CVE-2024-38667 is a vulnerability identified in the Linux kernel specifically affecting the RISC-V architecture implementation. The issue arises from improper handling of the kernel thread stack for secondary idle threads (secondary boot harts). In the Linux kernel, the top of the kernel thread stack is reserved for the pt_regs structure, which stores processor register states during context switches and interrupts. However, for secondary idle threads, this reservation was not correctly implemented, leading to an overlap between the stack and the pt_regs structure. This overlap can cause corruption of the pt_regs data, including critical fields such as the status register. The vulnerability was discovered during CPU hotplug tests with virtualization (V) enabled, where the smp_callin function stored several registers on the stack, inadvertently corrupting the pt_regs structure. This corruption leads the kernel to attempt saving or restoring a non-existent virtualization context, which could cause kernel instability or crashes. A similar issue had been fixed previously for the primary hart, but the fix was not propagated to secondary harts, leaving this vulnerability unaddressed until now. The vulnerability affects Linux kernel versions identified by the commit hash 2875fe0561569f82d0e63658ccf0d11ce7da8922, indicating a specific code state rather than a broad version range. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet. The vulnerability is technical and low-level, impacting kernel thread stack management on RISC-V platforms, which are increasingly used in specialized and emerging computing environments.

For European organizations, the impact of CVE-2024-38667 depends largely on their use of Linux systems running on RISC-V architecture processors. While RISC-V is gaining traction, it is still less common than x86 or ARM in mainstream enterprise environments. However, sectors investing in RISC-V for research, embedded systems, or specialized computing (such as telecommunications, automotive, or industrial control) could be affected. The vulnerability could lead to kernel crashes or instability, potentially causing denial of service conditions on critical systems. This may disrupt operations, especially in environments requiring high availability or real-time processing. Additionally, corrupted kernel states could complicate debugging and recovery, increasing downtime. Since the vulnerability involves kernel thread stack corruption, it could also affect virtualization environments running on RISC-V, impacting cloud or edge computing services. Although no direct exploitation is known, the risk of future exploitation exists if attackers find ways to trigger the corruption remotely or escalate privileges. European organizations relying on RISC-V Linux systems should consider this vulnerability seriously to maintain system stability and security.

To mitigate CVE-2024-38667, European organizations should: 1) Apply the official Linux kernel patch that addresses the stack reservation issue for secondary idle threads on RISC-V architectures as soon as it is released and tested in their environment. 2) Conduct thorough testing of kernel updates in staging environments, especially for systems utilizing CPU hotplug features and virtualization, to ensure stability and compatibility. 3) Monitor kernel mailing lists and security advisories for updates or additional patches related to this vulnerability. 4) Limit the use of CPU hotplug and virtualization features on RISC-V systems until patches are applied, if feasible, to reduce the attack surface. 5) Implement robust monitoring and alerting for kernel crashes or unusual system behavior that might indicate exploitation attempts or instability caused by this vulnerability. 6) Engage with hardware and software vendors to confirm RISC-V platform support and timely patch deployment. 7) For critical systems, consider fallback or redundancy strategies to maintain availability during patching or in case of instability.