Bug 2562778 (CVE-2026-99168)

Summary:	CVE-2026-99168 kernel: mshv_vtl: Check per-CPU register page before mmap
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 Linux kernel's Microsoft Hyper-V Virtual Trust Level (mshv_vtl) driver. When setting up per-processor register pages, an allocation failure on one CPU leaves its page pointer uninitialized while a global flag is set by another CPU. A local user can exploit this issue by accessing the unallocated register memory mapping, causing the kernel to dereference a null pointer. The primary impact of this vulnerability is a system crash, resulting in a Denial of Service (DoS).	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 2026-10-28 11:07:14 UTC

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

mshv_vtl: Check per-CPU register page before mmap

Register-page setup is optional for each CPU. If allocation or
registration fails, mshv_vtl_configure_reg_page() warns and leaves that
CPU's reg_page NULL, but initial context setup continues successfully.
Meanwhile, successful setup on another CPU sets the global
mshv_has_reg_page flag.

mshv_vtl_fault() checks this global flag before selecting the requested
CPU's register page. With mixed setup results across online CPUs, the
check passes even for a CPU with no register page, reaching
get_page(NULL) when userspace faults in that mapping.

Check the selected per-CPU register page before taking its reference and
return VM_FAULT_SIGBUS if it is absent.

Comment 1 gkamathe 2026-10-28 21:08:48 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-99168.mbox