CVE-2026-90244 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
iommu/dma: Restore locking around msi_page_list
Unlike a group's default domain, which is always freshly allocated and privately owned (iommu_group_alloc_default_domain()), VFIO type1's legacy container merges any newly attached group into an existing domain whenever their iommu_ops and cache-coherency enforcement match.
iommu_dma_get_msi_page() only asserts the caller's own group mutex is held (iommu_group_mutex_assert()). On an IOMMU that publishes IOMMU_RESV_SW_MSI, e.g. ARM SMMU, a VM with two such devices assigned through the legacy container can have their guest drivers probe and allocate MSIs in parallel; each host-side VFIO_DEVICE_SET_IRQS lands on a different device fd and group mutex, but both devices' domains are the same merged domain, so both can enter iommu_dma_get_msi_page() concurrently and corrupt msi_page_list.
commit 288683c92b1a ("iommu: Make iommu_dma_prepare_msi() into a generic operation") dropped the prior msi_prepare_lock on the reasoning that "each iommu_domain is unique to a group," which holds for default domains but not this VFIO type1 case. Restore the static lock, since it's only guarding a corner case and will likely never be contended.
iommufd avoids the equivalent problem by having its own callers (iommufd_sw_map_msi()) take a ctx-wide sw_msi_lock before ever reaching the shared list. VFIO type1 can't mirror that since it dispatches to iommu_dma_sw_msi() which is outside VFIO's jurisdiction.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel contains a concurrency vulnerability within the IOMMU DMA subsystem specifically affecting MSI (Message Signaled Interrupt) page management in legacy container scenarios managed by VFIO type1 drivers. This issue arises from an incorrect assumption regarding domain isolation and locking granularity that was introduced during previous refactoring efforts. The core of the problem lies in how different virtual machine devices interact with shared IOMMU domains when using legacy containers, leading to potential data corruption if not properly synchronized.
In standard configurations, each IOMMU group typically has a default domain that is freshly allocated and privately owned by that specific group through functions like iommu_group_alloc_default_domain. Under these conditions, locking mechanisms tied to individual group mutexes are sufficient because operations on one group do not interfere with another. However, VFIO type1 legacy containers operate differently when merging devices into existing domains. When multiple devices attached via a legacy container share the same IOMMU operational set and cache-coherency enforcement requirements, they may be merged into a single shared domain rather than maintaining separate private domains. This architectural deviation breaks the assumption that group-level mutexes provide exclusive access to all resources within that domain.
The vulnerability manifests in functions such as iommu_dma_get_msi_page(), which previously relied on assertions ensuring the caller held its own group mutex before proceeding with MSI page allocation logic. While this assertion holds true for default domains, it fails when multiple devices from different groups are merged into a common legacy container domain. For instance, on hardware platforms like ARM SMMU that publish IOMMU_RESV_SW_MSI regions, a virtual machine can assign two or more such devices through the same legacy container. Guest drivers probing these devices may trigger parallel MSI allocations in the host kernel environment. Each device corresponds to a distinct file descriptor and group mutex within VFIO, meaning concurrent calls from different guest contexts will pass their respective group-level locks but still target the identical shared domain structure on the host side.
This lack of mutual exclusion at the domain level allows multiple threads to enter critical sections managing the msi_page_list concurrently without proper synchronization relative to each other. The result is a race condition where concurrent modifications to this linked list can lead memory corruption, potentially causing kernel panics or unpredictable behavior in interrupt handling pathways. This specific flaw was inadvertently introduced when commit 288683c92b1a removed the prior msi_prepare_lock under the mistaken belief that each iommu_domain remained unique to its respective group. That reasoning is valid for default domains but does not account for the merged domain scenario inherent in VFIO type1 legacy containers, leaving a critical gap in concurrency control.
The resolution involves restoring a static lock specifically guarding access to the msi_page_list within the IOMMU DMA subsystem. This approach ensures that even when multiple groups share a single underlying domain structure, only one thread can modify the MSI page list at any given time. The chosen implementation utilizes a coarse-grained locking strategy because this specific code path represents an edge case where contention is expected to be rare and transient. By re-introducing global synchronization for this particular resource, the kernel prevents concurrent writes that could corrupt internal data structures while maintaining acceptable performance overhead since the lock protects only a small critical section unlikely to become a bottleneck under normal workloads.
Alternative solutions such as those employed by iommufd demonstrate different architectural approaches to solving similar problems. The iommufd subsystem avoids this class of vulnerability by requiring callers, specifically functions like iommufd_sw_map_msi(), to acquire a context-wide sw_msi lock before accessing shared MSI mapping lists. This design keeps synchronization logic within the VFIO jurisdiction and ensures consistency across all operations managed by that interface. However, legacy VFIO type1 drivers cannot easily adopt this pattern because they dispatch directly to generic IOMMU DMA functions like iommu_dma_sw_msi(), which reside outside the direct control of the VFIO subsystem. Therefore, fixing the issue at the lower-level IOMMU DMA layer is necessary to maintain compatibility and correctness for legacy driver implementations without requiring extensive refactoring of existing device assignment workflows.
From a security classification perspective, this vulnerability aligns with CWE-362, which describes concurrent execution using shared resources with improper synchronization. The lack of proper locking mechanisms allows multiple processes or threads to access critical data structures simultaneously, leading to race conditions that compromise system integrity. In terms of the MITRE ATT&CK framework, while not directly exploitable for remote code execution in most standard configurations, this flaw could potentially be leveraged by a malicious guest VM with assigned devices to cause denial-of-service against the host kernel or other guests sharing the same physical IOMMU hardware through resource corruption and subsequent system instability.
Mitigation strategies primarily involve applying the upstream kernel patch that restores the necessary locking primitives around MSI page list operations. System administrators running affected versions of Linux kernels should ensure their systems are updated to include this fix, particularly if they utilize VFIO passthrough with legacy containers on platforms supporting software-managed MSI regions like ARM SMMU architectures. For environments where immediate patching is not feasible, restricting device assignment to non-legacy container modes or avoiding the configuration of multiple devices sharing merged domains can reduce exposure risk until official updates are deployed. Continuous monitoring for kernel oops messages related to IOMMU subsystems may also help detect potential exploitation attempts in vulnerable deployments.