CVE-2025-38351 KVM: x86/hyper-v: Skip non-canonical addresses during PV TLB flush
A malicious guest can trigger a kernel warning and potential denial of service by passing non-canonical addresses to Hyper-V TLB flush hypercalls on Intel systems.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-38351?
CVE-2025-38351 is a medium-severity denial of service vulnerability in Linux kernel, published on 19 Jul 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
KVM: x86/hyper-v: Skip non-canonical addresses during PV TLB flush
In KVM guests with Hyper-V hypercalls enabled, the hypercalls HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST and HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX allow a guest to request invalidation of portions of a virtual TLB. For this, the hypercall parameter includes a list of GVAs that are supposed to be invalidated.
However, when non-canonical GVAs are passed, there is currently no filtering in place and they are eventually passed to checked invocations of INVVPID on Intel / INVLPGA on AMD. While AMD's INVLPGA silently ignores non-canonical addresses (effectively a no-op), Intel's INVVPID explicitly signals VM-Fail and ultimately triggers the WARN_ONCE in invvpid_error():
invvpid failed: ext=0x0 vpid=1 gva=0xaaaaaaaaaaaaa000 WARNING: CPU: 6 PID: 326 at arch/x86/kvm/vmx/vmx.c:482 invvpid_error+0x91/0xa0 [kvm_intel] Modules linked in: kvm_intel kvm 9pnet_virtio irqbypass fuse CPU: 6 UID: 0 PID: 326 Comm: kvm-vm Not tainted 6.15.0 #14 PREEMPT(voluntary) RIP: 0010:invvpid_error+0x91/0xa0 [kvm_intel] Call Trace: vmx_flush_tlb_gva+0x320/0x490 [kvm_intel] kvm_hv_vcpu_flush_tlb+0x24f/0x4f0 [kvm] kvm_arch_vcpu_ioctl_run+0x3013/0x5810 [kvm]
Hyper-V documents that invalid GVAs (those that are beyond a partition's GVA space) are to be ignored. While not completely clear whether this ruling also applies to non-canonical GVAs, it is likely fine to make that assumption, and manual testing on Azure confirms "real" Hyper-V interprets the specification in the same way.
Skip non-canonical GVAs when processing the list of address to avoid tripping the INVVPID failure. Alternatively, KVM could filter out "bad" GVAs before inserting into the FIFO, but practically speaking the only downside of pushing validation to the final processing is that doing so is suboptimal for the guest, and no well-behaved guest will request TLB flushes for non-canonical addresses.
Which versions are affected by CVE-2025-38351?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-38351?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-38351 being exploited?
There is no known exploitation of CVE-2025-38351 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-38351, DEBIAN-CVE-2025-38351, GHSA-x77v-68j6-p42v, ROOT-OS-UBUNTU-2404-CVE-2025-38351, UBUNTU-CVE-2025-38351.