CVE-2026-68081: KVM: nVMX: Put vmcs12 pages if nested VM-Enter fails due to invalid guest state

CVE-2026-68081: KVM: nVMX: Put vmcs12 pages if nested VM-Enter fails due to invalid guest state

[Greg Kroah-Hartman]

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

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

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

KVM: nVMX: Put vmcs12 pages if nested VM-Enter fails due to invalid guest state

Put all vmcs12 pages if KVM synthesizes a nested VM-Exit due to invalid
guest while emulating VMLAUNCH or VMRESUME.  The invalid guest state path
doesn't use nested_vmx_vmexit() as that API is intended to be used if and
only if L2 is active, and the open coded equivalent neglects to put the
vmcs12 pages.  Failure to put the vmcs12 pages leaks any pinned pages
(and/or mappings) if L1 retries VMLAUNCH/VMRESUME.

Note, the !from_vmenter scenario doesn't suffer the same problem, as
vmx_get_nested_state_pages() only gets/pins/maps the vmcs12 pages if L2 is
active, i.e. if a "full" VM-Exit is guaranteed before KVM will retry
getting vmcs12 pages.

The Linux kernel CVE team has assigned CVE-2026-68081 to this issue.


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

	Issue introduced in 5.2 with commit 96c66e87deeeb3cc78a3b82a1de8e365eec206c1 and fixed in 6.18.40 with commit 7996013b85687034d2e820cef94d6404192e3a3d
	Issue introduced in 5.2 with commit 96c66e87deeeb3cc78a3b82a1de8e365eec206c1 and fixed in 7.1.5 with commit 2c87a087c20632d68920272173b5d7c47f9bcf70
	Issue introduced in 5.2 with commit 96c66e87deeeb3cc78a3b82a1de8e365eec206c1 and fixed in 7.2-rc4 with commit 2f2312c422fd2695da772cecb30c69994b795964

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-2026-68081
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/x86/kvm/vmx/nested.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/7996013b85687034d2e820cef94d6404192e3a3d
	https://git.kernel.org/stable/c/2c87a087c20632d68920272173b5d7c47f9bcf70
	https://git.kernel.org/stable/c/2f2312c422fd2695da772cecb30c69994b795964