CVE-2026-80895
Low risk· EPSS 6%Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel's mshv module, a race condition exists between publishing a VP pointer in pt_vp_array and the irqfd fast assertion path. On weakly-ordered architectures, a reader may observe a non-NULL pointer before the VP struct is fully initialized, leading to use of partially initialized fields.
Risk Assessment
The risk involves potential use of incorrect data in the interrupt path, which could lead to unpredictable system behavior, crashes, or privilege escalation in environments using mshv. However, the attack requires local access and the ability to register an irqfd for a not-yet-created VP.
Recommendation
Apply the official Linux kernel patch that introduces memory barriers (smp_store_release/smp_load_acquire) in the relevant locations. Update the system to a kernel version containing the fix.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: mshv: Order pt_vp_array publish against irqfd assertion path mshv_partition_ioctl_create_vp() initialises a VP struct (allocations, mutex_init, init_waitqueue_head, page mappings) and then publishes the pointer into partition->pt_vp_array. Several ISR paths read this array locklessly: the intercept ISR, the two scheduler ISRs, and mshv_try_assert_irq_fast() on the irqfd fast path. Of these, only mshv_try_assert_irq_fast() can structurally race the publish. It runs from an eventfd waker without holding pt_mutex, and MSHV_IRQFD does not require the target lapic_apic_id (== vp_index) to refer to an existing VP at registration time. A user can therefore register an irqfd targeting a yet-to-be-created VP, then trigger mshv_try_assert_irq_fast() concurrently with MSHV_CREATE_VP for the same index. On weakly-ordered architectures the reader can observe a non-NULL pointer in pt_vp_array before the initialising stores to the VP struct become visible, leading to use of partially-initialised fields (e.g. vp_register_page). The other ISR readers cannot reach this race: the hypervisor will not generate intercept or scheduler messages for a VP that has never been told to run, and the user can only call MSHV_RUN_VP on the VP fd returned by MSHV_CREATE_VP, which by construction is returned after the publish. Leave those readers as plain loads. Use smp_store_release() in mshv_partition_ioctl_create_vp() to publish the pointer, and pair it with smp_load_acquire() in mshv_try_assert_irq_fast(). On x86 these compile to plain accesses under TSO; on ARM64 they emit one-instruction acquire/release barriers, acceptable on this fast path. The destroy-side path (destroy_partition() clearing pt_vp_array[i] to NULL after kfree(vp)) has a separate ordering and lifetime concern that is out of scope here.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS