* [CVE-2026-81016][MODERATE REGULAR] platform/x86/amd/pmc: Propagate SMU errors and validate S2D address
@ 2026-09-12 8:53 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 8:53 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-81016
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: platform/x86/amd/pmc: Propagate SMU errors and validate S2D address
Commit: 8178f59d76570b152d836bde07f5997f15861f04
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8178f59d76570b152d836bde07f5997f15861f04
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81016
Analysis date: Sat, 12 Sep 2026 04:53:36 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-81016 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81016
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 REGULAR
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-81016 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-81016 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:L/I:L/A:H';CWE-252;*CWE-457;CWE-908;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'amd_pmc S2D initialization ignored SMU command failures while reading S2D_PHYS_ADDR_LOW/IMPORTANT, so phys_addr_low and phys_addr_hi could remain uninitialized and be passed to devm_ioremap(). If the failed query leaves the address as zero this can attempt to ioremap physical address 0 and trigger an ioremap on RAM warning. If stale stack values are used, the driver may attempt to map an unintended physical address, so the conservative impact is more than a pure warning and should be manually reviewed. For the CVSS the PR:L is used for the paranoid score because a reduced capability root, service account, or delegated platform management role might trigger driver initialization or recovery without full host administration. The issue is not network reachable and exploitation depends on AMD PMC hardware, SMU behavior, and the S2D feature path. Impact is at least local denial of service or warning driven disruption, with possible limited confidentiality or integrity impact from unintended physical address mapping.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES OOB NOMEMCHK ERRORPATH HARDWARE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
Conservative signals:
* +1 Weak or indirect corruption candidate. The patch shows uninitialized `phys_addr_low` and `phys_addr_hi` may be assembled into a physical address and passed to `devm_ioremap()`.
* +1 Firmware mediated external influence. The bad state is caused by SMU command failure or refusal, and firmware supplied or missing values materially affect the mapped address.
Paranoid additional signal:
* +1 Unresolved unintended physical mapping concern. If a nonzero stale value were used and `devm_ioremap()` succeeded, later STB access could potentially touch an unintended physical region. This is weak and unresolved, not a demonstrated read or write primitive.
Non-awarded signals:
* RealUAF not awarded. No stale post lifetime object use is shown.
* CLASS_A not awarded. No controlled reclaim, arbitrary write, controlled overwrite, callback control, COW violation, authorization bypass, or demonstrated LPE is established.
* CLASS_B not awarded. There is no concrete lifetime, refcount, RCU, or active object stale use primitive.
* Reliable kernel crash not awarded. The supplied evidence shows an `ioremap on RAM` warning, not a confirmed host panic or fatal crash.
* Confidentiality and integrity points not awarded. The patch does not establish a disclosure path or unauthorized modification path.
* Remote reachability not awarded. The issue is not packet or network triggered.
* Host admin penalty not applied. Host admin requirement is not fully proven from the supplied context, so it remains UNKNOWN rather than YES.
* Hardware rarity penalty not applied. AMD PMC and SMU involvement is hardware specific, but the evidence does not prove rare or physical only attacker requirements.
3. Reachability analysis
The vulnerable path is `amd_stb_s2d_init()` in the AMD PMC S2D initialization flow. The immediate trigger is failure of SMU commands used to query telemetry size and S2D physical address values.
A normal remote attacker cannot directly reach this path. There is no network input or packet processing path. Triggering appears tied to AMD platform firmware behavior, driver initialization, and possibly recovery or platform management operations.
The complete privilege boundary is unresolved. Driver initialization may happen automatically at boot, through device probing, or through privileged driver management. The supplied patch does not prove that an ordinary local user can trigger the complete vulnerable sequence. It also does not positively prove that host admin privilege is always required. Therefore `HostAdminRequired=UNKNOWN`.
Namespace scoped privilege is not relevant. There is no evidence that user namespaces, network namespaces, or namespace scoped capabilities can exercise this platform driver path. Therefore `NamespaceScopedPrivilege=NO`.
There is no race. There is no repeated lifetime operation. There is no known attacker controlled payload. Special AMD hardware and S2D feature support are prerequisites, but the evidence does not justify a strong rarity penalty.
4. Primitive and severity interpretation
The exact primitive is use of uninitialized physical address components after ignored SMU command failures. The assembled address is passed to `devm_ioremap()` before validating that the SMU address query succeeded and before rejecting zero.
This is not an active structured UAF and not fixed stale storage. It is an invalid state and unsafe physical mapping input issue. The demonstrated consequence is an `ioremap on RAM` warning when the address becomes zero. A stronger consequence would require showing that an unintended mapping can succeed and that later driver code exposes or modifies sensitive data through that mapping.
The primitive is classified as `CLASS_C` because the established behavior is primarily invalid state and warning driven disruption without an independently useful corruption primitive. The paranoid score keeps a manual review margin because physical address mapping bugs can hide stronger effects than the first visible warning, but the supplied evidence does not justify treating it as CLASS_A or CLASS_B.
`ImportantCandidate=NO` because there is no demonstrated memory corruption, UAF, authorization bypass, arbitrary read or write, or privilege escalation chain. `AutoDowngradeAllowed=YES` because the unresolved concern is weak and no concrete Important preserving primitive is established. Operationally this is a low to borderline Moderate platform driver robustness issue that deserves manual review, but not urgent Important classification from the supplied evidence alone.
5. One-sentence report phrase
AMD PMC S2D initialization ignored SMU command failures and could pass an uninitialized or zero physical address to devm_ioremap, causing an ioremap on RAM warning and possible local platform driver disruption, but no concrete UAF, arbitrary read or write, or privilege escalation primitive is established.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Manual review is recommended because an uninitialized physical address is used as an `ioremap()` input, and platform mapping bugs can sometimes have hidden consequences. The current evidence supports only weak unintended mapping concern and warning or disruption behavior.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: platform/x86/amd/pmc: Propagate SMU errors and validate S2D address
Commit: 8178f59d76570b152d836bde07f5997f15861f04
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8178f59d76570b152d836bde07f5997f15861f04
Commit description:
amd_stb_s2d_init() discards the return value of several S2D SMU commands.
When the SMU refuses a command (e.g. "SMU cmd failed. err: 0xff") the
failure is only noticed indirectly - if at all - and reported as -EIO,
masking the real error.
More seriously, the S2D_PHYS_ADDR_LOW/IMPORTANT return values are ignored, so
on failure phys_addr_low/hi are left uninitialised and the assembled
address is passed straight to devm_ioremap(). When the SMU leaves them at
zero this maps physical address 0 and trips the ioremap-on-RAM warning:
amd_pmc AMDI000B:00: SMU cmd failed. err: 0xff
ioremap on RAM at 0x0000000000000000 - 0x0000000000ffffff
WARNING: CPU: 13 PID: 4592 at arch/x86/mm/ioremap.c:...
Check the return value of each SMU command and propagate it, and reject a
zero physical address before calling devm_ioremap().
Reported-by: Francis De Brabandere <[email protected]>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221759
Tested-by: Francis De Brabandere <[email protected]>
Fixes: 3d7d407 ("platform/x86: amd-pmc: Add support for AMD Spill to DRAM STB feature")
Cc: [email protected]
Signed-off-by: Mario Limonciello <[email protected]>
Link: https://patch.msgid.link/[email protected]
Reviewed-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
arch/x86/mm/ioremap.c
drivers/platform/x86/amd/pmc/mp1_stb.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=8178f59d76570b152d836bde07f5997f15861f04
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-81016 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81016
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:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 5.8
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: 2
Paranoid ActionableScore: 3
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 REGULAR
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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