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().
There's chance that it was done intentionally, but I don't see good
justification for this. We just hide bugs in broken drivers.
Let's change page fault handler to use do_anonymous_page() only on
anonymous VMA (->vm_ops == NULL).
For file mappings without vm_ops->fault() page fault on pte_none() entry
would lead to SIGBUS.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
mm/memory.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 8a2fc9945b46..f3ee782059e3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3115,6 +3115,9 @@ 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);
+
+ if (unlikely(!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);
@@ -3260,13 +3263,13 @@ 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);
+ if (!vma->vm_ops) {
+ return do_anonymous_page(mm, vma, address, pte,
+ pmd, flags);
+ } else {
+ 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);
--
2.1.4
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