CVE-2024-56559 is a vulnerability identified in the Linux kernel related to the handling of Translation Lookaside Buffer (TLB) flush operations within the Kernel Address Sanitizer (KASAN) shadow virtual address space. Specifically, the issue arises in the memory management subsystem, particularly in the vmalloc area where multiple TLB flush operations are performed inefficiently. When compiling the Linux kernel source code with KASAN enabled on a high-core-count system (e.g., a 256-core machine), a soft lockup occurs due to excessive time spent flushing the TLB repeatedly for each vmalloc area. The root cause is that the kernel code does not combine these flush operations into a single, more efficient operation, leading to a large number of flush_tlb_kernel_range() calls—over 2800 in the observed case—each taking approximately 7.5 milliseconds. This results in a cumulative delay exceeding 20 seconds, triggering the kernel watchdog's soft lockup detection and causing the CPU to appear stuck. The lockup manifests in the kworker kernel thread responsible for draining vmalloc areas, and the kernel stack trace shows the problem is centered around the smp_call_function_many_cond() and related TLB flush functions. The vulnerability is primarily a performance and stability issue rather than a direct security exploit, as it causes a denial of service (DoS) condition by locking up CPUs during kernel compilation or heavy vmalloc usage under KASAN. The issue can be worked around temporarily by extending the soft lockup timeout, but the proper fix involves combining all TLB flush operations into a single operation to reduce overhead. No known exploits are reported in the wild, and the vulnerability affects Linux kernel versions around 6.10.0-rc5 and potentially others using similar vmalloc and KASAN implementations.

For European organizations, the primary impact of CVE-2024-56559 is a potential denial of service condition on Linux systems running KASAN-enabled kernels, especially on high-core-count servers or build systems used for kernel development or testing. Organizations relying on Linux for critical infrastructure, cloud services, or development environments may experience system instability, prolonged CPU lockups, or build failures. This can disrupt continuous integration pipelines, delay software releases, and degrade service availability. While the vulnerability does not directly lead to privilege escalation or data breaches, the induced DoS can impact operational continuity and increase maintenance overhead. Enterprises using Linux in high-performance computing, telecommunications, or research sectors—where large multi-core systems are common—are particularly at risk. Additionally, the issue may affect kernel developers and vendors who compile kernels on large-scale machines, potentially delaying security patch rollouts and updates. Since KASAN is typically enabled in debug or development builds, production systems may be less affected unless they use KASAN for runtime memory error detection. However, any Linux system with similar vmalloc and TLB flush handling could be vulnerable to performance degradation or lockups under specific workloads.

1. Apply the official Linux kernel patch that consolidates TLB flush operations into a single operation during KASAN vmalloc area purging to eliminate the excessive flush overhead. Monitor Linux kernel mailing lists and vendor advisories for the patch release and integrate it promptly. 2. Avoid running KASAN-enabled kernels on production or large multi-core build systems unless necessary, as KASAN increases overhead and may trigger this issue. Use KASAN primarily in controlled development environments. 3. Temporarily increase the kernel watchdog soft lockup timeout to prevent premature CPU lockup detection during heavy vmalloc operations by echoing a higher value to /proc/sys/kernel/watchdog_thresh. 4. Optimize build and testing workflows to reduce parallelism or vmalloc usage on very high-core-count machines until the patch is applied. 5. Monitor system logs for soft lockup warnings related to kworker threads and TLB flush operations to detect potential occurrences early. 6. For organizations using custom or embedded Linux kernels, review vmalloc and KASAN-related code paths for similar inefficiencies and backport fixes as needed. 7. Engage with Linux distribution maintainers to ensure patched kernel versions are included in upcoming stable releases and security updates.