linux-kernel - [PATCH v4 20/27] userfaultfd: wp: support write protection for userfault vma range

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Message-Id: <20190426045151.19556-21-peterx@redhat.com>
Date:   Fri, 26 Apr 2019 12:51:44 +0800
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Maya Gokhale <gokhale2@...l.gov>,
        Jerome Glisse <jglisse@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>, peterx@...hat.com,
        Martin Cracauer <cracauer@...s.org>, Shaohua Li <shli@...com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Marty McFadden <mcfadden8@...l.gov>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Rik van Riel <riel@...hat.com>
Subject: [PATCH v4 20/27] userfaultfd: wp: support write protection for userfault vma range

From: Shaohua Li <shli@...com>

Add API to enable/disable writeprotect a vma range. Unlike mprotect,
this doesn't split/merge vmas.

Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Kirill A. Shutemov <kirill@...temov.name>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Shaohua Li <shli@...com>
Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
[peterx:
 - use the helper to find VMA;
 - return -ENOENT if not found to match mcopy case;
 - use the new MM_CP_UFFD_WP* flags for change_protection
 - check against mmap_changing for failures]
Reviewed-by: Jerome Glisse <jglisse@...hat.com>
Reviewed-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 include/linux/userfaultfd_k.h |  3 ++
 mm/userfaultfd.c              | 54 +++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 765ce884cec0..8f6e6ed544fb 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -39,6 +39,9 @@ extern ssize_t mfill_zeropage(struct mm_struct *dst_mm,
 			      unsigned long dst_start,
 			      unsigned long len,
 			      bool *mmap_changing);
+extern int mwriteprotect_range(struct mm_struct *dst_mm,
+			       unsigned long start, unsigned long len,
+			       bool enable_wp, bool *mmap_changing);
 
 /* mm helpers */
 static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma,
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 2606409572b2..70cea2ff3960 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -639,3 +639,57 @@ ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
 {
 	return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing, 0);
 }
+
+int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
+			unsigned long len, bool enable_wp, bool *mmap_changing)
+{
+	struct vm_area_struct *dst_vma;
+	pgprot_t newprot;
+	int err;
+
+	/*
+	 * Sanitize the command parameters:
+	 */
+	BUG_ON(start & ~PAGE_MASK);
+	BUG_ON(len & ~PAGE_MASK);
+
+	/* Does the address range wrap, or is the span zero-sized? */
+	BUG_ON(start + len <= start);
+
+	down_read(&dst_mm->mmap_sem);
+
+	/*
+	 * If memory mappings are changing because of non-cooperative
+	 * operation (e.g. mremap) running in parallel, bail out and
+	 * request the user to retry later
+	 */
+	err = -EAGAIN;
+	if (mmap_changing && READ_ONCE(*mmap_changing))
+		goto out_unlock;
+
+	err = -ENOENT;
+	dst_vma = vma_find_uffd(dst_mm, start, len);
+	/*
+	 * Make sure the vma is not shared, that the dst range is
+	 * both valid and fully within a single existing vma.
+	 */
+	if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
+		goto out_unlock;
+	if (!userfaultfd_wp(dst_vma))
+		goto out_unlock;
+	if (!vma_is_anonymous(dst_vma))
+		goto out_unlock;
+
+	if (enable_wp)
+		newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
+	else
+		newprot = vm_get_page_prot(dst_vma->vm_flags);
+
+	change_protection(dst_vma, start, start + len, newprot,
+			  enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE);
+
+	err = 0;
+out_unlock:
+	up_read(&dst_mm->mmap_sem);
+	return err;
+}
-- 
2.17.1