extend the __ex_table to 3 words we can’t use the BUILDTIME_TABLE_SORT
config option any longer.

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "arch/parisc/Kconfig",
      "arch/parisc/include/asm/assembly.h",
      "arch/parisc/include/asm/extable.h",
      "arch/parisc/include/asm/special_insns.h",
      "arch/parisc/include/asm/uaccess.h",
      "arch/parisc/kernel/cache.c",
      "arch/parisc/kernel/unaligned.c",
      "arch/parisc/mm/fault.c"
    ],
    "versions": [
      {
        "version": "1da177e4c3f4",
        "lessThan": "23027309b099",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1da177e4c3f4",
        "lessThan": "fa69a8063f8b",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1da177e4c3f4",
        "lessThan": "ce31d79aa1f1",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1da177e4c3f4",
        "lessThan": "8b1d72395635",
        "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/parisc/Kconfig",
      "arch/parisc/include/asm/assembly.h",
      "arch/parisc/include/asm/extable.h",
      "arch/parisc/include/asm/special_insns.h",
      "arch/parisc/include/asm/uaccess.h",
      "arch/parisc/kernel/cache.c",
      "arch/parisc/kernel/unaligned.c",
      "arch/parisc/mm/fault.c"
    ],
    "versions": [
      {
        "version": "6.1.79",
        "lessThanOrEqual": "6.1.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.6.18",
        "lessThanOrEqual": "6.6.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.7.6",
        "lessThanOrEqual": "6.7.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.8",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]