Linux Kernel Vulnerability Affecting KVM Functionality

CVE-2026-89775

What is CVE-2026-89775?

CVE-2026-89775 is a vulnerability identified in the Linux kernel, specifically affecting the Kernel-based Virtual Machine (KVM) functionality for the arm64 architecture. This vulnerability arises during the evaluation of Translation Lookaside Buffer (TLB) size during address space management operations. The issue is rooted in how the kernel handles negative values related to S1 walk levels when computing the results of TLB invalidation processes.

The mismanagement of these negative levels can lead to an improper evaluation, where functions such as pgshift_level_to_ttl() do not correctly interpret negative inputs, leading to a TLB invalidation size of 0. This flawed interpretation can have serious implications, particularly with respect to memory management and virtual machine operations. If exploited, it could enable unauthorized or unintended access to the resources managed by the kernel, potentially affecting the stability and security of systems utilizing KVM for virtualization.

Potential impact of CVE-2026-89775

1. Resource Mismanagement: The vulnerability can lead to incorrect memory mapping evaluations, resulting in possible resource allocations that do not reflect the actual requirements of the virtual machines. Such discrepancies could lead to performance issues or instability in systems operating under heavy loads.

2. Unauthorized Information Access: Given that TLB mappings play a crucial role in memory protection and process isolation, a failure in their handling may expose sensitive information across different virtual machines or processes within the same environment, increasing the risk of data breaches.

3. Operational Disruptions: The improper handling of TLB invalidations could potentially lead to system crashes or VM failures, disrupting services that rely on KVM for virtualization. This can have cascading effects on operational processes, particularly in critical infrastructure environments.

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CVE-2026-89775

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