Bug 2507128 (CVE-2026-64284)

Summary: CVE-2026-64284 kernel: KVM: x86: Ensure vendor's exit handler runs before fastpath userspace exits
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's Kernel-based Virtual Machine (KVM) for x86 systems. This vulnerability occurs when KVM handles fastpath exits, where it may fail to execute vendor-specific cleanup operations before returning control to the virtual machine's userspace. Consequently, memory written by the virtual machine might not be correctly flagged as dirty, leading to the consumption of outdated data. A local attacker with access to a virtual machine could potentially exploit this to cause data integrity issues within the virtualized environment.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-07-25 10:06:30 UTC 
In the Linux kernel, the following vulnerability has been resolved:

KVM: x86: Ensure vendor's exit handler runs before fastpath userspace exits

Move the handling of fastpath userspace exits into vendor code to ensure
KVM runs vendor specific operations that need to run before userspace gains
control of the vCPU.  E.g. for VMX (and soon to be for SVM as well), KVM
needs to flush the PML buffer prior to exiting to userspace, otherwise any
memory written by the final KVM_RUN might never be flagged as dirty.

Note, waiting to snapshot CR0 and CR3 until svm_handle_exit() is flawed in
general, as that risks consuming stale state in a fastpath handler.  That
will be addressed in a future change.
Comment 1 TEJ RATHI 2026-07-29 16:23:39 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026072503-CVE-2026-64284-260f@gregkh/T