CVE-2026-98466 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
KVM: arm64: Transfer the hyp stack pages out of the host stage-2
fix_host_ownership() walks only the linear-map alias of each memblock region, and the per-CPU hyp stack, mapped in the private VA range for its guard page, has none.
Walk each stack's VA range with the same walker.
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Analysis
by VulDB Data Team • 10/18/2026
The vulnerability described relates to a specific implementation flaw within the KVM ARM64 subsystem of the Linux kernel, specifically concerning how memory ownership and stage-2 address translation are managed for hypervisor stacks. In virtualization environments using ARM architecture, the host operating system manages physical memory through a first-stage page table while the Virtual Machine Monitor (KVM) maintains second-stage page tables to map guest-visible addresses to actual physical frames. A critical aspect of this process involves ensuring that certain kernel structures, particularly those used by the hypervisor itself during execution in EL2 exception level, are correctly excluded from or handled within these translation domains to prevent security breaches and system instability. The function fix_host_ownership is responsible for walking through memory regions to adjust ownership attributes, typically targeting the linear-map alias which covers most of kernel space but fails to account for all critical per-CPU data structures.
The core technical flaw lies in the scope of the virtual address range traversal performed by fix_host_ownership. This function iterates over memblock regions using a walker that targets only the linear-map alias, assuming this coverage is sufficient for identifying and adjusting host-owned memory pages within the stage-2 translation context. However, the per-CPU hypervisor stack, which resides in a private virtual address range specifically allocated to provide guard page protection against stack overflow attacks, falls outside the bounds of the linear map. Consequently, when fix_host_ownership executes its traversal logic, it completely bypasses these hyp stack pages because they are not part of the linear-map alias structure being scanned. This oversight means that the necessary ownership transfers or attribute adjustments for these specific memory regions are never applied during critical initialization or state transition phases involving stage-2 page table management.
The operational impact of this omission is significant, particularly in scenarios where KVM transitions between different execution states or when managing nested virtualization contexts on ARM64 platforms. Without the correct ownership transfer for hyp stack pages, there exists a risk that these memory regions might remain incorrectly attributed to guest-owned stage-2 mappings or fail to be properly isolated from host-visible translations. This can lead to potential information disclosure if guest code gains access to sensitive hypervisor state stored in those stacks, or it may result in system crashes due to invalid memory accesses when the hypervisor attempts to utilize stack pages that are not correctly mapped under its own protection domain. Furthermore, such misconfigurations undermine the integrity of the isolation boundary between host and guest environments, potentially allowing a malicious virtual machine to interfere with hypervisor operations through side-channel attacks or direct memory corruption if the guard page protections are compromised by incorrect mapping attributes.
From a standards perspective, this vulnerability aligns closely with CWE-20 Improper Input Validation as it involves failing to validate that all relevant memory regions belonging to the host are correctly processed during ownership transitions. It also relates to CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer because the linear-map walker fails to encompass the full extent of required kernel structures, leading to out-of-bounds logical access where critical data is ignored. In terms of MITRE ATT&CK mapping for virtualization environments, this flaw could be exploited in conjunction with techniques such as T1059 Command and Scripting Interpreter if an attacker leverages guest-side execution to trigger specific KVM state changes that expose the misconfigured hypervisor memory regions. The lack of proper isolation enforcement represents a fundamental breakdown in privilege separation mechanisms essential for secure virtualization deployments on ARM hardware.
To mitigate this vulnerability, developers must modify the fix_host_ownership function to explicitly include the per-CPU hyp stack ranges within its traversal logic. This involves extending the walker mechanism used for linear-map regions to also iterate over the private VA range allocated for each CPU's hypervisor stack guard pages and associated memory structures. By ensuring that these critical kernel data segments are subjected to the same ownership verification and adjustment processes as other host-managed memory, the system guarantees correct stage-2 mapping attributes. Administrators should apply available kernel patches or updates provided by their distribution vendors that incorporate this fix. Additionally, rigorous testing of KVM initialization sequences on ARM64 systems is recommended to verify that hyp stack isolation remains intact after applying security updates, ensuring no residual misconfigurations persist in production environments relying on nested virtualization features.