CVE-2026-93232
UnknownSummary
A vulnerability in the Linux kernel causes a boot panic on CONFIG_DEBUG_VM kernels when hugetlb_free_vmemmap is enabled. The issue is due to late initialization of shared tail pages (zone->vmemmap_tails[]) used by HVO, leading to dereferencing an uninitialized page during bootmem HugeTLB folio preparation. The fix moves initialization to gather_bootmem_prealloc() before bootmem HugeTLB folios are processed.
Risk Assessment
The risk affects systems with CONFIG_DEBUG_VM and hugetlb_free_vmemmap enabled, where a kernel panic during boot can prevent system startup. An attacker cannot directly exploit this, but a denial of service (DoS) may occur in environments using HugeTLB pages.
Recommendation
Update the Linux kernel to a version containing the fix (commit 622026e87c40 and related changes). If updating is not possible, temporarily disable hugetlb_free_vmemmap or CONFIG_DEBUG_VM in the kernel configuration.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: fix boot panic with CONFIG_DEBUG_VM and HVO bootmem pages Patch series "mm: Refactor bootmem gigantic hugepage allocation", v4. This series is split out from the earlier larger series "mm: Generalize HVO for HugeTLB and device DAX" [1]. It collects the first 19 patches of that series as a standalone set of fixes and preparatory cleanups around bootmem HugeTLB handling, sparse initialization ordering, and related vmemmap setup. The first patches fix a few bugs found while reviewing the existing code, including incorrect bootmem HVO handling, wrong vmemmap registration arguments, a powerpc compound-vmemmap tracking bug, and too-late initialization of gigantic bootmem HugeTLB struct pages. The rest of the series reorders early memory initialization so the relevant zone state is available before sparse and HugeTLB boot-time setup runs, then simplifies the remaining bootmem gigantic hugepage allocation path and removes code made obsolete by that rework. At a high level: - patches [1-4] fix boot-time and arch-specific bugs - patches [5-12] reorder and simplify sparse/mm/hugetlb early init - patches [13-19] refactor bootmem gigantic hugepage allocation and remove obsolete helpers and state This patch (of 19): Commit 622026e87c40 ("mm/hugetlb: remove fake head pages") switched HVO to reuse per-zone shared tail pages from zone->vmemmap_tails[]. Those shared tail pages were initialized in hugetlb_vmemmap_init(), but bootmem HugeTLB folios are prepared earlier from gather_bootmem_prealloc(). With hugetlb_free_vmemmap=on, prep_and_add_bootmem_folios() can access pageblock flags on bootmem HugeTLB pages whose mirrored tail struct pages already point to the shared tail page. On CONFIG_DEBUG_VM kernels, get_pfnblock_bitmap_bitidx() then dereferences the still-uninitialized shared tail page and can panic during boot. Initialize zone->vmemmap_tails[] from gather_bootmem_prealloc(), before bootmem HugeTLB folios are processed, and drop the later initialization from hugetlb_vmemmap_init(). This bug only affects CONFIG_DEBUG_VM kernels, where the relevant assertion is evaluated.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS