CVE-2025-40026High· 7.9▾ TwilightIn 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…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 43.5 · likelihood 0 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake. The CVSS score shown above comes from the assigning CNA record, not NVD.
Exploit-prediction probability, daily snapshots since Oct 15.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
Last analysed / modified upstream
0.2%
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>
Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < a908eca437789589dd4624da428614c1275064dcLinux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < 00338255bb1f422642fb2798ebe92e93b6e4209bLinux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < e0ce3ed1048a47986d15aef1a98ebda25560d257Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < ba35a5d775799ce5ad60230be97336f2fefd518eLinux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < 3d3abf3f7e8b1abb082070a343de82d7efc80523Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < e7177c7e32cb806f348387b7f4faafd4a5b32054Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < 3a062a5c55adc5507600b9ae6d911e247e2f1d6eLinux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < 7366830642505683bbe905a2ba5d18d6e4b512b8Linux >= 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 < e750f85391286a4c8100275516973324b621a269Linux 3.0Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
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