mm: avoid setting up anonymous pages into file mapping (6b7339f4) · Commits · 戴 / test

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>

mm/memory.c

+13 −7

Original line number	Diff line number	Diff line
		@@ -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;
		@@ -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);
		@@ -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);

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