CVE-2025-38447: 
Linux Ubuntu vulnerability analysis and mitigation

CVE-2025-38447 is a vulnerability discovered in the Linux kernel related to potential out-of-bounds page table access during batched unmap operations. The vulnerability was disclosed on July 25, 2025, affecting the memory management (mm/rmap) subsystem of the Linux kernel (NVD).

The vulnerability exists in the try_to_unmap_one() function where the batched unmap logic may read past the end of a PTE table when a large folio's PTE mappings are not fully contained within a single page table. While this scenario is considered rare, the vulnerability is exploitable from userspace. The issue was resolved by refactoring the logic into a new helper function called folio_unmap_pte_batch(), which correctly calculates the safe batch size by capping the scan at both the VMA and PMD boundaries (NVD).

The vulnerability could lead to out-of-bounds memory access, potentially causing system instability or information disclosure. Since the issue is triggerable from userspace, it poses a security risk regardless of its likelihood of occurrence (NVD).

The vulnerability has been patched by implementing a new helper function folio_unmap_pte_batch() that properly handles the batch size calculations and boundary checks. The fix includes support for partial batching, allowing any number of pages from 1 up to the calculated safe maximum (NVD).