CVE-2026-89909 Overview
CVE-2026-89909 affects the Linux kernel's LoongArch Kernel-based Virtual Machine (KVM) subsystem. The flaw involves a resource leak that occurs when kvm_init() fails during module initialization. The kvm_loongarch_init() function calls kvm_loongarch_env_init() to allocate per-CPU kvm_context (vmcs) and kvm_loongarch_ops, and to register performance callbacks. When kvm_init() subsequently fails, the function returns the error directly without invoking kvm_loongarch_env_exit(). Because module_init() does not execute the module_exit() path on failure, the allocated resources are never released.
Critical Impact
Failed KVM module initialization on LoongArch systems leaks per-CPU memory allocations and leaves stale perf callbacks registered, degrading kernel resource integrity.
Affected Products
- Linux kernel (LoongArch architecture, KVM subsystem)
- Stable kernel branches referenced by upstream commits 3bf6f5e2, 6b78786e, 6bbbd7b7, and f7a1064c
- Distributions shipping LoongArch KVM support prior to the fix
Discovery Timeline
- 2026-09-16 - CVE-2026-89909 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-89909
Vulnerability Analysis
The defect resides in the LoongArch KVM initialization path. kvm_loongarch_init() performs two sequential setup steps. First, it calls kvm_loongarch_env_init(), which allocates per-CPU kvm_context structures used as the virtual machine control state (vmcs), allocates kvm_loongarch_ops, and registers perf callbacks. Second, it calls the generic kvm_init() to complete KVM registration.
If kvm_init() returns an error, kvm_loongarch_init() propagates that error directly to the caller. The Linux module framework treats a non-zero return from a module_init() function as a load failure and does not invoke the corresponding module_exit() routine. As a result, kvm_loongarch_env_exit() never runs, and the resources allocated in the first step remain allocated.
Root Cause
The root cause is a missing teardown-on-failure step in kvm_loongarch_init(). The function does not follow the pattern used by riscv_kvm_init(), which explicitly calls its environment-exit helper when the generic kvm_init() fails. The absence of this cleanup produces a memory leak of per-CPU state and leaves registered perf callbacks pointing at code that is about to be unloaded, classifying the issue as a Memory Leak [CWE-401] with related unclean-shutdown behavior.
Attack Vector
Exploitation requires triggering kvm_init() failure during LoongArch KVM module load. This is not a network-reachable condition. It is exercised by kernel developers, automated test harnesses, or systems where KVM initialization fails due to hardware, configuration, or resource pressure. Repeated module load attempts amplify the leak. The vulnerability does not, on its own, provide code execution or privilege escalation.
The upstream fix adds a call to kvm_loongarch_env_exit() on the kvm_init() failure path, mirroring the RISC-V implementation. See the fix commits in the kernel git tree for the exact code change.
Detection Methods for CVE-2026-89909
Indicators of Compromise
- Increasing kernel memory consumption on LoongArch hosts after failed kvm module load attempts.
- Presence of orphaned perf callbacks referencing LoongArch KVM symbols after the module fails to load.
- Kernel log entries showing kvm_init() failure without subsequent teardown messages from kvm_loongarch_env_exit().
Detection Strategies
- Audit LoongArch kernel builds against the fix commits 3bf6f5e2, 6b78786e, 6bbbd7b7, and f7a1064c to confirm the teardown path is present.
- Use kernel memory leak detectors such as kmemleak during module load and unload cycles on LoongArch test systems.
- Instrument CI pipelines to force kvm_init() failure and verify that per-CPU KVM structures are freed.
Monitoring Recommendations
- Track kernel Slab and per-CPU allocator counters on LoongArch virtualization hosts, especially after modprobe kvm failures.
- Alert on repeated module load failures for the LoongArch KVM module in dmesg and journal logs.
- Correlate KVM module lifecycle events with host memory pressure metrics to identify slow leaks.
How to Mitigate CVE-2026-89909
Immediate Actions Required
- Apply the stable kernel updates that include the upstream fix commits referenced by this CVE.
- Avoid repeated modprobe kvm retries on LoongArch hosts running unpatched kernels, since each failed attempt compounds the leak.
- Restrict module load privileges to trusted administrators to prevent unnecessary initialization cycles.
Patch Information
The fix adds a call to kvm_loongarch_env_exit() when kvm_init() fails, matching the teardown-on-failure pattern used by riscv_kvm_init(). Merged fixes are available in the following commits: Kernel Git Commit 3bf6f5e, Kernel Git Commit 6b78786e, Kernel Git Commit 6bbbd7b7, and Kernel Git Commit f7a1064c. Rebuild and reboot LoongArch hosts after applying the update.
Workarounds
- Disable automatic loading of the LoongArch KVM module on hosts that do not require virtualization until the patched kernel is deployed.
- Reboot LoongArch systems that have accumulated leaked resources from prior failed KVM initialization attempts to reclaim kernel memory.
- Pin LoongArch virtualization workloads to hosts running kernels that already include the referenced fix commits.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
