linux-kernel - [PATCH] userfaultfd: hugetlbfs: Fix userfaultfd_huge_must

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Date:   Tue, 26 Jun 2018 14:24:21 +0100
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     mike.kravetz@...cle.com, aarcange@...hat.com
Cc:     linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Subject: [PATCH] userfaultfd: hugetlbfs: Fix userfaultfd_huge_must_wait pte access

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.

Signed-off-by: Janosch Frank <frankja@...ux.ibm.com>
Fixes: 369cd2121be4 ("userfaultfd: hugetlbfs: userfaultfd_huge_must_wait for hugepmd ranges")
---
 fs/userfaultfd.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 123bf7d516fc..594d192b2331 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -222,24 +222,26 @@ 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;
-- 
2.14.3