A recent vulnerability in the Linux kernel was identified and addressed, specifically in the dmaengine subsystem, which handles direct memory access (DMA) operations. The vulnerability, labeled as CVE-2021-46918, defines an issue related to the improper handling of MSIX permission entries during a device's shutdown process. The potential exploit could lead to unauthorized access to system resources and cause unexpected behaviors.

Vulnerability Details

The dmaengine subsystem in the Linux kernel facilitates DMA operations that allow a device to send data directly to or from system memory. The Intel Data Direct I/O Technology (DDIO) device, also known as the idxd driver, relies on the MSI-X (Message Signal-Based Interrupt Extension) capability to handle DMA-related interrupt events.

The issue with the idxd driver was that the MSIX permission entries were not being properly cleared during the device shutdown process. This left MSIX enabled, and the pasid (Process Address Space ID) entries programmed even after the device had shut down. This oversight could lead to unauthorized access to system memory, leading to potential information leaks or system instability.

Resolution

To resolve this vulnerability, developers added a code snippet to disable and clear MSIX permission entries during the device shutdown process, mirroring the enabling of MSIX entries during the device's startup or probe. The updated code snippet is as follows:

static void idxd_shutdown(struct idxd_device *idxd)
{
    ...
+   idxd_disable_msix(idxd);
    ...
+  idxd_mask_msix_vectors(idxd);
}

This fix ensures that MSIX is disabled and all associated pasid entries are cleaned up upon device shutdown, preventing possible exploits.

The vulnerability was reported and addressed through the following patches

1. dmaengine: idxd: clear MSIX permission entry on shutdown - Patchwork (lkml.org)
2. CVE-2021-46918 - Red Hat Customer Portal

Exploit Details

As of now, there are no known exploits or proof of concept (PoC) implementations identified in the wild. However, system administrators and users are strongly encouraged to apply the latest Linux kernel updates or patches mentioned in the references above to mitigate the potential risk associated with this vulnerability.

Conclusion

The CVE-2021-46918 vulnerability highlights a security risk in the dmaengine subsystem of the Linux kernel due to improper handling of MSIX permission entries during the device shutdown process. The vulnerability has been fixed by including a code snippet to disable and clear the MSIX permission entries upon shutdown, providing a more secure shutdown process. Always keep your system up-to-date to minimize the risk of vulnerabilities and ensure the best possible security measures are in place.

Timeline

Published on: 02/27/2024 07:15:08 UTC
Last modified on: 04/10/2024 14:47:16 UTC