CVE-2023-52761 is a vulnerability in the Linux kernel specifically affecting the RISC-V architecture's kernel stack overflow detection mechanism when CONFIG_VMAP_STACK is enabled. The vulnerability arises from a race condition between multiple CPUs (harts) that overflow their kernel stacks simultaneously. The original implementation introduced a 'shadow_stack' to temporarily handle overflow, but this shadow stack was not per-CPU, leading to potential corruption when two CPUs concurrently overflowed their kernel stacks. This could cause one or both CPUs to corrupt each other's state, resulting in kernel instability or crashes. The patch removes the shared shadow_stack and instead switches directly to a per-CPU overflow stack, ensuring thread safety and preventing cross-CPU state corruption. The fix involves defining an assembly macro to obtain per-CPU symbols and modifying the kernel entry assembly code to use this macro to select the correct per-CPU overflow stack. The vulnerability was demonstrated by a kernel crash triggered via the debug interface, showing a kernel panic due to stack overflow. This issue is specific to the RISC-V port of the Linux kernel and affects kernel versions around 6.1.0-rc2. No known exploits are reported in the wild yet, and no CVSS score has been assigned. The vulnerability impacts kernel stability and could lead to denial of service via kernel panic or system crash if exploited, especially in multi-core RISC-V systems running Linux with VMAP_STACK enabled.

For European organizations, the impact of CVE-2023-52761 primarily concerns systems running Linux on RISC-V architecture with VMAP_STACK enabled. While RISC-V adoption in Europe is currently limited compared to x86 and ARM, it is growing in embedded systems, IoT devices, and specialized computing environments. Organizations using RISC-V Linux kernels in critical infrastructure, industrial control systems, or research environments could face system instability or denial of service due to kernel panics caused by this vulnerability. This could disrupt operations, cause data loss, or require costly system reboots and troubleshooting. Since the vulnerability involves kernel stack overflow handling, it could also complicate debugging and recovery processes. Although no direct remote exploitation or privilege escalation is indicated, the denial of service impact on multi-core RISC-V Linux systems could affect availability of services, particularly in environments relying on RISC-V for edge computing or embedded applications. European organizations developing or deploying RISC-V Linux systems should prioritize patching to maintain system reliability and avoid operational disruptions.

1. Apply the official Linux kernel patch that replaces the shared shadow_stack with a per-CPU overflow stack as soon as it becomes available in your kernel distribution or upstream kernel source. 2. For organizations compiling their own kernels, ensure CONFIG_VMAP_STACK is enabled only if the patched kernel version is used. 3. Conduct thorough testing of multi-core RISC-V Linux systems under high stack usage scenarios to detect potential stack overflow issues. 4. Monitor kernel debug interfaces and logs for signs of stack overflow or kernel panics related to this vulnerability. 5. Limit access to kernel debug interfaces (e.g., /sys/kernel/debug) to trusted administrators to prevent accidental or malicious triggering of stack exhaustion. 6. For embedded or IoT devices using RISC-V Linux, coordinate with hardware and software vendors to ensure timely firmware and kernel updates. 7. Implement robust system monitoring and automated recovery mechanisms to minimize downtime in case of kernel panics. 8. Consider disabling VMAP_STACK if not strictly required and if doing so does not compromise other security or stability features, as a temporary workaround until patched kernels are deployed.