CVE-2021-46918: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-46918 affects the Linux kernel's DMA engine, specifically the IDXD (Intel Data Streaming Accelerator) driver. The vulnerability was discovered in versions from 5.11.0 up to (excluding) 5.11.16. The issue involves improper handling of MSIX permission entries during device shutdown, where the code left MSIX enabled and PASID entries still programmed at device shutdown (NVD).

The vulnerability stems from a missing cleanup operation in the IDXD driver where MSIX permission entries were not properly cleared during device shutdown. While the driver correctly set up MSIX permissions during device initialization, it failed to clear these permissions during shutdown. The issue has a CVSS v3.1 base score of 5.5 MEDIUM with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD, Red Hat).

The vulnerability primarily affects system availability. When exploited, it could potentially lead to system instability or denial of service conditions due to improperly cleared MSIX permission entries during device shutdown (Red Hat).

The issue has been fixed by adding proper cleanup of MSIX permission entries during device shutdown. The fix involves implementing two new functions: idxd_msix_perm_setup() and idxd_msix_perm_clear() to properly handle MSIX permissions. The patch ensures that MSIX permission entries are cleared during device shutdown, mirroring the setup process during initialization (Kernel Patch).