Linux Kernel Page Table Management Vulnerability in Arm64 Architecture

A vulnerability in the Linux kernel's memory management for the arm64 architecture has been addressed. The issue arose from an incorrect handling of the file_map_count for non-leaf page middle directory (pmd) and page upper directory (pud) entries. This mismanagement triggered an unexpected kernel BUG when collapsing huge pages, leading to a crash. The root cause was that the pmd_user_accessible_page function did not verify if a pmd was a leaf, causing it to improperly decrease the file_map_count for non-leaf pmds. The vulnerability has been fixed by ensuring that the pmd and pud user accessibility checks only apply to leaf entries.

Impact

The vulnerability could cause a kernel crash due to an unhandled BUG condition, disrupting system operations and potentially leading to a denial of service.