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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-40026
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-10-28 10:15:42 UTC
Updated2026-07-30 06:24:06 UTC
DescriptionIn 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>

Risk And Classification

Primary CVSS: v3.1 7.9 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

EPSS: 0.001580000 probability, percentile 0.054920000 (date 2026-07-31)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.9HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H
3.1CNADECLARED7.9HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 a908eca437789589dd4624da428614c1275064dc git Not specified
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 00338255bb1f422642fb2798ebe92e93b6e4209b git Not specified
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 e0ce3ed1048a47986d15aef1a98ebda25560d257 git Not specified
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 ba35a5d775799ce5ad60230be97336f2fefd518e git Not specified
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 3d3abf3f7e8b1abb082070a343de82d7efc80523 git Not specified
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 e7177c7e32cb806f348387b7f4faafd4a5b32054 git Not specified
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 3a062a5c55adc5507600b9ae6d911e247e2f1d6e git Not specified
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 7366830642505683bbe905a2ba5d18d6e4b512b8 git Not specified
CNA Linux Linux affected 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 e750f85391286a4c8100275516973324b621a269 git Not specified
CNA Linux Linux affected 3.0 Not specified
CNA Linux Linux unaffected 3.0 semver Not specified
CNA Linux Linux unaffected 5.4.301 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.246 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.195 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.157 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.111 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.52 6.12.* semver Not specified
CNA Linux Linux unaffected 6.16.12 6.16.* semver Not specified
CNA Linux Linux unaffected 6.17.2 6.17.* semver Not specified
CNA Linux Linux unaffected 6.18 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/e7177c7e32cb806f348387b7f4faafd4a5b32054 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/00338255bb1f422642fb2798ebe92e93b6e4209b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e750f85391286a4c8100275516973324b621a269 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3d3abf3f7e8b1abb082070a343de82d7efc80523 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ba35a5d775799ce5ad60230be97336f2fefd518e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a908eca437789589dd4624da428614c1275064dc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7366830642505683bbe905a2ba5d18d6e4b512b8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e0ce3ed1048a47986d15aef1a98ebda25560d257 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

© CVE.report 2026

Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. It is the responsibility of user to evaluate the accuracy, completeness or usefulness of any information, opinion, advice or other content. EACH USER WILL BE SOLELY RESPONSIBLE FOR ANY consequences of his or her direct or indirect use of this web site. ALL WARRANTIES OF ANY KIND ARE EXPRESSLY DISCLAIMED. This site will NOT BE LIABLE FOR ANY DIRECT, INDIRECT or any other kind of loss.

CVE, CWE, and OVAL are registred trademarks of The MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. This site includes MITRE data granted under the following license.

Free CVE JSON API cve.report/api

CVE.report and Source URL Uptime Status status.cve.report