[CVE-2026-72325][MODERATE REGULAR] perf/x86/amd/core: Avoid enabling BRS from the SVM reload path [ Upstream

[CVE-2026-72325][MODERATE REGULAR] perf/x86/amd/core: Avoid enabling BRS from the SVM reload path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72325
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: perf/x86/amd/core: Avoid enabling BRS from the SVM reload path [ Upstream
Commit: e9b1a7411a667539c2f55e720bbb5f623b526a32
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e9b1a7411a667539c2f55e720bbb5f623b526a32
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72325
Analysis date: Sun, 16 Aug 2026 08:20:44 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Borderline manual review recommended
Manual review required: YES

Summary:
A local denial of service is possible on affected AMD virtualization hosts when active LBR perf users cause the SVM reload path to incorrectly enable BRS and trigger a host kernel general protection fault.

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

The original Linux kernel CVE announcement for CVE-2026-72325 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72325

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-2026-72325	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:N/I:N/A:H';CWE-754;CWE-703;CWE-755;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A local denial of service can occur in the AMD perf and SVM interaction path when active LBR users cause the SVM reload path to call code that also enables BRS. On AMD systems that provide LBR but not BRS, this can make the kernel write the BRS enable bit in DebugExtnCfg MSR 0xc000010f and trigger a general protection fault in host kernel context. For the CVSS the PR:L value is used because a local user or service account with access to KVM or perf interfaces may be able to arrange active LBR events and trigger SVM virtualization reloads on affected AMD systems. The issue is not network reachable and requires local execution plus matching hardware and kernel configuration. Impact is denial of service via host crash or severe kernel fault. There is no evidence of a memory corruption primitive, information disclosure, or privilege escalation from this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline manual review recommended (with actual score 3)	YES	DANGER HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Borderline manual review recommended**::

## 2. Signal breakdown

Triggered signals:

* Local low privileged trigger: +1
  A local user or service account with access to KVM and perf related interfaces may be able to create active LBR users and cause SVM virtualization reload activity.

* Reliable kernel crash / strong DoS: +1
  The patch context shows a host kernel #GP caused by writing the BRS enable bit to DebugExtnCfg MSR 0xc000010f on hardware where that bit is unsupported or deprecated.

* Availability impact realistic: +1 in paranoid score only
  The failure occurs in host kernel context and can plausibly crash or severely destabilize the host, but this partially overlaps with the strong DoS signal, so it is only used for the higher score.

Subtracted signals:

* Hardware specific condition: -1 conservative, effectively limiting severity
  The issue requires AMD PerfMonV2 capable hardware with LBR but without usable BRS behavior, plus active LBR users and SVM reload activity.

Not triggered:

* No remote reachable / network trigger.
* No firmware mediated external influence.
* No UAF, double free, OOB write, type confusion, refcount abuse, arbitrary write, or page cache corruption.
* No plausible privilege escalation primitive from the patch.
* No confidentiality or integrity impact supported by the patch.

## 3. Reachability analysis

The bug is locally reachable only under specific host conditions. A realistic trigger requires affected AMD CPU features, active LBR perf users, and SVM/KVM virtualization state changes that invoke the reload path. Namespaces and containers do not by themselves make this broadly reachable, but delegated access to /dev/kvm or perf facilities can reduce the practical privilege barrier from full administrator to a local service or group member. The path is not network reachable and does not involve packet processing. Exploitation conditions are realistic on affected virtualization hosts, but not broadly default across all Linux systems.

## 4. Severity interpretation

This behaves like an ordinary Moderate local DoS rather than an Important class vulnerability. The demonstrated failure mode is a host kernel #GP caused by an invalid MSR write in the AMD perf and SVM interaction path. There is no evidence of memory lifetime corruption, attacker controlled overwrite, information disclosure, or privilege escalation. The paranoid score is slightly higher because the crash can occur in host kernel context on virtualization systems, but the hardware and configuration dependency prevents treating it as broadly actionable Important.

## 5. One-sentence report phrase

A local denial of service is possible on affected AMD virtualization hosts when active LBR perf users cause the SVM reload path to incorrectly enable BRS and trigger a host kernel general protection fault.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is useful to confirm affected AMD CPU exposure, perf access policy, and whether untrusted local users or service accounts can access KVM/perf on the evaluated product. It is not a strong Important candidate without additional evidence of memory corruption or privilege escalation.

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

Patch: perf/x86/amd/core: Avoid enabling BRS from the SVM reload path [ Upstream
Commit: e9b1a7411a667539c2f55e720bbb5f623b526a32
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e9b1a7411a667539c2f55e720bbb5f623b526a32

Changed files:
  arch/x86/events/amd/core.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=e9b1a7411a667539c2f55e720bbb5f623b526a32

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

The original Linux kernel CVE announcement for CVE-2026-72325 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72325

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).