The patch titled Subject: mm: khugepaged: skip huge page collapse for special files has been added to the -mm tree. Its filename is mm-khugepaged-skip-huge-page-collapse-for-special-files.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-khugepaged-skip-huge-page-colla... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-khugepaged-skip-huge-page-colla...

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------------------------------------------------------ From: Yang Shi shy828301@gmail.com Subject: mm: khugepaged: skip huge page collapse for special files

The read-only THP for filesystems will collapse THP for files opened readonly and mapped with VM_EXEC. The intended usecase is to avoid TLB misses for large text segments. But it doesn't restrict the file types so a THP could be collapsed for a non-regular file, for example, block device, if it is opened readonly and mapped with EXEC permission. This may cause bugs, like [1] and [2].

This is definitely not the intended usecase, so just collapse THP for regular files in order to close the attack surface.

[1] https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+... [2] https://lore.kernel.org/linux-mm/000000000000c6a82505ce284e4c@google.com/

Link: https://lkml.kernel.org/r/20211027195221.3825-1-shy828301@gmail.com Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Signed-off-by: Hugh Dickins hughd@google.com Signed-off-by: Yang Shi shy828301@gmail.com Reported-by: Hao Sun sunhao.th@gmail.com Reported-by: syzbot+aae069be1de40fb11825@syzkaller.appspotmail.com Cc: Matthew Wilcox willy@infradead.org Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Song Liu songliubraving@fb.com Cc: Andrea Righi andrea.righi@canonical.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/khugepaged.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)

--- a/mm/khugepaged.c~mm-khugepaged-skip-huge-page-collapse-for-special-files +++ a/mm/khugepaged.c @@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm if (!transhuge_vma_enabled(vma, vm_flags)) return false;

- /* Enabled via shmem mount options or sysfs settings. */ - if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) { + if (vma->vm_file) return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, HPAGE_PMD_NR); - } + + /* Enabled via shmem mount options or sysfs settings. */ + if (shmem_file(vma->vm_file)) + return shmem_huge_enabled(vma);

/* THP settings require madvise. */ if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) return false;

- /* Read-only file mappings need to be aligned for THP to work. */ + /* Only regular file is valid */ if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file && - !inode_is_open_for_write(vma->vm_file->f_inode) && (vm_flags & VM_EXEC)) { - return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, - HPAGE_PMD_NR); + struct inode *inode = vma->vm_file->f_inode; + + return !inode_is_open_for_write(inode) && + S_ISREG(inode->i_mode); }

if (!vma->anon_vma || vma->vm_ops) _

Patches currently in -mm which might be from shy828301@gmail.com are

mm-hwpoison-remove-the-unnecessary-thp-check.patch mm-filemap-check-if-thp-has-hwpoisoned-subpage-for-pmd-page-fault.patch mm-khugepaged-skip-huge-page-collapse-for-special-files.patch mm-khugepaged-skip-huge-page-collapse-for-special-files-fix.patch mm-filemap-coding-style-cleanup-for-filemap_map_pmd.patch mm-hwpoison-refactor-refcount-check-handling.patch mm-shmem-dont-truncate-page-if-memory-failure-happens.patch mm-hwpoison-handle-non-anonymous-thp-correctly.patch mm-migrate-make-demotion-knob-depend-on-migration.patch