Bug 2464387 (CVE-2026-31735)

Summary:	CVE-2026-31735 kernel: iommupt: Fix short gather if the unmap goes into a large mapping
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
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's Input/Output Memory Management Unit (IOMMU) page table handling. When an unmap operation partially overlaps with a large memory mapping, the system's invalidation process may not correctly flush the entire unmapped range. This could result in a 'short invalidation,' where some memory remains improperly invalidated. While this issue could potentially lead to data integrity problems or information disclosure, it is currently considered unlikely to be a triggerable bug.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
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Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-05-01 15:03:53 UTC

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

iommupt: Fix short gather if the unmap goes into a large mapping

unmap has the odd behavior that it can unmap more than requested if the
ending point lands within the middle of a large or contiguous IOPTE.

In this case the gather should flush everything unmapped which can be
larger than what was requested to be unmapped. The gather was only
flushing the range requested to be unmapped, not extending to the extra
range, resulting in a short invalidation if the caller hits this special
condition.

This was found by the new invalidation/gather test I am adding in
preparation for ARMv8. Claude deduced the root cause.

As far as I remember nothing relies on unmapping a large entry, so this is
likely not a triggerable bug.

Comment 1 Keith Grant 2026-05-01 21:24:38 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050138-CVE-2026-31735-436c@gregkh/T