CVE-2025-21851: bpf: Fix softlockup in arena_map_free on 64k page kernel

Severity: low (CVSS 3.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-03-12 · updated 2026-07-30
Weakness: CWE-667

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix softlockup in arena_map_free on 64k page kernel On an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y, arena_htab tests cause a segmentation fault and soft lockup. The same failure is not observed with 4k pages on aarch64. It turns out arena_map_free() is calling apply_to_existing_page_range() with the address returned by bpf_arena_get_kern_vm_start(). If this address is not page-aligned the code ends up calling apply_to_pte_range() with that unaligned address causing soft lockup. Fix it by round up GUARD_SZ to PAGE_SIZE << 1 so that the division by 2 in bpf_arena_get_kern_vm_start() returns a page-aligned value.

Affected products

Linux kernel: from 6.9 before 6.12.17; from 6.13 before 6.13.5; 6.9, 6.14-rc1, 6.14-rc2, 6.14-rc3 — fixed in 6.12.17, 6.13.5

How to fix

Upgrade to a fixed version: Linux kernel 6.12.17, 6.13.5. Check the vendor advisory for mitigations.

References

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