Bug 2535216 (CVE-2026-89921)

Summary:	CVE-2026-89921 kernel: KVM: s390: Zero initialize data structures for inject_pfault_token
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, 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 Kernel-based Virtual Machine (KVM) for the s390 architecture in the Linux kernel. The `__kvm_inject_pfault_token()` function fails to fully zero-initialize certain data structures, specifically `struct kvm_s390_irq`. This oversight allows stale stack values to persist in the `ext_params` and `pad` fields. A local host user could exploit this by using migration input/output controls (ioctls) to access this uninitialized data, leading to information disclosure.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-16 11:35:48 UTC

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

KVM: s390: Zero initialize data structures for inject_pfault_token

__kvm_inject_pfault_token() only sets .type and .u.ext.ext_params2 of
the on-stack struct kvm_s390_irq but the full ext substructure is copied
into the cpu local variable on inject. ext_params and pad contain stale
stack values.

Interrupt delivery only uses ext_params2, so nothing leaks to the guest,
but a host user can use the migration ioctls to get to the data.

Fix by zero-initializing the irq struct.
Do the same for the inti data structure.

Comment 1 Keith Grant 2026-09-16 15:34:32 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89921.mbox