+ mm-khugepaged-skip-huge-page-collapse-for-special-files.patch added to -mm tree

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-collapse-for-special-files.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-khugepaged-skip-huge-page-collapse-for-special-files.patch

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------------------------------------------------------
From: Yang Shi <redacted>
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+f5vA@mail.gmail.com/ (local)
[2] https://lore.kernel.org/linux-mm/000000000000c6a82505ce284e4c@google.com/ (local)

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 <redacted>
Reported-by: Hao Sun <redacted>
Reported-by: syzbot+aae069be1de40fb11825@syzkaller.appspotmail.com
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Kirill A. Shutemov <redacted>
Cc: Song Liu <redacted>
Cc: Andrea Righi <redacted>
Cc: <redacted>
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-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