linux-kernel - [PATCH 4.17 01/56] userfaultfd: hugetlbfs: fix userfaultfd_huge_must

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Message-Id: <20180710182503.601211213@linuxfoundation.org>
Date:   Tue, 10 Jul 2018 20:24:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.17 01/56] userfaultfd: hugetlbfs: fix userfaultfd_huge_must_wait() pte access

4.17-stable review patch.  If anyone has any objections, please let me know.

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

From: Janosch Frank <frankja@...ux.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@...ux.ibm.com>
Reviewed-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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;