CVE-2025-40026
- Published: 1761646542
- Last modified: 1761747352
CVE-2025-40026 — 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…
Related CVE by CWE
No related CWE found.
Top CVE for Vendor
No vendor taxonomy on this entry.
Recently Exploited Similar Vulnerabilities
No recent KEV-listed items for this vendor/product.
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:
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
🧠 Explainer: What this vulnerability means
Summary: The issue in the product by the vendor (CWE: unspecified) may enable attacks.
Impact: Attackers could gain unauthorized access, execute code, or disrupt services.
Mitigation: Apply the latest vendor patch or update to a fixed version; disable vulnerable modules where possible.
No vendor/product data yet.
No explicit mitigation/advisory links found in references.