Bug 2422662 (CVE-2025-68179)

Summary:	CVE-2025-68179 kernel: Linux kernel (s390): Denial of service and data corruption due to improper page table updates
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:	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 on the s390 architecture. A local user with low privileges could trigger a vulnerability by enabling ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP. This issue arises because kernel page table entries are modified without properly flushing the Translation Lookaside Buffer (TLB), which can lead to system crashes and potential data corruption. This could result in a denial of service.	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 2025-12-16 14:01:50 UTC

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

s390: Disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP

As reported by Luiz Capitulino enabling HVO on s390 leads to reproducible
crashes. The problem is that kernel page tables are modified without
flushing corresponding TLB entries.

Even if it looks like the empty flush_tlb_all() implementation on s390 is
the problem, it is actually a different problem: on s390 it is not allowed
to replace an active/valid page table entry with another valid page table
entry without the detour over an invalid entry. A direct replacement may
lead to random crashes and/or data corruption.

In order to invalidate an entry special instructions have to be used
(e.g. ipte or idte). Alternatively there are also special instructions
available which allow to replace a valid entry with a different valid
entry (e.g. crdte or cspg).

Given that the HVO code currently does not provide the hooks to allow for
an implementation which is compliant with the s390 architecture
requirements, disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP again, which is
basically a revert of the original patch which enabled it.

Comment 1 Alexander B 2025-12-17 04:59:18 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025121631-CVE-2025-68179-6ce9@gregkh/T