> On Oct 27, 2021, at 12:52 PM, Yang Shi <shy828301@xxxxxxxxx> wrote: > > 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); Am I misreading this? If we return here for vma->vm_file, the following logic (shmem_file(), etc.) would be skipped, no? Thanks, Song > - } > + > + /* 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 >
