CVE-2026-89930: KVM: nVMX: Service local TLB flushes on failed nested VM-Enter

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

KVM: nVMX: Service local TLB flushes on failed nested VM-Enter

KVM services local TLB flushes on "full" nested VM-Exits (through
__nested_vmx_vmexit()), but not if a nested VM-Enter fails (e.g. due to
failed VMCS checks in nested_vmx_enter_non_root_mode()).

However, it is possible that KVM had queued TLB flushes that need to be
performed, even if the nested VM-Enter was not successful. For example,
if VPID is disabled for L2 (via nested_vmx_transition_tlb_flush(), or if
via the MSR load lists, as the SDM says:

  If any MSR is being loaded in such a way that would architecturally
  require a TLB flush, the TLBs are updated so that, after VM entry, the
  logical processor will not use any translations that were cached before
  the transition.

The SDM is unclear about when the TLB flush should occur, and whether or
not a failed VM entry would flush the TLB, so it is safer to always
do the TLB flush in this case.

More concretely, KVM also updates the last VPID L1 used for L2 in
nested_vmx_transition_tlb_flush() (i.e. last_vpid), even if the VM entry
ultimately fails. With the current code, KVM could miss a TLB flush if
L1 changes L2's VPID, then does a failed VM entry followed by a
successful one, as the failed VM entry would update last_vpid but not
actually flush the TLB. Servicing local TLB flushes on failed VM entries
makes sure that the TLB is always flushed when last_vpid is updated.

The Linux kernel CVE team has assigned CVE-2026-89930 to this issue.


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

	Issue introduced in 4.4 with commit 5c614b3583e7b6dab0c86356fa36c2bcbb8322a0 and fixed in 5.15.221 with commit c0c66cd575e31218da6a7d104c6ef80b0830b60c
	Issue introduced in 4.4 with commit 5c614b3583e7b6dab0c86356fa36c2bcbb8322a0 and fixed in 6.1.188 with commit 1025b938dc439b75c720a568a855a13eeb245686
	Issue introduced in 4.4 with commit 5c614b3583e7b6dab0c86356fa36c2bcbb8322a0 and fixed in 6.6.157 with commit 312cdb6d8940827dea63a7a52fb714a5049f06d1
	Issue introduced in 4.4 with commit 5c614b3583e7b6dab0c86356fa36c2bcbb8322a0 and fixed in 6.12.110 with commit f74fccdf4f7fb0780cd84944108d35f3d9dc46a7
	Issue introduced in 4.4 with commit 5c614b3583e7b6dab0c86356fa36c2bcbb8322a0 and fixed in 6.18.51 with commit c43563e7518e65ec6ccaa6a65f84c5af5ca5d379
	Issue introduced in 4.4 with commit 5c614b3583e7b6dab0c86356fa36c2bcbb8322a0 and fixed in 7.2.5 with commit 62c3ee4c9f0e2efef5157358b3549e50ede96d73
	Issue introduced in 4.4 with commit 5c614b3583e7b6dab0c86356fa36c2bcbb8322a0 and fixed in 7.3-rc1 with commit 05a0b701d1089fb57beeb8982f23c3bbafe0fa8b

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-2026-89930
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/c0c66cd575e31218da6a7d104c6ef80b0830b60c
	https://git.kernel.org/stable/c/1025b938dc439b75c720a568a855a13eeb245686
	https://git.kernel.org/stable/c/312cdb6d8940827dea63a7a52fb714a5049f06d1
	https://git.kernel.org/stable/c/f74fccdf4f7fb0780cd84944108d35f3d9dc46a7
	https://git.kernel.org/stable/c/c43563e7518e65ec6ccaa6a65f84c5af5ca5d379
	https://git.kernel.org/stable/c/62c3ee4c9f0e2efef5157358b3549e50ede96d73
	https://git.kernel.org/stable/c/05a0b701d1089fb57beeb8982f23c3bbafe0fa8b