{"api_version":"1","generated_at":"2026-08-22T04:26:52+00:00","cve":"CVE-2026-72016","urls":{"html":"https://cve.report/CVE-2026-72016","api":"https://cve.report/api/cve/CVE-2026-72016.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-72016","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-72016"},"summary":{"title":"cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ncpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()\n\nOn arm64, when booting with `maxcpus` greater than the number of present\nCPUs (e.g., QEMU -smp cpus=4,maxcpus=8), some CPUs are marked as 'present'\nbut have not yet been registered via register_cpu(). Consequently,\nthe per-cpu device objects for these CPUs are not yet initialized.\n\nIn cpuhp_smt_enable(), the code iterates over all present CPUs. Calling\n_cpu_up() for these unregistered CPUs eventually leads to\nsysfs_create_group() being called with a NULL kobject (or a kobject\nwithout a directory), triggering the following warning in\nfs/sysfs/group.c:\n\n  WARNING: fs/sysfs/group.c:137 at internal_create_group+0x41c/0x4bc, CPU#2: sh/181\n  [...]\n  Call trace:\n    internal_create_group+0x41c/0x4bc (P)\n    sysfs_create_group+0x18/0x24\n    topology_add_dev+0x1c/0x28\n    cpuhp_invoke_callback+0x104/0x20c\n    __cpuhp_invoke_callback_range+0x94/0x11c\n    _cpu_up+0x200/0x37c\n\nWhen booting with ACPI, arm64 smp_prepare_cpus() currently sets all\nenumerated CPUs as \"present\" regardless of their status in the MADT. This\ncauses issues with SMT hotplug control. For instance, with QEMU's\n\"-smp 4,maxcpus=8\" configuration, the MADT GICC entries are populated as\nfollows:\n\n1. The first four CPUs: `Enabled` set but `Online Capable` not set.\n\n2. The remaining four CPUs: `Online Capable` set but `Enabled` not set\n   to support potential hot-plugging.\n\nFix this by:\n\n1. When booting with ACPI, checking the ACPI_MADT_ENABLED flag in the GICC\n   entry before calling set_cpu_present() during SMP initialization.\n\n2. Properly managing the present mask in acpi_map_cpu() and\n   acpi_unmap_cpu() to support actual CPU hotplug events, This aligns with\n   other architectures like x86 and LoongArch.\n\n3. Update the arm64 CPU hotplug documentation to no longer state that all\n   online-capable vCPUs are marked as present by the kernel at boot time.\n\nThis ensures that only physically available or explicitly enabled CPUs\nare in the present mask, keeping the SMT control logic consistent with\nthe actual hardware state.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-08-15 06:21:00","updated_at":"2026-08-17 06:17:59"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/f9a82544c7174851f5c7524622f5966dcafd3a47","name":"https://git.kernel.org/stable/c/f9a82544c7174851f5c7524622f5966dcafd3a47","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/901a489d89ee9c854624c8444090e38e70aed234","name":"https://git.kernel.org/stable/c/901a489d89ee9c854624c8444090e38e70aed234","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/ccdf1770a4ba27e31599d24ad970d77a371c7912","name":"https://git.kernel.org/stable/c/ccdf1770a4ba27e31599d24ad970d77a371c7912","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-72016","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-72016","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb ccdf1770a4ba27e31599d24ad970d77a371c7912 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb 901a489d89ee9c854624c8444090e38e70aed234 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb f9a82544c7174851f5c7524622f5966dcafd3a47 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.15","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.15 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.40 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1.5 7.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"72016","cve":"CVE-2026-72016","epss":"0.001980000","percentile":"0.099070000","score_date":"2026-08-17","updated_at":"2026-08-18 00:11:47"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["Documentation/arch/arm64/cpu-hotplug.rst","arch/arm64/kernel/acpi.c","arch/arm64/kernel/smp.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"ccdf1770a4ba27e31599d24ad970d77a371c7912","status":"affected","version":"eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb","versionType":"git"},{"lessThan":"901a489d89ee9c854624c8444090e38e70aed234","status":"affected","version":"eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb","versionType":"git"},{"lessThan":"f9a82544c7174851f5c7524622f5966dcafd3a47","status":"affected","version":"eed4583bcf9a60f8d6dd3a3c7c94dea28134b1eb","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["Documentation/arch/arm64/cpu-hotplug.rst","arch/arm64/kernel/acpi.c","arch/arm64/kernel/smp.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"6.15"},{"lessThan":"6.15","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.40","versionType":"semver"},{"lessThanOrEqual":"7.1.