---
id: CVE-2026-89751
title: 'x86/tdx: Fix off-by-one in port I/O handling'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  x86/tdx: Fix off-by-one in port I/O handling

  handle_in() and handle_out() in arch/x86/coco/tdx/tdx.c use:

      u64 mask = GENMASK(BITS_PER_BYTE * size, 0);

  GENMASK(h,…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cvssSource: vendor
cwe:
  - CWE-193
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 03149948832a078f759022ed5b92e722d8d23c26 <
    c6875423ad849ac234ab9812eb72f37ff8a490b4
  - >-
    Linux >= 03149948832a078f759022ed5b92e722d8d23c26 <
    220011fe95fc78b2bc2d7d43893bc73957a5c811
  - >-
    Linux >= 03149948832a078f759022ed5b92e722d8d23c26 <
    222b7005e4519f633b4cd666226256abbab46a1a
  - >-
    Linux >= 03149948832a078f759022ed5b92e722d8d23c26 <
    c4a22154870813d10aa0b4c734a574c726f9d4b0
  - >-
    Linux >= 03149948832a078f759022ed5b92e722d8d23c26 <
    bb45f705c4440dd3c689328319b88dd28770bbb8
  - >-
    Linux >= 03149948832a078f759022ed5b92e722d8d23c26 <
    0f63e656b1c679d32ac595de29d10c03efca6a25
  - Linux 5.19
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:52:05.025Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89751'
references:
  - url: 'https://git.kernel.org/stable/c/c6875423ad849ac234ab9812eb72f37ff8a490b4'
  - url: 'https://git.kernel.org/stable/c/220011fe95fc78b2bc2d7d43893bc73957a5c811'
  - url: 'https://git.kernel.org/stable/c/222b7005e4519f633b4cd666226256abbab46a1a'
  - url: 'https://git.kernel.org/stable/c/c4a22154870813d10aa0b4c734a574c726f9d4b0'
  - url: 'https://git.kernel.org/stable/c/bb45f705c4440dd3c689328319b88dd28770bbb8'
  - url: 'https://git.kernel.org/stable/c/0f63e656b1c679d32ac595de29d10c03efca6a25'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89751.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89751'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532152'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89751'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89751'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89751.mbox
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.00173
epssPercentile: 0.06648
ingestedAt: '2026-09-14T15:23:07.448Z'
---

## Overview

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

x86/tdx: Fix off-by-one in port I/O handling

handle_in() and handle_out() in arch/x86/coco/tdx/tdx.c use:

    u64 mask = GENMASK(BITS_PER_BYTE * size, 0);

GENMASK(h, l) includes bit h. For size=1 (INB), this produces
GENMASK(8, 0) = 0x1FF (9 bits) instead of GENMASK(7, 0) = 0xFF (8
bits). The mask is one bit too wide for all I/O sizes.

Fix the mask calculation.

## Affected

- `Linux >= 03149948832a078f759022ed5b92e722d8d23c26 < c6875423ad849ac234ab9812eb72f37ff8a490b4`
- `Linux >= 03149948832a078f759022ed5b92e722d8d23c26 < 220011fe95fc78b2bc2d7d43893bc73957a5c811`
- `Linux >= 03149948832a078f759022ed5b92e722d8d23c26 < 222b7005e4519f633b4cd666226256abbab46a1a`
- `Linux >= 03149948832a078f759022ed5b92e722d8d23c26 < c4a22154870813d10aa0b4c734a574c726f9d4b0`
- `Linux >= 03149948832a078f759022ed5b92e722d8d23c26 < bb45f705c4440dd3c689328319b88dd28770bbb8`
- `Linux >= 03149948832a078f759022ed5b92e722d8d23c26 < 0f63e656b1c679d32ac595de29d10c03efca6a25`
- `Linux 5.19`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89751.json)