CVE-2021-46920 is a medium-severity vulnerability in the Linux kernel's dmaengine idxd driver component. The issue arises from improper handling of status bits during register writeback operations. Specifically, the current code indiscriminately overwrites the SWERR (software error) and OVERFLOW bits when writing back to a register. This clobbers the OVERFLOW bit that may have been set after the register was read, causing loss of critical error state information. The vulnerability is rooted in the driver blindly writing over these bits instead of preserving the actual bits read from the hardware. This flaw can lead to incorrect error reporting and potentially cause the driver to mismanage hardware error conditions. The idxd driver is responsible for managing Intel Data Streaming Accelerator (DSA) devices, which handle data movement and transformation tasks offloaded from the CPU. The vulnerability does not allow remote exploitation as it requires local access with low privileges (PR:L) and no user interaction (UI:N). The impact is primarily on integrity (I:H) because error states may be mishandled, potentially leading to corrupted data or improper hardware behavior. Availability and confidentiality are not affected. The CVSS 3.1 score is 5.5 (medium severity), reflecting the limited attack vector (local access required) but significant integrity impact. No known exploits are reported in the wild. The fix involves modifying the driver code to write back only the bits actually read, preserving the OVERFLOW bit and preventing clobbering. This vulnerability affects Linux kernel versions containing the vulnerable idxd driver code, identified by the given commit hashes. Since the idxd driver is specific to Intel DSA hardware, only systems using these accelerators are impacted.

For European organizations, the impact depends on the deployment of Linux systems utilizing Intel DSA hardware with the vulnerable idxd driver. Such systems are typically found in data centers, cloud infrastructure, and high-performance computing environments that leverage hardware acceleration for data processing tasks. The vulnerability could lead to silent data integrity issues or hardware mismanagement, potentially causing data corruption or degraded performance in critical workloads. While not directly exploitable remotely, an attacker or malicious insider with local access could exploit this flaw to disrupt data processing integrity. This risk is particularly relevant for sectors relying on Linux-based infrastructure for sensitive data processing, such as finance, telecommunications, research institutions, and government agencies. The lack of impact on confidentiality and availability reduces the risk of data breaches or denial-of-service, but integrity compromise in data handling can have serious downstream effects on decision-making, compliance, and operational reliability.

European organizations should prioritize updating their Linux kernel to versions that include the patch fixing CVE-2021-46920. Specifically, they should track kernel releases from their Linux distribution vendors or directly apply patches to the idxd driver code to ensure proper handling of SWERR and OVERFLOW bits. Since the vulnerability requires local access, organizations should also enforce strict access controls and monitoring on systems with Intel DSA hardware to prevent unauthorized local usage. Implementing kernel integrity monitoring and auditing can help detect anomalous driver behavior. For environments using containerization or virtualization, ensure that host kernels are patched, as guest OS kernels may not expose this vulnerability directly. Additionally, organizations should review their hardware inventory to identify systems with Intel DSA accelerators and assess the risk exposure. Where possible, disable or restrict use of the idxd driver if the hardware is not in active use. Finally, maintain up-to-date incident response plans to address potential integrity issues arising from this vulnerability.