[CVE-2025-37960][LOW] memblock: Accept allocated memory before use in memblock_double_array()

[CVE-2025-37960][LOW] memblock: Accept allocated memory before use in memblock_double_array()

[AL-KERNEL]

CVE: CVE-2025-37960
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: memblock: Accept allocated memory before use in memblock_double_array()
Commit: d66a22f6a432a9dd376c9b365d7dc89bd416909c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d66a22f6a432a9dd376c9b365d7dc89bd416909c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37960
Analysis date: Mon, 12 Oct 2026 20:58:51 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2025-37960 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37960

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: LOW
Manual review required: NO

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

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2025-37960	LOW	https://www.kernelcve.org/list/?q=CVE-2025-37960 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_LOW_ELIGIBLE_NO_POSITIVE_SIGNAL (independent Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-754;CWE-908;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'During early boot memblock_find_in_range can return a physical range that has not yet been accepted by an AMD SEV SNP guest. memblock_double_array then converts that range to a virtual address and memcpy accesses inaccessible private memory, causing a guest kernel crash and preventing the virtual machine from booting. The demonstrated primitive is an invalid access to unaccepted memory rather than a UAF, OOB write, or arbitrary write. For the CVSS the PR:L value in the paranoid score reflects environments where a reduced capability cloud or virtualization account can start or reconfigure an SNP guest without having unrestricted host root access. Reliable triggering still requires a specific early boot memory layout and array growth condition, so AC:H is appropriate. The issue is not network reachable. Impact is denial of service to the affected guest with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	DANGER BOOT MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash / strong DoS. The supplied trace establishes a guest-kernel crash during early boot when `memcpy()` accesses an unaccepted SNP memory range.
* +0 Additional availability. Not awarded because failure to boot is the same consequence already counted as the crash.
* +0 Memory corruption. The destination is allocated for the enlarged memblock array but has not been accepted. This is not a confirmed heap OOB write, UAF, arbitrary write, or stale-object operation.
* +0 B5-R. No retry-accumulated index, repeated overwrite, attacker-influenced retry sequence, or later consumption of corrupted structured state is present.
* +0 Attacker reachability. No network, ordinary local-user, guest-runtime, or delegated-management operation is shown to force the vulnerable allocation.
* +0 Authorization impact. No authorization decision or protected resource is involved.
* No privilege penalty was applied because host-administrator control is not positively established as a necessary attacker prerequisite.
* No uncommon-hardware penalty was applied because SNP is a prerequisite but the evidence does not justify treating it as rare physical-only attacker access.

3. Reachability analysis

The failure occurs while an AMD SEV-SNP guest is booting, before normal userspace and namespace interfaces exist. An SNP-capable platform, unaccepted guest memory, pre-slab memblock array growth, and selection of that memory range are required.

The evidence does not establish that malicious guest code can trigger the condition after boot or that a cloud tenant can reliably force the relevant early-boot allocation. A host administrator or VMM may influence guest configuration and memory layout, but the supplied material does not establish the complete attacker-controlled sequence. Therefore `HostAdminRequired=UNKNOWN`.

The path is not namespace-scoped and has no direct network trigger. It is not a race, and no repeated attacker-controlled attempts against a running kernel are demonstrated.

4. Primitive and severity interpretation

The exact primitive is an invalid access to allocated but unaccepted SNP guest memory. `memblock_double_array()` converts the physical range with `__va()` and uses it as the destination for copying the enlarged array before the range has been accepted.

This is neither active structured stale state nor fixed post-lifetime storage. No object lifetime ends, no dangling reference exists, and no repeated release or refcount mutation occurs.

The demonstrated consequence is a guest-kernel crash and boot failure. There is no confirmed OOB write, corrupted-state consumption, disclosure, protected-state modification, host corruption, authorization bypass, or privilege escalation. The appropriate classification is `CLASS_C`.

`ImportantCandidate=NO` because no Important-preserving corruption, ownership, lifetime, semantic reinterpretation, or security-boundary primitive is established. `AutoDowngradeAllowed=YES` because the evidence supports a configuration-dependent boot-time DoS without unresolved exploitation leverage.

5. One-sentence report phrase

An SNP guest may crash during early boot because memblock array expansion can access an allocated physical range before that memory has been accepted.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch and trace establish a boot-time invalid-memory access and guest DoS, but no attacker-useful corruption, lifetime violation, authorization bypass, or cross-boundary primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: memblock: Accept allocated memory before use in memblock_double_array()
Commit: d66a22f6a432a9dd376c9b365d7dc89bd416909c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d66a22f6a432a9dd376c9b365d7dc89bd416909c

Commit description:

When increasing the array size in memblock_double_array() and the slab
is not yet available, a call to memblock_find_in_range() is used to
reserve/allocate memory. However, the range returned may not have been
accepted, which can result in a crash when booting an SNP guest:

  RIP: 0010:memcpy_orig+0x68/0x130
  Code: ...
  RSP: 0000:ffffffff9cc03ce8 EFLAGS: 00010006
  RAX: ff11001ff83e5000 RBX: 0000000000000000 RCX: fffffffffffff000
  RDX: 0000000000000bc0 RSI: ffffffff9dba8860 RDI: ff11001ff83e5c00
  RBP: 0000000000002000 R08: 0000000000000000 R09: 0000000000002000
  R10: 000000207fffe000 R11: 0000040000000000 R12: ffffffff9d06ef78
  R13: ff11001ff83e5000 R14: ffffffff9dba7c60 R15: 0000000000000c00
  memblock_double_array+0xff/0x310
  memblock_add_range+0x1fb/0x2f0
  memblock_reserve+0x4f/0xa0
  memblock_alloc_range_nid+0xac/0x130
  memblock_alloc_internal+0x53/0xc0
  memblock_alloc_try_nid+0x3d/0xa0
  swiotlb_init_remap+0x149/0x2f0
  mem_init+0xb/0xb0
  mm_core_init+0x8f/0x350
  start_kernel+0x17e/0x5d0
  x86_64_start_reservations+0x14/0x30
  x86_64_start_kernel+0x92/0xa0
  secondary_startup_64_no_verify+0x194/0x19b

Mitigate this by calling accept_memory() on the memory range returned
before the slab is available.

Prior to v6.12, the accept_memory() interface used a 'start' and 'end'
parameter instead of 'start' and 'size', therefore the accept_memory()
call must be adjusted to specify 'start + size' for 'end' when applying
to kernels prior to v6.12.

Cc: stable@vger.kernel.org # see patch description, needs adjustments for <= 6.11
Fixes: dcdfdd4 ("mm: Add support for unaccepted memory")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/da1ac73bf4ded761e21b4e4bb5178382a580cd73.1746725050.git.thomas.lendacky@amd.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/memblock.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=d66a22f6a432a9dd376c9b365d7dc89bd416909c

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

The original Linux kernel CVE announcement for CVE-2025-37960 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-37960

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:H/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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).