Skip to content
Permalink
Browse files Browse the repository at this point in the history
mm: avoid setting up anonymous pages into file mapping
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
do_anonymous_page().

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
shared.

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@linux.intel.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Willy Tarreau <w@1wt.eu>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  • Loading branch information
kiryl authored and torvalds committed Jul 9, 2015
1 parent 883a2df commit 6b7339f
Showing 1 changed file with 13 additions and 7 deletions.
20 changes: 13 additions & 7 deletions mm/memory.c
Expand Up @@ -2670,6 +2670,10 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,

pte_unmap(page_table);

/* File mapping without ->vm_ops ? */
if (vma->vm_flags & VM_SHARED)
return VM_FAULT_SIGBUS;

/* Check if we need to add a guard page to the stack */
if (check_stack_guard_page(vma, address) < 0)
return VM_FAULT_SIGSEGV;
Expand Down Expand Up @@ -3099,6 +3103,9 @@ static int do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
- vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

pte_unmap(page_table);
/* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND */
if (!vma->vm_ops->fault)
return VM_FAULT_SIGBUS;
if (!(flags & FAULT_FLAG_WRITE))
return do_read_fault(mm, vma, address, pmd, pgoff, flags,
orig_pte);
Expand Down Expand Up @@ -3244,13 +3251,12 @@ static int handle_pte_fault(struct mm_struct *mm,
barrier();
if (!pte_present(entry)) {
if (pte_none(entry)) {
if (vma->vm_ops) {
if (likely(vma->vm_ops->fault))
return do_fault(mm, vma, address, pte,
pmd, flags, entry);
}
return do_anonymous_page(mm, vma, address,
pte, pmd, flags);
if (vma->vm_ops)
return do_fault(mm, vma, address, pte, pmd,
flags, entry);

return do_anonymous_page(mm, vma, address, pte, pmd,
flags);
}
return do_swap_page(mm, vma, address,
pte, pmd, flags, entry);
Expand Down

0 comments on commit 6b7339f

Please sign in to comment.