CVE-2026-98653: KVM: s390: Fix _gaccess_shadow_fault()

CVE-2026-98653: KVM: s390: Fix _gaccess_shadow_fault()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

KVM: s390: Fix _gaccess_shadow_fault()

In some circumstances, it is possible that the page of nested guest
memory that is being shadowed is not present at all in the parent guest
gmap. dat_entry_walk() will not find any leaf entry and return with
-ENOENT, which will erroneously be propagated all the way to userspace.

Fix by manually calling gmap_link() on the memory of the nested guest
that is being shadowed if the mapping was not already present.

The Linux kernel CVE team has assigned CVE-2026-98653 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 7.0 with commit e38c884df92119d96f652d51f82661dd2fc0b885 and fixed in 7.2.9 with commit 94c43c7df46433ed4d1e18f13770b019ba977bd8
	Issue introduced in 7.0 with commit e38c884df92119d96f652d51f82661dd2fc0b885 and fixed in 7.3-rc5 with commit faff4c8ff3dbec6d71b89dd281a0d17c4478fa44

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-98653
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/s390/kvm/s390/gaccess.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/94c43c7df46433ed4d1e18f13770b019ba977bd8
	https://git.kernel.org/stable/c/faff4c8ff3dbec6d71b89dd281a0d17c4478fa44