[CVE-2026-64507][MODERATE REGULAR] x86/bugs: Enable IBPB flush on BPF JIT allocation

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

CVE: CVE-2026-64507
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: x86/bugs: Enable IBPB flush on BPF JIT allocation
Commit: cb27f3bf915cc0f20fc0c48da9059304e39ebd35
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cb27f3bf915cc0f20fc0c48da9059304e39ebd35
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64507
Analysis date: Sat, 25 Jul 2026 13:26:09 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
BPF JIT memory reuse may leave branch predictor state useful for Spectre-v2 style JIT spraying, creating a local speculative information disclosure risk when BPF JIT is enabled and reachable by the attacker.

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

The original Linux kernel CVE announcement for CVE-2026-64507 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64507

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64507	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:N/A:N';CWE-203;*CWE-200;CWE-1303;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR 'BPF JIT memory reuse may leave branch predictor state in a form that can help Spectre-v2 style JIT spraying attacks. This is a local speculative execution information disclosure risk rather than a memory corruption or crash bug. For the CVSS the PR:L value is used because a local user or process that can cause BPF JIT allocations or reuse may be enough in some deployments, even though many systems restrict eBPF loading to privileged users. The issue is not directly network reachable and depends on BPF JIT being enabled, CPU predictor behavior, Spectre-v2 mitigation mode, and an observable side channel. Impact is confidentiality loss only, with no evidence of direct integrity impact or denial of service.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	INIT WARNONLY BPF LEAK SPECTRE HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Confidentiality impact plausible: +1. This is Spectre-v2 / JIT spraying hardening and the plausible impact is speculative side-channel information disclosure.
* Broad/default/common subsystem: +1. BPF JIT and Spectre-v2 mitigations are relevant on common x86 deployments, but exposure depends on BPF JIT being enabled.
* Requires admin/root/CAP_* in typical deployments: -2. In many hardened enterprise/product configurations, unprivileged BPF is disabled and BPF program loading is gated by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, or root-controlled policy.
* No memory corruption bonus. The patch does not show UAF, OOB write, double free, refcount abuse, type confusion, or arbitrary write.
* No reliable DoS bonus. The patch addresses predictor-state hardening, not a crash or stall.

Paranoid signals:

* Local unprivileged trigger: +1. In less restricted deployments, local users may be able to trigger BPF JIT allocation or reuse through permitted BPF paths.
* Local unprivileged high-control kernel data-plane API refinement: +1. BPF is a rich kernel data-plane API if reachable by unprivileged users in the evaluated configuration.
* Confidentiality impact plausible: +1. The risk class is information disclosure through speculative execution behavior.
* Broad/default/common subsystem: +1. x86 Spectre-v2 mitigation paths and BPF JIT are common enough to justify manual review when the product configuration allows BPF JIT exposure.

Call-site confidence: medium. The patch shows the mitigation being wired through bpf_arch_pred_flush via static_call_update and static_branch_enable, but the exact BPF JIT allocation/reuse call sites are not included in the provided diff.

## 3. Reachability analysis

The issue is local, not network reachable. Realistic triggering requires BPF JIT to be enabled and an attacker or local process to cause BPF JIT memory allocation or reuse under a Spectre-v2 mitigation mode where IBPB is needed. In conservative product configurations where unprivileged BPF is disabled, the attacker normally needs privileged BPF access, so the practical score is low. In permissive configurations with unprivileged BPF or other reachable BPF JIT paths, the issue becomes more actionable because a local user may be able to shape JIT activity and attempt a side-channel attack.

Namespaces and containers matter only if they provide meaningful BPF access without full host-root equivalence. If BPF loading remains host-root or CAP-gated, the full privilege penalty should apply.

## 4. Severity interpretation

This behaves more like a low-to-borderline Moderate hardening issue than an Important memory-corruption vulnerability. The theoretical impact is confidentiality loss through speculative execution side channels. The patch does not support integrity impact, availability impact, privilege escalation, or a concrete memory-corruption primitive. The paranoid score is higher only for configurations where local unprivileged BPF JIT interaction is realistically available.

## 5. One-sentence report phrase

BPF JIT memory reuse may leave branch predictor state useful for Spectre-v2 style JIT spraying, creating a local speculative information disclosure risk when BPF JIT is enabled and reachable by the attacker.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because exposure depends strongly on product-specific BPF policy, unprivileged BPF availability, CPU mitigation mode, and whether BPF JIT allocation or reuse is reachable by non-root users.

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

Patch: x86/bugs: Enable IBPB flush on BPF JIT allocation
Commit: cb27f3bf915cc0f20fc0c48da9059304e39ebd35
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cb27f3bf915cc0f20fc0c48da9059304e39ebd35

Commit description:

Enable hardening against JIT spraying when Spectre-v2 mitigations are in
use. Specifically, issue an IBPB flush on BPF JIT memory reuse. Skip
enabling the IBPB flush if the BPF dispatcher is already using a retpoline
sequence.

This hardening applies only when BPF-JIT is in use. Guard the enabling
under CONFIG_BPF_JIT so that bugs.c still builds with CONFIG_BPF_JIT=n.

  [ pawan: Use entry_ibpb() instead of write_ibpb(). JIT hardening enable
	   moved to spectre_v2_select_mitigation() because there is no
	   spectre_v2_apply_mitigation()]

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  arch/x86/include/asm/nospec-branch.h
  arch/x86/kernel/cpu/bugs.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=cb27f3bf915cc0f20fc0c48da9059304e39ebd35

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

The original Linux kernel CVE announcement for CVE-2026-64507 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64507

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:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
  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: 1
  Paranoid ActionableScore: 4

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).