CVE-2024-26620: 
Linux Kernel vulnerability analysis and mitigation

CVE-2024-26620 is a vulnerability in the Linux kernel's s390/vfio-ap subsystem, discovered in early 2024. The issue affects the vfio_ap_mdev_filter_matrix function, which is responsible for updating guest AP configurations when new adapters or domains are assigned to the mdev. The vulnerability impacts Linux kernel versions from 6.0 up to (excluding) 6.1.76, versions from 6.2 up to (excluding) 6.6.15, and versions from 6.7 up to (excluding) 6.7.3 (NVD).

The vulnerability occurs in the vfio_ap_mdev_filter_matrix function's inspection process. When an adapter or domain is assigned, the function only inspects APQNs associated with the APID of the new adapter or APQI of the new domain. This limited inspection can result in AP queues being passed through to a guest even when they are not bound to the vfio_ap device driver, violating the Linux device model requirement that guests should only access devices bound to the driver facilitating their pass-through (Kernel Patch). The vulnerability has been assigned a CVSS v3.1 Base Score of 7.5 HIGH with vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (NVD).

The vulnerability allows AP queues to be passed through to a guest that are not properly bound to the vfio_ap device driver. This can lead to unauthorized access to devices and potential security implications in virtualized environments, particularly affecting systems using the s390 architecture's AP (Adjunct Processor) interface (Kernel Patch).

The vulnerability can be triggered under specific circumstances, such as when unassigning and reassigning domains while certain queue configurations are in place. For example, with a guest's AP configuration including multiple APQNs (e.g., 14.0004, 14.0005, 14.0006, 16.0004, 16.0005, 16.0006), unassigning domain 4, unbinding queue 16.0005, and then reassigning domain 4 can lead to unauthorized queue access (Kernel Patch).

The vulnerability has been fixed by modifying the vfio_ap_mdev_filter_matrix function to inspect every adapter and domain assigned to the mdev when filtering the mdev's matrix, rather than only checking the newly assigned components. This ensures comprehensive validation of all queue assignments (Kernel Patch).