6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zhiling Zou [ Upstream commit 8db4bab826ccc9ec10fa41736a48031cd338d392 ] page_table_check_set() and page_table_check_clear() account mappings based on PageAnon(). Shared zero-page PTEs and huge zero PMDs are special mappings, but page_table_check can still account them as file-backed pages. An unprivileged process can populate enough zero mappings to overflow file_map_count and hit the existing BUG_ON(). The PTE path can do this with the shared zero page, and the PMD path can do the same with huge zero mappings. Skip special zero mappings in the user page-table accounting paths. Keep the PTE-side pte_special() check, and identify huge zero PMDs from the mapped folio instead of pmd_special(). That covers architectures where pmd_special() is a no-op without adding huge_zero_pfn checks to the generic counter helpers. Link: https://lore.kernel.org/cover.1784717203.git.zhilinz@nebusec.ai Link: https://lore.kernel.org/e94478e4fb7912fb7e8ebebed5ce85d00dc9a69d.1784717203.git.zhilinz@nebusec.ai Fixes: df4e817b7108 ("mm: page table check") Signed-off-by: Zhiling Zou Signed-off-by: Ren Wei Reported-by: Vega Cc: Pasha Tatashin Assisted-by: Codex:gpt-5.4 Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- mm/page_table_check.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/mm/page_table_check.c b/mm/page_table_check.c index ee52927e9e66b..2efa910eef23e 100644 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -165,18 +165,29 @@ void __page_table_check_pte_clear(struct mm_struct *mm, pte_t pte) if (&init_mm == mm) return; - if (pte_user_accessible_page(pte)) { + if (pte_user_accessible_page(pte) && !pte_special(pte)) { page_table_check_clear(pte_pfn(pte), PAGE_SIZE >> PAGE_SHIFT); } } EXPORT_SYMBOL(__page_table_check_pte_clear); +static inline bool page_table_check_huge_zero_pmd(pmd_t pmd) +{ + unsigned long pfn = pmd_pfn(pmd); + + if (!pfn_valid(pfn)) + return false; + + return is_huge_zero_folio(page_folio(pfn_to_page(pfn))); +} + void __page_table_check_pmd_clear(struct mm_struct *mm, pmd_t pmd) { if (&init_mm == mm) return; - if (pmd_user_accessible_page(pmd)) { + if (pmd_user_accessible_page(pmd) && + !page_table_check_huge_zero_pmd(pmd)) { page_table_check_clear(pmd_pfn(pmd), PMD_SIZE >> PAGE_SHIFT); } } @@ -221,7 +232,7 @@ void __page_table_check_ptes_set(struct mm_struct *mm, pte_t *ptep, pte_t pte, for (i = 0; i < nr; i++) __page_table_check_pte_clear(mm, ptep_get(ptep + i)); - if (pte_user_accessible_page(pte)) + if (pte_user_accessible_page(pte) && !pte_special(pte)) page_table_check_set(pte_pfn(pte), nr, pte_write(pte)); } EXPORT_SYMBOL(__page_table_check_ptes_set); @@ -246,7 +257,8 @@ void __page_table_check_pmd_set(struct mm_struct *mm, pmd_t *pmdp, pmd_t pmd) page_table_check_pmd_flags(pmd); __page_table_check_pmd_clear(mm, *pmdp); - if (pmd_user_accessible_page(pmd)) { + if (pmd_user_accessible_page(pmd) && + !page_table_check_huge_zero_pmd(pmd)) { page_table_check_set(pmd_pfn(pmd), PMD_SIZE >> PAGE_SHIFT, pmd_write(pmd)); } -- 2.53.0