---
id: CVE-2025-40026
title: 'KVM: x86: Don''t (re)check L1 intercepts when completing userspace I/O'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O

  When completing emulation of instruction that generated a userspace exit
  for I/O, don't recheck L…
severity: high
cvss: 7.9
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    a908eca437789589dd4624da428614c1275064dc
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    00338255bb1f422642fb2798ebe92e93b6e4209b
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    e0ce3ed1048a47986d15aef1a98ebda25560d257
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    ba35a5d775799ce5ad60230be97336f2fefd518e
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    3d3abf3f7e8b1abb082070a343de82d7efc80523
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    e7177c7e32cb806f348387b7f4faafd4a5b32054
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    3a062a5c55adc5507600b9ae6d911e247e2f1d6e
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    7366830642505683bbe905a2ba5d18d6e4b512b8
  - >-
    Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 <
    e750f85391286a4c8100275516973324b621a269
  - Linux 3.0
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-15T21:56:14.274469Z'
published: '2025-10-28'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T22:02:36.361Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-40026'
references:
  - url: 'https://git.kernel.org/stable/c/a908eca437789589dd4624da428614c1275064dc'
  - url: 'https://git.kernel.org/stable/c/00338255bb1f422642fb2798ebe92e93b6e4209b'
  - url: 'https://git.kernel.org/stable/c/e0ce3ed1048a47986d15aef1a98ebda25560d257'
  - url: 'https://git.kernel.org/stable/c/ba35a5d775799ce5ad60230be97336f2fefd518e'
  - url: 'https://git.kernel.org/stable/c/3d3abf3f7e8b1abb082070a343de82d7efc80523'
  - url: 'https://git.kernel.org/stable/c/e7177c7e32cb806f348387b7f4faafd4a5b32054'
  - url: 'https://git.kernel.org/stable/c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e'
  - url: 'https://git.kernel.org/stable/c/7366830642505683bbe905a2ba5d18d6e4b512b8'
  - url: 'https://git.kernel.org/stable/c/e750f85391286a4c8100275516973324b621a269'
tags:
  - cve.org
epss: 0.0017
epssPercentile: 0.06411
ingestedAt: '2026-10-15T22:48:25.537Z'
---

## Overview

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

KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O

When completing emulation of instruction that generated a userspace exit
for I/O, don't recheck L1 intercepts as KVM has already finished that
phase of instruction execution, i.e. has already committed to allowing L2
to perform I/O.  If L1 (or host userspace) modifies the I/O permission
bitmaps during the exit to userspace,  KVM will treat the access as being
intercepted despite already having emulated the I/O access.

Pivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation.
Of the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the
intended "recipient") can reach the code in question.  gp_interception()'s
use is mutually exclusive with is_guest_mode(), and
complete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with
EMULTYPE_SKIP.

The bad behavior was detected by a syzkaller program that toggles port I/O
interception during the userspace I/O exit, ultimately resulting in a WARN
on vcpu->arch.pio.count being non-zero due to KVM no completing emulation
of the I/O instruction.

  WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm]
  Modules linked in: kvm_intel kvm irqbypass
  CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm]
  PKRU: 55555554
  Call Trace:
   <TASK>
   kvm_fast_pio+0xd6/0x1d0 [kvm]
   vmx_handle_exit+0x149/0x610 [kvm_intel]
   kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm]
   kvm_vcpu_ioctl+0x244/0x8c0 [kvm]
   __x64_sys_ioctl+0x8a/0xd0
   do_syscall_64+0x5d/0xc60
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
   </TASK>

## Affected

- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < a908eca437789589dd4624da428614c1275064dc`
- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < 00338255bb1f422642fb2798ebe92e93b6e4209b`
- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < e0ce3ed1048a47986d15aef1a98ebda25560d257`
- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < ba35a5d775799ce5ad60230be97336f2fefd518e`
- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < 3d3abf3f7e8b1abb082070a343de82d7efc80523`
- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < e7177c7e32cb806f348387b7f4faafd4a5b32054`
- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < 3a062a5c55adc5507600b9ae6d911e247e2f1d6e`
- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < 7366830642505683bbe905a2ba5d18d6e4b512b8`
- `Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < e750f85391286a4c8100275516973324b621a269`
- `Linux 3.0`

## Remediation

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