[CVE-2026-72286][MODERATE 7.0] KVM: SEV: Do not allow intra-host migration/mirroring of SNP VMs

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-72286
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: KVM: SEV: Do not allow intra-host migration/mirroring of SNP VMs
Commit: b70404b89daad5f9f33f7ac640b1065cba639935
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b70404b89daad5f9f33f7ac640b1065cba639935
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72286
Analysis date: Sun, 16 Aug 2026 08:51:23 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
KVM allowed SEV-SNP encrypted context move or mirror operations without transferring required SNP-specific state, which can leave the destination VM in an inconsistent encrypted context and may affect availability or SEV-SNP isolation assumptions in local KVM control-plane scenarios.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-72286 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72286

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-72286	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-665;CWE-754;CWE-703;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.6';DESCR 'KVM allowed encrypted context move or mirror operations from a SEV-SNP source VM even though SNP specific state was not transferred or initialized on the destination. The missing state includes guest_req_mutex, guest_req_buf, guest_resp_buf, and VMSA feature information, which can leave the destination VM in an inconsistent encrypted context. For the CVSS the PR:L is used for the paranoid score because a local VMM process or user with access to KVM VM file descriptors can trigger these ioctls without being full host root in many deployments. The issue is not directly network reachable and requires local control plane access to KVM. Impact is at least guest or KVM availability degradation, and in the worst still defensible interpretation may affect confidentiality or integrity boundaries of SEV-SNP state due to inconsistent ASID and VM type handling.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	VIRT SIMPLEFIX HARDWARE  INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged or low-privileged trigger: +1
  A local VMM process or user with access to KVM VM file descriptors can invoke the SEV encrypted-context move or copy ioctls. This is not remote, but it does not necessarily require full host root in common KVM group or delegated virtualization setups.

* Privileged kernel or device-management state corruption path: +1
  The bug affects KVM SEV-SNP confidential-computing state, including SNP-specific guest request buffers, response buffers, VMSA feature state, and ASID classification.

* Availability impact realistic: +1
  Incomplete SNP state transfer can leave the destination VM in an inconsistent encrypted context, plausibly causing VM failure, KVM errors, or host-side instability in the affected path.

Paranoid-only signals:

* Confidentiality impact plausible: +1
  The affected state belongs to SEV-SNP isolation and encrypted VM context handling. The patch does not prove a disclosure primitive, but inconsistent SNP versus SEV classification can plausibly affect confidential-computing boundaries.

* Integrity impact plausible: +1
  The ASID and VMSA state mismatch may cause incorrect handling of encrypted guest state. This supports a limited integrity concern in the paranoid interpretation.

Subtract or limiting factors:

* No remote reachability: +0
  This requires local KVM control-plane access.

* No concrete memory corruption primitive: +0
  The patch does not show UAF, OOB write, double free, stale callback, arbitrary write, or attacker-controlled reclaim.

* Non-default specialized configuration: limiting factor
  The affected path requires SEV-SNP and intra-host migration or mirroring. This keeps the conservative score lower and prevents treating it as a broad default KVM issue.

* Validation-only cap applied
  The patch mainly rejects an unsupported configuration with EINVAL. Since no concrete downstream primitive is shown, conservative scoring stays below Important-class. Paranoid scoring is capped at 5.

## 3. Reachability analysis

The bug is reachable by a local process that can create or control KVM SEV-SNP VMs and pass a source VM fd into the encrypted context move or copy path. In typical deployments this is a VMM such as QEMU or a virtualization management service. It is not network-triggerable by packet traffic.

Namespaces and containers may matter if a reduced-privilege service, container root, or VM-management account has access to `/dev/kvm` and relevant VM file descriptors. That is why PR:L is the better paranoid interpretation than PR:H. However, ordinary unprivileged local users without KVM access cannot usually trigger this path.

The path is not default for all KVM users. It depends on AMD SEV-SNP support and use of intra-host migration or mirroring operations.

## 4. Severity interpretation

This is not a demonstrated memory-corruption bug. It is best classified as an incomplete state-transfer or improper validation issue in a security-sensitive KVM SEV-SNP path.

Realistically, the most supported impact is VM or KVM availability degradation due to inconsistent encrypted VM state. The paranoid concern is that incorrect SNP versus SEV state handling, ASID binding, and missing VMSA feature transfer could affect confidential-computing isolation assumptions. That makes it more than an ordinary Low issue, but not a Strong Important candidate without additional evidence of memory corruption, guest-to-host escape, or concrete confidentiality breach.

## 5. One-sentence report phrase

KVM allowed SEV-SNP encrypted context move or mirror operations without transferring required SNP-specific state, which can leave the destination VM in an inconsistent encrypted context and may affect availability or SEV-SNP isolation assumptions in local KVM control-plane scenarios.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch affects KVM confidential VM state, ASID classification, and SEV-SNP isolation-sensitive metadata. No concrete memory corruption primitive is shown, but the security boundary is important enough that this should not be auto-closed based only on the small validation diff.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: KVM: SEV: Do not allow intra-host migration/mirroring of SNP VMs
Commit: b70404b89daad5f9f33f7ac640b1065cba639935
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b70404b89daad5f9f33f7ac640b1065cba639935

Commit description:

The intra-host migration/mirroring feature is not fully implemented for
SEV-SNP VMs. The proper migration requires additional SNP-specific
state such as guest_req_mutex, guest_req_buf, and guest_resp_buf to be
transferred or initialized on the destination.

The SNP VM mirroring requires vmsa features to be copied as well otherwise
ASID would be bound to SNP range while VM is detected as a SEV VM.

Reject SNP source VMs in migration/mirroring until proper SNP state
transfer is implemented.

Fixes: 1dfe571 ("KVM: SEV: Add initial SEV-SNP support")

Reported-by: Chris Mason <clm@meta.com>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Atish Patra <atishp@meta.com>
Link: https://patch.msgid.link/20260602-sev_snp_fixes-v3-1-24bfd3ae047c@meta.com
Cc: stable@vger.kernel.org
[sean: let lines poke past 80 chars, tag for stable]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/x86/kvm/svm/sev.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b70404b89daad5f9f33f7ac640b1065cba639935

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-72286 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72286

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 3
  Paranoid ActionableScore: 5

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).