CVE-2024-26976 - Resolving Linux Kernel Vulnerability in KVM

In the Linux kernel, a specific vulnerability has been resolved, addressing an issue within the Kernel-based Virtual Machine (KVM) system. This blog post will discuss the details of the vulnerability, CVE-2024-26976, and provide relevant resources for further information.

The vulnerability is found within the KVM subsystem, specifically relating to how the kernel manages the flushing of a vCPU's async page fault (PF) workqueue when the vCPU is being destroyed. By not properly handling this case, KVM might cause a deadlock situation, leading to a potential crash or hang of the host system. The issue is resolved by always flushing the per-vCPU async PF workqueue when a vCPU clears its completion queue, such as when a virtual machine (VM) and all of its virtual CPUs (vCPUs) are being destroyed.

Exploit details can be found in a series of warnings and traces, such as the following

WARNING: CPU: 8 PID: 251 at virt/kvm/kvm_main.c:1435 kvm_put_kvm+x2d/x320 [kvm]
Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel kvm irqbypass
CPU: 8 PID: 251 Comm: kworker/8:1 Tainted: G        W          6.6.-rc1-e7af8d17224a-x86/gmem-vm #119
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS .. 02/06/2015
...

Applying a patch to allow for the correct flushing of workqueues will mitigate this vulnerability, guaranteeing that the KVM _module_ cannot be unloaded until its workqueue callback completes, thus preventing deadlock situations. Additionally, the patch adds a helper to handle "wakeup all" work items correctly, avoiding issues with flushing bogus workqueue entries.

The full details of this vulnerability, and the patch applied to fix it, can be found in the commit message for the applied patch. In this case, see the commit message at: https://lkml.org/lkml/2021/11/20/26

For those using the Linux kernel, it is recommended to update to the latest version or apply the relevant patches to avoid this vulnerability. Further details on kernel vulnerabilities and their CVEs can be found at the following resources:

- Linux Kernel Mailing List: https://lkml.org/
- National Vulnerability Database: https://nvd.nist.gov/

Stay informed on the latest kernel vulnerabilities and updates to ensure that your systems remain secure. In this case, resolving the vulnerability in CVE-2024-26976 will provide improved stability and security for systems using the KVM subsystem within the Linux kernel.

Timeline

Published on: 05/01/2024 06:15:14 UTC
Last modified on: 07/03/2024 01:50:10 UTC