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+... [1] Link: https://lore.kernel.org/linux-mm/000000000000c6a82505ce284e4c@google.com/ [2] Link: https://lkml.kernel.org/r/CAHbLzkqTW9U3VvTu1Ki5v_cLRC9gHW+znBukg_ycergE0JWj-... [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 --- mm/khugepaged.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c index ee8812578563..5c36848022de 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -443,21 +443,24 @@ static bool hugepage_vma_check(struct vm_area_struct *vma, 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 && (vm_flags & VM_DENYWRITE)) { - return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, - HPAGE_PMD_NR); + struct inode *inode = vma->vm_file->f_inode; + + return S_ISREG(inode->i_mode); }

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