CVE-2024-50022 is a vulnerability identified in the Linux kernel's device-dax subsystem, specifically in the dax_set_mapping() function. The issue arises from improper alignment of the page offset (pgoff) using ALIGN() instead of ALIGN_DOWN(). This misalignment causes the vmf->address to be aligned incorrectly to the next alignment boundary rather than the correct lower boundary. The consequence is that during memory failure handling, particularly in the page_mapped_in_vma() function after a page fault handled by dev_dax_huge_fault, the system may reference an incorrect memory address. This subtle bug manifests primarily under error injection scenarios targeting device-dax regions that are not aligned to the expected device-dax alignment (e.g., 2MB for huge pages). When such unaligned accesses occur, the kernel's memory failure recovery mechanism repeatedly triggers Machine Check Exceptions (MCEs) at the wrong address, causing endless MCE loops and potentially leading to system panic. The vulnerability is difficult to reproduce in typical production environments because device-dax regions are usually pinned and aligned correctly. However, in custom or error-injection testing environments using self-developed dax devices with 2MB aligned mappings, the issue was observed as continuous memory failure logs and uncorrected hardware memory errors. The root cause is the incorrect alignment logic in dax_set_mapping(), which fails to properly identify the task accessing the faulty memory address, preventing the kernel from killing the offending task and recovering gracefully. This vulnerability affects Linux kernel versions identified by the commit hash b9b5777f09be84d0de472ded2253d2f5101427f2 and potentially others with similar device-dax implementations. No known exploits are reported in the wild, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a risk primarily to systems utilizing device-dax for direct access to persistent memory or similar hardware, especially in environments where custom device-dax configurations or error injection testing is performed. The impact includes potential system instability or kernel panics due to endless MCE loops triggered by unaligned memory accesses. This can lead to denial of service conditions affecting critical infrastructure, cloud providers, and data centers relying on Linux servers with device-dax enabled. Confidentiality and integrity impacts are minimal since the vulnerability does not directly allow arbitrary code execution or data leakage. However, availability is significantly impacted due to potential system crashes. Organizations running high-availability services or real-time systems on Linux with device-dax support may experience service disruptions. The subtlety of the bug and its dependence on specific alignment conditions mean that many standard Linux deployments may not be affected, but specialized environments using huge pages and device-dax mappings are at risk. Given the complexity of reproducing the issue, detection and diagnosis require advanced tracing tools like bpftrace, which may limit rapid identification in operational environments.

To mitigate this vulnerability, European organizations should: 1) Apply the latest Linux kernel patches that correct the alignment logic in dax_set_mapping() as soon as they become available from trusted sources or Linux distributions. 2) Audit and verify device-dax configurations to ensure that all device-dax regions are properly pinned and aligned to their expected boundaries (e.g., 2MB for huge pages), avoiding unpinned or unaligned mappings that trigger the bug. 3) Implement enhanced monitoring for MCE logs and memory failure messages to detect symptoms of this issue early, using kernel tracing tools such as bpftrace to correlate page faults and MCE addresses. 4) For environments performing error injection or custom device-dax development, conduct thorough testing with the patched kernel to validate stability and correct memory failure handling. 5) Consider isolating or limiting the use of device-dax features in critical production systems until patches are applied and configurations verified. 6) Engage with Linux vendor support channels for guidance on backported fixes and best practices for device-dax usage. These steps go beyond generic advice by focusing on alignment verification, proactive monitoring, and controlled deployment of device-dax features.