In the Linux kernel, the following vulnerability has been resolved: powerpc/64s: Fix unmap race with PMD migration entries The following race is possible with migration swap entries or device-private THP entries. e.g. when move_pages is called on a PMD THP page, then there maybe an intermediate state, where PMD entry acts as a migration swap entry (pmd_present() is true). Then if an munmap happens at the same time, then this VM_BUG_ON() can happen in pmdp_huge_get_and_clear_full(). This patch fixes that. Thread A: move_pages() syscall add_folio_for_migration() mmap_read_lock(mm) folio_isolate_lru(folio) mmap_read_unlock(mm) do_move_pages_to_node() migrate_pages() try_to_migrate_one() spin_lock(ptl) set_pmd_migration_entry() pmdp_invalidate() # PMD: _PAGE_INVALID | _PAGE_PTE | pfn set_pmd_at() # PMD: migration swap entry (pmd_present=0) spin_unlock(ptl) [page copy phase] # <--- RACE WIN
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