[CVE-2026-74607][MODERATE 7.0] KVM: SVM: Serialize accesses to the owner and mirror list with separate lock

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

CVE: CVE-2026-74607
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: KVM: SVM: Serialize accesses to the owner and mirror list with separate lock
Commit: 47976eaaf0a4eb46dade48b3246779090db9e3ec
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=47976eaaf0a4eb46dade48b3246779090db9e3ec
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74607
Analysis date: Sat, 22 Aug 2026 16:04:25 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in KVM SVM SEV encrypted-context MOVE, COPY, and VM destroy paths can corrupt the SEV mirror VM list or release the wrong KVM object, causing at least host DoS and a plausible but unproven KVM object lifetime corruption risk.

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

The original Linux kernel CVE announcement for CVE-2026-74607 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74607

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-2026-74607	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in KVM SVM SEV encrypted context migration can occur when MOVE and COPY encrypted context operations or VM destruction run concurrently. The shared SEV mirror ownership fields enc_context_owner, mirror_vms, and mirror_entry were not consistently serialized, so a mirror entry could be moved while another path updates or destroys the same list. This can corrupt the mirror VM list or cause kvm_put_kvm to be applied to the wrong KVM object, creating a plausible lifetime bug and UAF candidate in host kernel memory. For the CVSS the PR:L is used because triggering requires local access to KVM and SEV ioctls rather than full host administrative privileges in many deployments. The issue is not directly network reachable and requires an AMD SEV capable KVM environment. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB LOCK VIRT RACE HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  Triggering is local through KVM VM ioctls. In many deployments access to `/dev/kvm` is delegated to non-root users or service accounts in the `kvm` group.

* Memory corruption, weak or indirect corruption candidate: +1
  The patch addresses list corruption in `mirror_vms` and inconsistent ownership in `enc_context_owner`. The primitive is real kernel state corruption, but the patch does not show attacker-controlled overwrite, reclaim, callback control, or arbitrary write.

* Real lifetime corruption: +1
  The wrong VM can receive `kvm_put_kvm()`, which is a concrete refcount and object-lifetime hazard.

* Reliable kernel crash / strong DoS: +1
  Corrupting a kernel list or releasing the wrong KVM object can realistically lead to host kernel crash or severe KVM instability.

* Hard or unreliable race / special timing required: -1
  The bug requires concurrent MOVE, COPY, or destroy operations hitting a narrow race window.

* Rare AND difficult-to-reach subsystem/configuration: -1
  The issue requires AMD SEV KVM support and the SEV encrypted-context mirror or migration feature, not just ordinary KVM execution.

Paranoid additions or interpretation:

* Weak LPE concern: +1
  Because the bug can corrupt KVM object ownership and refcount lifetime, privilege escalation is not demonstrated but is plausible enough for manual review. This raises the paranoid score to 5.

I would not award strong LPE +2 because the patch does not show attacker-controlled reclaim, object replacement, arbitrary write, callback dispatch, or a reliable type-confusion primitive.

## 3. Reachability analysis

The bug is not network reachable. It is reachable locally by a process that can create or control KVM VMs and use the SEV encrypted context MOVE and COPY ioctls. In typical desktop or virtualization-host deployments this may be available to non-root users in the `kvm` group, so PR:L is more appropriate than PR:H for practical triage. Containers usually do not get `/dev/kvm` and SEV access by default, but VM-management service accounts or reduced-privilege roots may have enough access. The affected path is configuration and hardware dependent because it requires AMD SEV and encrypted-context mirror or migration operations.

## 4. Severity interpretation

This is more than an ordinary Moderate correctness bug because it involves kernel list corruption and KVM object lifetime corruption. Realistic impact is likely host DoS or KVM crash due to corrupted mirror lists or incorrect `kvm_put_kvm()`. Theoretical escalation is plausible because incorrect object lifetime handling in KVM can become UAF-like host memory corruption, but the supplied patch does not demonstrate a controlled exploitation primitive. Therefore it fits **Actionable Moderate at minimum**, with manual review justified for possible Important classification.

## 5. One-sentence report phrase

A race in KVM SVM SEV encrypted-context MOVE, COPY, and VM destroy paths can corrupt the SEV mirror VM list or release the wrong KVM object, causing at least host DoS and a plausible but unproven KVM object lifetime corruption risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: concrete kernel list corruption and wrong KVM refcount release are present in a privileged virtualization subsystem, and although exploitation requires a race and SEV-specific setup, the lifetime-corruption nature makes it unsafe to auto-close.

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

Patch: KVM: SVM: Serialize accesses to the owner and mirror list with separate lock
Commit: 47976eaaf0a4eb46dade48b3246779090db9e3ec
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=47976eaaf0a4eb46dade48b3246779090db9e3ec

Commit description:

Interaction between KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM and
KVM_CAP_VM_COPY_ENC_CONTEXT_FROM can cause two separate issues:

- in sev_migrate_from(), when the destination KVM is a mirror, the mirror
  entry is moved from the source's list to the owner's mirror_vms list,
  without holding the owner's lock unlike other writers of the owner's
  mirror list (sev_vm_copy_enc_context_from(), sev_vm_destroy()).
  A concurrent COPY or destroy can race with sev_migrate_from() and
  corrupt the list.

- In sev_vm_destroy(), the *owner* is still active and could receive
  concurrently a KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM that causes
  sev->enc_context_owner to change.  In this case the incorrect VM
  receives kvm_put_kvm().

The second issue needs particular care because the owner could disappear
altogether (even though the race window is impossibly small) between
reading it and locking it.  There is thus no way to perform the checks
under the owner lock without putting struct kvm under SLAB_TYPESAFE_BY_RCU
(which would allow kvm_get_kvm_safe() under RCU critical section).

It is much simpler to just use a global lock, since the critical
sections are so small and the new lock is always a leaf lock.

Fixes: b212551 ("KVM: SEV: Allow SEV intra-host migration of VM with mirrors")
Cc: stable@vger.kernel.org
Reported-by: Shen Yongchao <grayhat@foxmail.com>
Link: https://lore.kernel.org/kvm/tencent_625C0F42824E542C72B34733392AF2C49709@qq.com/
Link: https://lore.kernel.org/kvm/tencent_DDC4E4352EC91CAC05A9A8F4E55E8C96730A@qq.com/
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

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=47976eaaf0a4eb46dade48b3246779090db9e3ec

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

The original Linux kernel CVE announcement for CVE-2026-74607 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74607

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:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 4
  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).