CVE-2024-42293 is a vulnerability identified in the Linux kernel specifically affecting the arm64 architecture when using 16K pages combined with 4-level page tables where the fourth level is folded at runtime due to the absence of LPA2 (Large Physical Address Extension 2). The issue arises in the fast Get User Pages (GUP) code path, which is responsible for quickly walking page tables to pin user-space pages in memory. The vulnerability is caused by the generic implementation of the function p4d_offset_lockless(), which returns a pointer to a 'p4d_t' structure allocated on the stack within the caller function gup_fast_pgd_range(). Normally, this is safe; however, when the fourth page-table level is folded at runtime, the subsequent call to pud_offset_lockless() calculates the address of the PUD (Page Upper Directory) by offsetting from the stack-allocated p4d_t pointer. This results in a stray read from the stack memory, which can cause the page-table walker to behave unpredictably, potentially leading to random kernel oops (crashes) or memory corruption. The fix implemented involves redefining p4d_offset_lockless() for configurations where CONFIG_PGTABLE_LEVELS is less than or equal to 4, ensuring it returns a pointer to the actual page-table structure instead of a local stack variable. This correction prevents the invalid memory access and stabilizes the page-table walking process. No known exploits are reported in the wild at this time, and the vulnerability is primarily a stability and memory safety issue within the kernel's memory management subsystem on affected arm64 systems.

For European organizations, the impact of CVE-2024-42293 depends largely on their use of arm64-based Linux systems, particularly those configured with 16K pages and 4-level page tables with folding enabled. This vulnerability can cause random kernel crashes (oops) and potential memory corruption, which may lead to denial of service (DoS) conditions on critical servers or embedded devices running vulnerable kernels. Such instability can disrupt business operations, especially in environments relying on arm64 servers for cloud infrastructure, edge computing, or IoT deployments. While there is no direct evidence of privilege escalation or arbitrary code execution, the kernel crashes could be exploited by attackers to cause service interruptions or to aid in further attacks by destabilizing systems. European organizations in sectors such as telecommunications, manufacturing, and cloud services that deploy arm64 Linux servers or appliances may face increased operational risk until patched. Additionally, the lack of a CVSS score and no known exploits suggest the threat is currently moderate but should be addressed proactively to maintain system reliability and security.

To mitigate CVE-2024-42293, European organizations should: 1) Identify all Linux systems running on arm64 architecture with 16K page size and 4-level page tables with folding enabled. This may require auditing kernel configurations and hardware specifications. 2) Apply the official Linux kernel patches that redefine p4d_offset_lockless() as per the fix described, ensuring the kernel version includes the correction for this vulnerability. 3) For systems where immediate patching is not feasible, consider disabling the use of 16K pages or adjusting page-table levels if possible, to avoid triggering the vulnerable code path. 4) Monitor kernel logs for random oops or memory corruption symptoms that could indicate exploitation or triggering of this issue. 5) Engage with Linux distribution vendors to obtain timely updates and backported patches for enterprise kernels. 6) Incorporate this vulnerability into vulnerability management and incident response plans to ensure rapid detection and remediation. 7) For embedded or specialized devices using arm64 Linux kernels, coordinate with device manufacturers to obtain firmware or kernel updates addressing this issue.