The read-only THP for filesystems would collapse THP for file opened readonly and mapped with VM_EXEC, the intended usecase is to avoid TLB miss for large text segment. But it doesn't restrict the file types so THP could be collapsed for 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 intended usecase, so just collapsing THP for regular file in order to close the attack surface. [1] https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+f5vA@xxxxxxxxxxxxxx/ [2] https://lore.kernel.org/linux-mm/000000000000c6a82505ce284e4c@xxxxxxxxxx/ Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Reported-by: Hao Sun <sunhao.th@xxxxxxxxx> Reported-by: syzbot+aae069be1de40fb11825@xxxxxxxxxxxxxxxxxxxxxxxxx Cc: Hao Sun <sunhao.th@xxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Song Liu <songliubraving@xxxxxx> Cc: Andrea Righi <andrea.righi@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> --- The patch is basically based off the proposal from Hugh (https://lore.kernel.org/linux-mm/a07564a3-b2fc-9ffe-3ace-3f276075ea5c@xxxxxxxxxx/). It seems Hugh is too busy to prepare the patch for formal submission (I didn't hear from him by pinging him a couple of times on mailing list), so I prepared the patch and added his SOB. mm/khugepaged.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 045cc579f724..e91b7271275e 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm_area_struct *vma, 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) -- 2.26.2
