cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()
In the Linux kernel, the following vulnerability has been resolved: cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable() On arm64, when booting with `maxcpus` greater than the number of present CPUs (e.g., QEMU -smp cpus=4,maxcpus=8), some CPUs are marked as 'present' but have not yet been registered via register_cpu(). Consequently, the per-cpu device objects for these CPUs are not yet initialized. In cpuhp_smt_enable(), the code iterates over all present CPUs. Calling _cpu_up() for these unregistered CPUs eventually leads to sysfs_create_group() being called with a NULL kobject (or a kobject without a directory), triggering the following warning in fs/sysfs/group.c: WARNING: fs/sysfs/group.c:137 at internal_create_group+0x41c/0x4bc, CPU#2: sh/181 [...] Call trace: internal_create_group+0x41c/0x4bc (P) sysfs_create_group+0x18/0x24 topology_add_dev+0x1c/0x28 cpuhp_invoke_callback+0x104/0x20c __cpuhp_invoke_callback_range+0x94/0x11c _cpu_up+0x200/0x37c When booting with ACPI, arm64 smp_prepare_cpus() currently sets all enumerated CPUs as "present" regardless of their status in the MADT. This causes issues with SMT hotplug control. For instance, with QEMU's "-smp 4,maxcpus=8" configuration, the MADT GICC entries are populated as follows: 1. The first four CPUs: `Enabled` set but `Online Capable` not set. 2. The remaining four CPUs: `Online Capable` set but `Enabled` not set to support potential hot-plugging. Fix this by: 1. When booting with ACPI, checking the ACPI_MADT_ENABLED flag in the GICC entry before calling set_cpu_present() during SMP initialization. 2. Properly managing the present mask in acpi_map_cpu() and acpi_unmap_cpu() to support actual CPU hotplug events, This aligns with other architectures like x86 and LoongArch. 3. Update the arm64 CPU hotplug documentation to no longer state that all online-capable vCPUs are marked as present by the kernel at boot time. This ensures that only physically available or explicitly enabled CPUs are in the present mask, keeping the SMT control logic consistent with the actual hardware state.
- Published
- Aug 15, 2026
- Updated
- Aug 17, 2026
- EPSS
- 0.2% · 10th percentile
- CWE
- —
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Report tools
Action score
0
Monitor
Low priority for now.
- CVSS
- 0 / 40 · —
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.2%
Affected systems
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Versions reported by the vendor
Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.
Linux Linux
- 6.15affected
- eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb and later · before ccdf1770a4ba27e31599d24ad970d77a371c7912affected · git
- eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb and later · before 901a489d89ee9c854624c8444090e38e70aed234affected · git
- eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb and later · before f9a82544c7174851f5c7524622f5966dcafd3a47affected · git
- before 6.15not affected · semver
- 6.18.40 and later · up to and including 6.18.*not affected · semver
- 7.1.5 and later · up to and including 7.1.*not affected · semver
- 7.2 and laternot affected · original_commit_for_fix
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:14 | linux | before 7.1.5-1 | 7.1.5-1 |
Same product
linux: all recordsOther highest-scoring records for the same primary product.
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- CVE-2026-74309vdpa/octeon_ep: fix IRQ-to-ring mapping in interrupt handler40Plan
- CVE-2026-74280crypto: marvell/octeontx - fix DMA cleanup using wrong loop index40Plan
- CVE-2026-74279crypto: cavium/cpt - fix DMA cleanup using wrong loop index40Plan
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| Linux Linux | 901a489d89ee9c854624c8444090e38e70aed234 | Vendor (CNA) |
| Linux Linux | ccdf1770a4ba27e31599d24ad970d77a371c7912 | Vendor (CNA) |
| Linux Linux | f9a82544c7174851f5c7524622f5966dcafd3a47 | Vendor (CNA) |
| debian:linux | 7.1.5-1 · Debian:14 | Package registry (OSV) |
Exploit status
No known public exploit
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For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
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Weakness class (CWE)
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We use this product, ask for helpChange log
- Fix✗ → ✓
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References
- git.kernel.org/stable/c/901a489d89ee9c854624c8444090e38e70aed234
- git.kernel.org/stable/c/ccdf1770a4ba27e31599d24ad970d77a371c7912
- git.kernel.org/stable/c/f9a82544c7174851f5c7524622f5966dcafd3a47
Vendor advisories and official records. Exploit/PoC links are deliberately left out.