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Subject[PATCH 4.14 01/53] userfaultfd: hugetlbfs: fix userfaultfd_huge_must_wait() pte access
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Janosch Frank <frankja@linux.ibm.com>

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>

---
fs/userfaultfd.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -220,24 +220,26 @@ static inline bool userfaultfd_huge_must
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;

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