Bug 2482050 (CVE-2026-46071)

Summary:	CVE-2026-46071 kernel: KVM: nSVM: Avoid clearing VMCB_LBR in vmcb12
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	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) subsystem, specifically affecting its nested virtualization (nSVM) capabilities. The issue arises from incorrect handling of Virtual Machine Control Block Last Branch Record (VMCB_LBR) data when copied to vmcb12, an operation that is not architecturally defined. This can lead to unexpected behavior or instability within nested virtualized environments, potentially impacting the reliability of guest virtual machines.	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 2026-05-27 15:08:52 UTC

In the Linux kernel, the following vulnerability has been resolved:

KVM: nSVM: Avoid clearing VMCB_LBR in vmcb12

svm_copy_lbrs() always marks VMCB_LBR dirty in the destination VMCB.
However, nested_svm_vmexit() uses it to copy LBRs to vmcb12, and
clearing clean bits in vmcb12 is not architecturally defined.

Move vmcb_mark_dirty() to callers and drop it for vmcb12.

This also facilitates incoming refactoring that does not pass the entire
VMCB to svm_copy_lbrs().

Comment 1 Keith Grant 2026-05-27 17:50:54 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026052758-CVE-2026-46071-d16a@gregkh/T