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CVE-2025-21851 is a Linux kernel eBPF arena-map free-path vulnerability affecting AArch64 kernels configured with 64 KB pages. The arena_map_free() function passes the kernel virtual-memory start address returned by bpf_arena_get_kern_vm_start() to apply_to_existing_page_range(). When that address is not page-aligned, processing can reach apply_to_pte_range() with an unaligned address. This condition causes a segmentation fault and soft lockup during arena hash-table operations. The defect is not reported on AArch64 systems using 4 KB pages.
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Linux kernel BPF arena-map free-path soft-lockup condition on 64K-page kernels.
Linux kernel BPF arena free soft-lockup flaw.
A Linux kernel BPF arena-map flaw on AArch64 systems using 64 KB pages. An unaligned address passed by arena_map_free() to apply_to_existing_page_range() can reach apply_to_pte_range() and cause a segmentation fault and soft lockup. The fix rounds GUARD_SZ to twice PAGE_SIZE so bpf_arena_get_kern_vm_start() returns a page-aligned address.
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