[CVE-2026-53277][IMPORTANT] KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation

[CVE-2026-53277][IMPORTANT] KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation

[AL-KERNEL]

CVE: CVE-2026-53277
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation
Commit: 97706097f9b851cfe55c3b00b083dfc2bcf542bc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=97706097f9b851cfe55c3b00b083dfc2bcf542bc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53277
Analysis date: Fri, 26 Jun 2026 03:42:19 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
Missing SRCU locking in KVM arm64 AT emulation and fault-injection page-table walks can race with memslot updates, potentially causing stale memory-translation state access, host kernel crash, and in the worst case UAF-like impact requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-53277 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53277

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: IMPORTANT
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-2026-53277	IMPORTANT	CHECK	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-667;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'Missing SRCU protection in KVM arm64 AT emulation and fault injection page table walks can race with memslot updates while walk_s1 or kvm_walk_nested_s2 is traversing memory translation state. This may expose the host kernel to stale memslot access, inconsistent page table walk results, or a use after free candidate if the protected memory slot state is replaced while the walk is in progress. For the CVSS the PR:L is used because reliable triggering normally requires a local user or VMM process with access to KVM ioctls and the ability to run vCPU activity while changing VM memory slots. The issue is not directly network reachable and is triggered through local virtualization control paths rather than packet traffic. Impact is at least local denial of service via host kernel crash, and in the paranoid case may include confidentiality or integrity impact because the bug class is a KVM race in memory translation state protected by SRCU.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-53277  SKIP The Fixes patch not applied yet, so unlikely that actual: 50f77dc87f133b09db44a5bbfdd64b1ca83a8d8e YES  NO NO unknown 	MAYBE	VIRT SIMPLEFIX HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local user or VMM process with access to `/dev/kvm` can potentially exercise the affected KVM arm64 paths.
* Memory corruption, weak or indirect corruption candidate: +1
  Missing SRCU protection can allow page-table or memslot walks to race with memslot changes, creating stale object access risk, but the patch does not show a demonstrated controlled overwrite primitive.
* Real lifetime corruption: +1
  SRCU is specifically required to protect memslot lifetime during walks, so missing SRCU is a real lifetime synchronization bug.
* Reliable kernel crash or strong DoS: +1
  A stale memslot or invalid walk state can plausibly crash the host kernel.
* Broad virtualization subsystem exposure: +1
  KVM is a common virtualization subsystem on arm64 systems that run VMs.
* Hard or unreliable race: -1
  Exploitation depends on racing page-table walks with memslot updates.

Conservative total: 5

Paranoid additional signals:

* Weak LPE concern: +1
  The affected path is in host kernel KVM memory translation logic, and stale memslot traversal may become more than a crash depending on object lifetime and reclaim behavior.
* Confidentiality impact plausible: +1
  In the paranoid interpretation, stale translation or object access could expose host or guest memory state.
* Integrity impact plausible: +1
  In the paranoid interpretation, stale translation state could affect memory access decisions or object interpretation.

Paranoid total: 7

## 3. Reachability analysis

The issue is local, not network reachable. Triggering requires access to KVM functionality, typically through `/dev/kvm`, plus the ability to run vCPU activity while changing VM memory slots. This is often available to local users in the `kvm` group or to virtualization service accounts, so PR:L is more appropriate than PR:H for practical triage. Containers or delegated virtualization environments may lower the effective privilege boundary further if KVM access is exposed inside the environment.

The bug is not default reachable on systems that do not run KVM guests or do not expose `/dev/kvm`. Realistic exploitation likely requires carefully timed interaction between AT emulation or fault-injection page-table walks and concurrent memslot updates.

## 4. Severity interpretation

This is more than an ordinary Moderate because it is a KVM host-kernel lifetime race in memory translation state. The conservative interpretation is Actionable Moderate: local KVM access plus a hard race can plausibly produce host kernel DoS. The paranoid interpretation is a Strong Important candidate because SRCU violations around memslot lifetime can hide stale pointer or UAF-style behavior, even if the patch itself does not demonstrate a controlled corruption primitive.

Theoretical memory corruption potential exists due to missing lifetime protection. Realistic exploitation evidence is limited to the locking violation and the known requirement that these walkers run under `kvm->srcu`.

## 5. One-sentence report phrase

Missing SRCU locking in KVM arm64 AT emulation and fault-injection page-table walks can race with memslot updates, potentially causing stale memory-translation state access, host kernel crash, and in the worst case UAF-like impact requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a KVM memory-lifetime race involving memslot-protected page-table walks. Even though the demonstrated impact is not a proven privilege-escalation primitive, SRCU lifetime bugs in KVM translation paths are high-risk enough to require manual review.

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

Patch: KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation
Commit: 97706097f9b851cfe55c3b00b083dfc2bcf542bc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=97706097f9b851cfe55c3b00b083dfc2bcf542bc

Commit description:

walk_s1() and kvm_walk_nested_s2() expect to be called while holding
kvm->srcu to guard against memslot changes. While this is generally
the case, __kvm_at_s12() and __kvm_find_s1_desc_level() call into the
respective walkers without taking kvm->srcu.

Fix by acquiring kvm->srcu prior to the table walk in both instances.

Cc: stable@vger.kernel.org
Fixes: 50f77dc ("KVM: arm64: Populate level on S1PTW SEA injection")
Fixes: be04ceb ("KVM: arm64: nv: Add emulation of AT S12E{0,1}{R,W}")
Suggested-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/aiAZfdeyanIvP8SD@v4bel
Signed-off-by: Marc Zyngier <maz@kernel.org>
[ Hyunwoo Kim: __kvm_at_s12() still returns void in 6.18.y, so the
  surrounding context differs from upstream (return; instead of
  return ret;); the added scoped_guard() is unchanged. ]
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/arm64/kvm/at.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=97706097f9b851cfe55c3b00b083dfc2bcf542bc

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

The original Linux kernel CVE announcement for CVE-2026-53277 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53277

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:N/I:N/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: 5
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).