userfaultfd: hugetlbfs: fix userfaultfd_huge_must_wait() pte access

BugLink: http://bugs.launchpad.net/bugs/1808399
commit 1e2c043628c7736dd56536d16c0ce009bc834ae7 upstream.

Use huge_ptep_get() to translate huge ptes to normal ptes so we can
check them with the huge_pte_* functions.  Otherwise some architectures
will check the wrong values and will not wait for userspace to bring in
the memory.

Link: http://lkml.kernel.org/r/20180626132421.78084-1-frankja@linux.ibm.com
Fixes: 369cd2121be4 ("userfaultfd: hugetlbfs: userfaultfd_huge_must_wait for hugepmd ranges")
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 41a75f9f23fdbfc2d30ae80b979a331484f0dcf9..a0e445fc02b39611935c03558d0606ce3214ad9a 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -220,24 +220,26 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
                                         unsigned long reason)
 {
        struct mm_struct *mm = ctx->mm;
-       pte_t *pte;
+       pte_t *ptep, pte;
        bool ret = true;
 
        VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
 
-       pte = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
-       if (!pte)
+       ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
+
+       if (!ptep)
                goto out;
 
        ret = false;
+       pte = huge_ptep_get(ptep);
 
        /*
         * Lockless access: we're in a wait_event so it's ok if it
         * changes under us.
         */
-       if (huge_pte_none(*pte))
+       if (huge_pte_none(pte))
                ret = true;
-       if (!huge_pte_write(*pte) && (reason & VM_UFFD_WP))
+       if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
                ret = true;
 out:
        return ret;