From 248925a1e722495038002cad286022b89c215368 Mon Sep 17 00:00:00 2001 From: Wang Kui Date: Mon, 27 Oct 2025 11:56:49 +0800 Subject: [PATCH] mm/hugetlb: fix folio is still mapped when deleted mainline inclusion from mainline-v6.17 commit 7b7387650dcf2881fd8bb55bcf3c8bd6c9542dd7 bugzilla: https://gitee.com/src-openeuler/kernel/issues/ID2QM9 CVE: CVE-2025-40006 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7b7387650dcf2881fd8bb55bcf3c8bd6c9542dd7 ------------------- Migration may be raced with fallocating hole. remove_inode_single_folio will unmap the folio if the folio is still mapped. However, it's called without folio lock. If the folio is migrated and the mapped pte has been converted to migration entry, folio_mapped() returns false, and won't unmap it. Due to extra refcount held by remove_inode_single_folio, migration fails, restores migration entry to normal pte, and the folio is mapped again. As a result, we triggered BUG in filemap_unaccount_folio. The log is as follows: BUG: Bad page cache in process hugetlb pfn:156c00 page: refcount:515 mapcount:0 mapping:0000000099fef6e1 index:0x0 pfn:0x156c00 head: order:9 mapcount:1 entire_mapcount:1 nr_pages_mapped:0 pincount:0 aops:hugetlbfs_aops ino:dcc dentry name(?):"my_hugepage_file" flags: 0x17ffffc00000c1(locked|waiters|head|node=0|zone=2|lastcpupid=0x1fffff) page_type: f4(hugetlb) page dumped because: still mapped when deleted CPU: 1 UID: 0 PID: 395 Comm: hugetlb Not tainted 6.17.0-rc5-00044-g7aac71907bde-dirty #484 NONE Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015 Call Trace: dump_stack_lvl+0x4f/0x70 filemap_unaccount_folio+0xc4/0x1c0 __filemap_remove_folio+0x38/0x1c0 filemap_remove_folio+0x41/0xd0 remove_inode_hugepages+0x142/0x250 hugetlbfs_fallocate+0x471/0x5a0 vfs_fallocate+0x149/0x380 Hold folio lock before checking if the folio is mapped to avold race with migration. Link: https://lkml.kernel.org/r/20250912074139.3575005-1-tujinjiang@huawei.com Fixes: 4aae8d1c051e ("mm/hugetlbfs: unmap pages if page fault raced with hole punch") Signed-off-by: Jinjiang Tu Cc: David Hildenbrand Cc: Kefeng Wang Cc: Matthew Wilcox (Oracle) Cc: Muchun Song Cc: Oscar Salvador Cc: Signed-off-by: Andrew Morton Signed-off-by: sy --- include/linux/mm_types.h | 5 +++++ mm/hugetlb.c | 15 +++++---------- 2 files changed, 10 insertions(+), 10 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 64c38b09e18d..451248286590 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -534,6 +534,11 @@ static inline int ptdesc_pmd_pts_count(struct ptdesc *ptdesc) { return atomic_read(&ptdesc->pt_share_count); } + +static inline bool ptdesc_pmd_is_shared(struct ptdesc *ptdesc) +{ + return !!ptdesc_pmd_pts_count(ptdesc); +} #else static inline void ptdesc_pmd_pts_init(struct ptdesc *ptdesc) { diff --git a/mm/hugetlb.c b/mm/hugetlb.c index bad0dcf0faeb..0ce0958e4b34 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5362,18 +5362,13 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, break; } - /* - * If the pagetables are shared don't copy or take references. - * - * dst_pte == src_pte is the common case of src/dest sharing. - * However, src could have 'unshared' and dst shares with - * another vma. So page_count of ptep page is checked instead - * to reliably determine whether pte is shared. - */ - if (page_count(virt_to_page(dst_pte)) > 1) { +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING + /* If the pagetables are shared, there is nothing to do */ + if (ptdesc_pmd_is_shared(virt_to_ptdesc(dst_pte))) { addr |= last_addr_mask; continue; } +#endif dst_ptl = huge_pte_lock(h, dst, dst_pte); src_ptl = huge_pte_lockptr(h, src, src_pte); @@ -7358,7 +7353,7 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, hugetlb_vma_assert_locked(vma); if (sz != PMD_SIZE) return 0; - if (!ptdesc_pmd_pts_count(virt_to_ptdesc(ptep))) + if (!ptdesc_pmd_is_shared(virt_to_ptdesc(ptep))) return 0; pud_clear(pud); -- Gitee