[PATCH 3.18 43/68] mm: avoid setting up anonymous pages into file mapping

From: Greg Kroah-Hartman
Date: Fri May 05 2017 - 14:48:46 EST

3.18-stable review patch. If anyone has any objections, please let me know.


From: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

commit 6b7339f4c31ad69c8e9c0b2859276e22cf72176d upstream.

Reading page fault handler code I've noticed that under right
circumstances kernel would map anonymous pages into file mappings: if
the VMA doesn't have vm_ops->fault() and the VMA wasn't fully populated
on ->mmap(), kernel would handle page fault to not populated pte with

Let's change page fault handler to use do_anonymous_page() only on
anonymous VMA (->vm_ops == NULL) and make sure that the VMA is not

For file mappings without vm_ops->fault() or shred VMA without vm_ops,
page fault on pte_none() entry would lead to SIGBUS.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Willy Tarreau <w@xxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Amit Pundir <amit.pundir@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

mm/memory.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2629,6 +2629,10 @@ static int do_anonymous_page(struct mm_s


+ /* File mapping without ->vm_ops ? */
+ if (vma->vm_flags & VM_SHARED)
/* Check if we need to add a guard page to the stack */
if (check_stack_guard_page(vma, address) < 0)
@@ -3033,6 +3037,9 @@ static int do_linear_fault(struct mm_str
- vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

+ /* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND */
+ if (!vma->vm_ops->fault)
if (!(flags & FAULT_FLAG_WRITE))
return do_read_fault(mm, vma, address, pmd, pgoff, flags,
@@ -3198,11 +3205,9 @@ static int handle_pte_fault(struct mm_st
entry = ACCESS_ONCE(*pte);
if (!pte_present(entry)) {
if (pte_none(entry)) {
- if (vma->vm_ops) {
- if (likely(vma->vm_ops->fault))
- return do_linear_fault(mm, vma, address,
+ if (vma->vm_ops)
+ return do_linear_fault(mm, vma, address,
pte, pmd, flags, entry);
- }
return do_anonymous_page(mm, vma, address,
pte, pmd, flags);