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    Subject[PATCH 5.14 036/125] mm: khugepaged: skip huge page collapse for special files
    Date
    From: Yang Shi <shy828301@gmail.com>

    commit a4aeaa06d45e90f9b279f0b09de84bd00006e733 upstream.

    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.

    [shy828301@gmail.com: fix vm_file check [3]]

    Link: https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+f5vA@mail.gmail.com/ [1]
    Link: https://lore.kernel.org/linux-mm/000000000000c6a82505ce284e4c@google.com/ [2]
    Link: https://lkml.kernel.org/r/CAHbLzkqTW9U3VvTu1Ki5v_cLRC9gHW+znBukg_ycergE0JWj-A@mail.gmail.com [3]
    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>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    mm/khugepaged.c | 19 +++++++++++--------
    1 file changed, 11 insertions(+), 8 deletions(-)

    --- a/mm/khugepaged.c
    +++ b/mm/khugepaged.c
    @@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm
    if (!transhuge_vma_enabled(vma, vm_flags))
    return false;

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

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