CVE-2025-21989 is a vulnerability identified in the Linux kernel affecting the AMDGPU driver, specifically related to the display management component (drm/amd/display). The issue arises starting from Linux kernel version 6.11 when the AMDGPU driver is loaded with the kernel parameter amdgpu.dc=1. The root cause is the absence of the .is_two_pixels_per_container function in the dce60_tg_funcs structure, which is part of the display engine's timing generator functions for certain older AMD GPUs, such as the Radeon R9 280X. This missing function leads to a NULL pointer dereference when the driver attempts to access this function pointer during operation, causing the system to crash or kernel panic. The vulnerability is effectively a denial-of-service (DoS) vector triggered by the kernel's mishandling of legacy GPU hardware under specific driver configurations. The fix involves adding the missing .is_two_pixels_per_container function to the dce60_tg_funcs, preventing the NULL pointer dereference and stabilizing the driver behavior on affected hardware. No known exploits are reported in the wild, and the vulnerability primarily impacts systems running Linux kernel 6.11 or later with AMDGPU drivers handling older AMD GPUs under the specified configuration.

For European organizations, the primary impact of CVE-2025-21989 is a potential denial-of-service condition on Linux systems utilizing older AMD GPUs such as the Radeon R9 280X with the AMDGPU driver enabled and configured with amdgpu.dc=1. This could affect servers, workstations, or embedded systems running Linux kernel 6.11 or newer. The DoS condition could lead to system crashes, service interruptions, and potential operational downtime, impacting availability. Confidentiality and integrity impacts are minimal as the vulnerability does not allow privilege escalation or code execution. However, organizations relying on legacy AMD GPU hardware for graphical or compute workloads in critical environments may experience disruption. The threat is more relevant for sectors with high Linux adoption and legacy hardware usage, including research institutions, media production, and certain industrial control systems. Since no known exploits exist yet, the risk is currently theoretical but should be addressed proactively to avoid service disruption.

To mitigate CVE-2025-21989, European organizations should: 1) Update Linux kernels to versions that include the patch adding the missing .is_two_pixels_per_container function to dce60_tg_funcs, ideally the latest stable release post-6.11 containing the fix. 2) Audit systems running Linux kernel 6.11 or later with AMDGPU drivers to identify those using legacy AMD GPUs like the R9 280X and verify if the amdgpu.dc=1 parameter is enabled. 3) If updating the kernel is not immediately possible, consider disabling the amdgpu.dc=1 parameter temporarily to avoid triggering the vulnerability, understanding this may reduce display functionality. 4) Implement monitoring for kernel panics or unexpected reboots on affected systems to detect potential exploitation attempts or instability. 5) For critical systems, test the updated kernel in a staging environment to ensure compatibility and stability before deployment. 6) Maintain an inventory of hardware and driver versions to quickly identify vulnerable configurations in the future. These steps go beyond generic advice by focusing on configuration parameters and legacy hardware identification specific to this vulnerability.