CVE-2024-45818: Deadlock in x86 HVM standard VGA handling
First published: Tue Nov 12 2024(Updated: )
The hypervisor contains code to accelerate VGA memory accesses for HVM guests, when the (virtual) VGA is in "standard" mode. Locking involved there has an unusual discipline, leaving a lock acquired past the return from the function that acquired it. This behavior results in a problem when emulating an instruction with two memory accesses, both of which touch VGA memory (plus some further constraints which aren't relevant here). When emulating the 2nd access, the lock that is already being held would be attempted to be re-acquired, resulting in a deadlock. This deadlock was already found when the code was first introduced, but was analysed incorrectly and the fix was incomplete. Analysis in light of the new finding cannot find a way to make the existing locking discipline work. In staging, this logic has all been removed because it was discovered to be accidentally disabled since Xen 4.7. Therefore, we are fixing the locking problem by backporting the removal of most of the feature. Note that even with the feature disabled, the lock would still be acquired for any accesses to the VGA MMIO region.
Credit: security@xen.org
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Xen Hypervisor | >=4.7 |
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Reference Links
Frequently Asked Questions
What is the severity of CVE-2024-45818?
CVE-2024-45818 has a high severity rating due to the potential for exploitation impacting hypervisor stability.
How do I fix CVE-2024-45818?
To resolve CVE-2024-45818, users should upgrade to the latest version of the Xen Hypervisor where this vulnerability has been addressed.
Which versions of Xen Hypervisor are affected by CVE-2024-45818?
CVE-2024-45818 affects Xen Hypervisor versions starting from 4.7.
What are the potential impacts of CVE-2024-45818 on HVM guests?
The potential impacts of CVE-2024-45818 include degraded performance and stability issues for HVM guests due to improper locking behavior.
Is there a workaround for CVE-2024-45818?
Currently, there are no confirmed workarounds for CVE-2024-45818 other than upgrading to a patched version of the Xen Hypervisor.
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