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mm: avoid setting up anonymous pages into file mapping

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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>
(cherry picked from commit 6b7339f4c31ad69c8e9c0b2859276e22cf72176d)

Change-Id: I1bb2bd41b5c4686c50172aabe38bcd2adb3744f4
This commit is contained in:
Kirill A. Shutemov 2015-07-06 20:18:37 +00:00 committed by Sean McCreary
parent 3160f3db63
commit f0dbe032d9
1 changed files with 13 additions and 7 deletions
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20
mm/memory.c
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@ -3135,6 +3135,10 @@ 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_SIGBUS;
@ -3394,6 +3398,9 @@ static int do_linear_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;
return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
}
@ -3452,13 +3459,12 @@ int handle_pte_fault(struct mm_struct *mm,
entry = *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,
pte, pmd, flags, entry);
}
return do_anonymous_page(mm, vma, address,
pte, pmd, flags);
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);
}
if (pte_file(entry))
return do_nonlinear_fault(mm, vma, address,