CVE-2021-47414 is a vulnerability identified in the Linux kernel specifically affecting the RISC-V architecture implementation. The issue arises during the kernel's function patching process, particularly when the ftrace subsystem attempts to patch the function riscv_cpuid_to_hartid_mask. The vulnerability manifests as an illegal instruction exception leading to a kernel panic and system crash. The root cause is a failure to properly synchronize the instruction cache (icache) of the current CPU before requesting other CPUs to flush their caches. The patch_text_nosync function modifies instructions and calls flush_icache_range, which cascades to flush_icache_all and eventually to sbi_remote_fence_i and __sbi_rfence_v02. However, the current CPU's icache and data cache are not flushed before invoking riscv_cpuid_to_hartid_mask, causing the CPU to execute stale or invalid instructions. This results in an illegal instruction fault and a kernel panic, effectively halting the system. The fix involves explicitly flushing the current CPU's icache before triggering remote CPU cache flushes, ensuring cache coherency and preventing the illegal instruction execution. This vulnerability is specific to Linux kernel versions containing the affected commit (fab957c11efe2f405e08b9f0d080524bc2631428) and impacts systems running on SiFive HiFive Unmatched and potentially other RISC-V hardware platforms using the affected kernel versions. There are no known exploits in the wild, and no CVSS score has been assigned yet.

For European organizations, the impact of CVE-2021-47414 is primarily on systems running Linux on RISC-V hardware, such as the SiFive HiFive Unmatched platform. While RISC-V adoption in Europe is currently limited compared to x86 and ARM architectures, this vulnerability could affect research institutions, embedded systems developers, and companies experimenting with or deploying RISC-V based solutions. The vulnerability leads to kernel panics and system crashes, causing denial of service (DoS) conditions. In critical infrastructure or industrial control systems using RISC-V Linux kernels, this could disrupt operations and lead to downtime. Additionally, the inability to patch kernel functions safely could hinder debugging and kernel tracing activities, impacting system stability and maintenance. Although no direct exploitation for privilege escalation or data compromise is indicated, the denial of service impact on availability can be significant in production environments. Organizations relying on RISC-V Linux systems must be aware of this flaw to avoid unexpected system failures.

To mitigate CVE-2021-47414, European organizations should: 1) Update the Linux kernel to a version that includes the fix for this vulnerability, ensuring the patch that flushes the current CPU's icache before remote CPU cache flushes is applied. 2) For systems where immediate kernel updates are not feasible, avoid enabling or using ftrace or other kernel tracing features that trigger function patching on affected RISC-V platforms. 3) Conduct thorough testing of kernel updates in controlled environments to verify stability and absence of illegal instruction faults. 4) Monitor kernel logs for signs of illegal instruction exceptions or kernel panics related to riscv_cpuid_to_hartid_mask or ftrace activities. 5) Engage with hardware vendors and Linux distribution maintainers to obtain timely patches and guidance specific to RISC-V hardware. 6) For embedded or industrial deployments, implement redundancy and failover mechanisms to minimize downtime caused by potential kernel panics. 7) Maintain an inventory of RISC-V Linux systems to prioritize patching and risk assessment.