CVE-2026-89912: KVM: arm64: vgic-its: Don't dereference a NULL collection on ITT save

CVE-2026-89912: KVM: arm64: vgic-its: Don't dereference a NULL collection on ITT save

[Greg Kroah-Hartman]

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

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

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

KVM: arm64: vgic-its: Don't dereference a NULL collection on ITT save

MAPC with V=0 drops ite->collection but leaves the ITE on the device's
ITT list, and vgic_its_save_ite() dereferences it unconditionally. A
guest that issues MAPD, MAPTI and then MAPC(V=0) therefore oopses the
host when the VMM issues KVM_DEV_ARM_ITS_SAVE_TABLES to migrate it.
That sequence is UNPREDICTABLE per the architecture, but KVM already
handles the resulting state in the translate, MOVI and DISCARD paths.

Save a zeroed entry, which vgic_its_restore_ite() reads back as
invalid. Skipping the ITE instead would leave the ITT slot holding
whatever is in guest memory, and restore rejects an entry naming a
collection the restored collection table does not have.

The Linux kernel CVE team has assigned CVE-2026-89912 to this issue.


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

	Issue introduced in 4.12 with commit eff484e0298da5a4d18ca82f5454c557fd942af5 and fixed in 6.18.51 with commit 3d4c26b16a04a084fe0bde08ccdd8086570f8bbe
	Issue introduced in 4.12 with commit eff484e0298da5a4d18ca82f5454c557fd942af5 and fixed in 7.2.5 with commit 36df368861d2664291298feeb37dfef43fcae670
	Issue introduced in 4.12 with commit eff484e0298da5a4d18ca82f5454c557fd942af5 and fixed in 7.3-rc1 with commit c6c156d931c33b92362383cf76f6d6e1291dcbfe

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-2026-89912
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/arm64/kvm/vgic/vgic-its.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/3d4c26b16a04a084fe0bde08ccdd8086570f8bbe
	https://git.kernel.org/stable/c/36df368861d2664291298feeb37dfef43fcae670
	https://git.kernel.org/stable/c/c6c156d931c33b92362383cf76f6d6e1291dcbfe