*","status":"unaffected","version":"7.1.5","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.2","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.40","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.5","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2","versionStartIncluding":"6.15","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ncpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()\n\nOn arm64, when booting with `maxcpus` greater than the number of present\nCPUs (e.g., QEMU -smp cpus=4,maxcpus=8), some CPUs are marked as 'present'\nbut have not yet been registered via register_cpu(). Consequently,\nthe per-cpu device objects for these CPUs are not yet initialized.\n\nIn cpuhp_smt_enable(), the code iterates over all present CPUs. Calling\n_cpu_up() for these unregistered CPUs eventually leads to\nsysfs_create_group() being called with a NULL kobject (or a kobject\nwithout a directory), triggering the following warning in\nfs/sysfs/group.c:\n\n  WARNING: fs/sysfs/group.c:137 at internal_create_group+0x41c/0x4bc, CPU#2: sh/181\n  [...]\n  Call trace:\n    internal_create_group+0x41c/0x4bc (P)\n    sysfs_create_group+0x18/0x24\n    topology_add_dev+0x1c/0x28\n    cpuhp_invoke_callback+0x104/0x20c\n    __cpuhp_invoke_callback_range+0x94/0x11c\n    _cpu_up+0x200/0x37c\n\nWhen booting with ACPI, arm64 smp_prepare_cpus() currently sets all\nenumerated CPUs as \"present\" regardless of their status in the MADT. This\ncauses issues with SMT hotplug control. For instance, with QEMU's\n\"-smp 4,maxcpus=8\" configuration, the MADT GICC entries are populated as\nfollows:\n\n1. The first four CPUs: `Enabled` set but `Online Capable` not set.\n\n2. The remaining four CPUs: `Online Capable` set but `Enabled` not set\n   to support potential hot-plugging.\n\nFix this by:\n\n1. When booting with ACPI, checking the ACPI_MADT_ENABLED flag in the GICC\n   entry before calling set_cpu_present() during SMP initialization.\n\n2. Properly managing the present mask in acpi_map_cpu() and\n   acpi_unmap_cpu() to support actual CPU hotplug events, This aligns with\n   other architectures like x86 and LoongArch.\n\n3. Update the arm64 CPU hotplug documentation to no longer state that all\n   online-capable vCPUs are marked as present by the kernel at boot time.\n\nThis ensures that only physically available or explicitly enabled CPUs\nare in the present mask, keeping the SMT control logic consistent with\nthe actual hardware state."}],"providerMetadata":{"dateUpdated":"2026-08-17T05:06:38.684Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/ccdf1770a4ba27e31599d24ad970d77a371c7912"},{"url":"https://git.kernel.org/stable/c/901a489d89ee9c854624c8444090e38e70aed234"},{"url":"https://git.kernel.org/stable/c/f9a82544c7174851f5c7524622f5966dcafd3a47"}],"title":"cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-72016","datePublished":"2026-08-15T05:51:44.050Z","dateReserved":"2026-08-09T03:40:39.900Z","dateUpdated":"2026-08-17T05:06:38.684Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-08-15 06:21:00","lastModifiedDate":"2026-08-17 06:17:59","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"72016","Ordinal":"1","Title":"cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()","CVE":"CVE-2026-72016","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"72016","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\ncpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()\n\nOn arm64, when booting with `maxcpus` greater than the number of present\nCPUs (e.g., QEMU -smp cpus=4,maxcpus=8), some CPUs are marked as 'present'\nbut have not yet been registered via register_cpu(). Consequently,\nthe per-cpu device objects for these CPUs are not yet initialized.\n\nIn cpuhp_smt_enable(), the code iterates over all present CPUs. Calling\n_cpu_up() for these unregistered CPUs eventually leads to\nsysfs_create_group() being called with a NULL kobject (or a kobject\nwithout a directory), triggering the following warning in\nfs/sysfs/group.c:\n\n  WARNING: fs/sysfs/group.c:137 at internal_create_group+0x41c/0x4bc, CPU#2: sh/181\n  [...]\n  Call trace:\n    internal_create_group+0x41c/0x4bc (P)\n    sysfs_create_group+0x18/0x24\n    topology_add_dev+0x1c/0x28\n    cpuhp_invoke_callback+0x104/0x20c\n    __cpuhp_invoke_callback_range+0x94/0x11c\n    _cpu_up+0x200/0x37c\n\nWhen booting with ACPI, arm64 smp_prepare_cpus() currently sets all\nenumerated CPUs as \"present\" regardless of their status in the MADT. This\ncauses issues with SMT hotplug control. For instance, with QEMU's\n\"-smp 4,maxcpus=8\" configuration, the MADT GICC entries are populated as\nfollows:\n\n1. The first four CPUs: `Enabled` set but `Online Capable` not set.\n\n2. The remaining four CPUs: `Online Capable` set but `Enabled` not set\n   to support potential hot-plugging.\n\nFix this by:\n\n1. When booting with ACPI, checking the ACPI_MADT_ENABLED flag in the GICC\n   entry before calling set_cpu_present() during SMP initialization.\n\n2. Properly managing the present mask in acpi_map_cpu() and\n   acpi_unmap_cpu() to support actual CPU hotplug events, This aligns with\n   other architectures like x86 and LoongArch.\n\n3. Update the arm64 CPU hotplug documentation to no longer state that all\n   online-capable vCPUs are marked as present by the kernel at boot time.\n\nThis ensures that only physically available or explicitly enabled CPUs\nare in the present mask, keeping the SMT control logic consistent with\nthe actual hardware state.","Type":"Description","Title":"cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable()"}]}}}