CVE-2026-98465 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
RISC-V: KVM: Serialize IMSIC attributes with vCPU migration
KVM device ioctls are not serialized against KVM_RUN. As a result, kvm_riscv_aia_imsic_rw_attr() can snapshot the physical CPU and HGEI of an IMSIC VS-file before a concurrent vCPU migration releases it.
The HGEI can then be allocated to another vCPU before imsic_vsfile_rw() uses the stale tuple. A GET or SET attribute may consequently access the new owner's interrupt file.
Serialize the entire IMSIC attribute operation with the target vCPU mutex. This prevents the VS-file from being migrated and recycled until the attribute access completes. Acquire the mutex killably so that the device ioctl remains interruptible while waiting for KVM_RUN to finish.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel's Kernel-based Virtual Machine (KVM) subsystem, specifically within the RISC-V architecture implementation, contained a critical concurrency flaw related to the serialization of Interrupt Management State Unit (IMSIC) attributes during virtual Central Processing Unit (vCPU) migration operations. This vulnerability stems from an insufficient synchronization mechanism when handling device ioctls that interact with IMSIC Virtual System File descriptors. The core issue lies in the lack of atomicity between attribute read or write operations and the lifecycle management of vCPUs, particularly regarding the release and reallocation of physical resources associated with interrupt routing.
The technical flaw manifests through a race condition where kvm_riscv_aia_imsic_rw_attr() captures state information, such as the physical CPU identifier and Host Guest External Interrupt (HGEI) vector, from an IMSIC VS-file before a concurrent vCPU migration completes its release of that resource. Because KVM device ioctls were not serialized against the execution context of kvm_riscv_aia_imsic_rw_attr(), there exists a window where the physical CPU and HGEI data become stale relative to the actual ownership status of the VS-file. During this interval, the underlying infrastructure may deallocate or repurpose these resources for another vCPU that has been scheduled onto the same physical hardware.
This race condition leads to a severe security implication classified under CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). When an attacker-controlled guest attempts to GET or SET IMSIC attributes, it may inadvertently access interrupt files belonging to a different vCPU that has inherited the recycled physical resources. This cross-vCPU interference violates isolation boundaries enforced by the hypervisor, potentially allowing one virtual machine to observe or manipulate interrupt states intended for another. In worst-case scenarios, this could lead to information disclosure of sensitive guest state data or denial of service through improper interrupt delivery and masking within the affected VMs.
The operational impact is significant as it undermines the fundamental security guarantees provided by hardware-assisted virtualization on RISC-V platforms. By allowing attribute operations to proceed without ensuring exclusive access to the target vCPU's migration mutex, the kernel permits state corruption that can destabilize guest operating systems or expose internal hypervisor structures. The vulnerability highlights a gap in handling shared mutable state during dynamic resource reallocation events typical of live migration and load balancing scenarios within virtualized environments.
To mitigate this issue, the fix implements strict serialization by acquiring the target vCPU mutex for the entirety of the IMSIC attribute operation. This ensures that the VS-file cannot be migrated or recycled while an attribute access is in progress, thereby maintaining data consistency between the snapshotted physical CPU/HGEI tuple and its actual ownership status. Furthermore, the implementation acquires this mutex killably, which allows device ioctls to remain interruptible if they wait for kvm_riscv_aia_imsic_rw_attr() to finish. This design choice prevents potential deadlocks or system hangs while still enforcing the necessary mutual exclusion during critical sections of interrupt management state modification.
From a threat modeling perspective aligned with MITRE ATT&CK, this vulnerability relates to techniques involving resource sharing and race conditions that can be exploited for privilege escalation within virtualized environments or lateral movement between VMs if isolation is compromised. Security practitioners should ensure their RISC-V based KVM deployments are updated with patches addressing this serialization gap. Regular auditing of hypervisor configurations and monitoring for unusual interrupt patterns across vCPUs on shared physical cores can serve as additional defensive measures against exploitation attempts targeting similar concurrency flaws in virtualization stacks.