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From:   Muchun Song <songmuchun@bytedance.com>
To:     akpm@linux-foundation.org, zi.yan@cs.rutgers.edu,
        kirill.shutemov@linux.intel.com, rientjes@google.com,
        lars.persson@axis.com, mike.kravetz@oracle.com, ziy@nvidia.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        duanxiongchun@bytedance.com, fam.zheng@bytedance.com,
        Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH v5 6/7] mm: userfaultfd: fix missing cache flush in mcopy_atomic_pte() and __mcopy_atomic()
Date:   Thu, 10 Feb 2022 20:30:57 +0800
Message-Id: <20220210123058.79206-7-songmuchun@bytedance.com>
In-Reply-To: <20220210123058.79206-1-songmuchun@bytedance.com>
References: <20220210123058.79206-1-songmuchun@bytedance.com>
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The userfaultfd calls mcopy_atomic_pte() and __mcopy_atomic() which do not
do any cache flushing for the target page.  Then the target page will be
mapped to the user space with a different address (user address), which might
have an alias issue with the kernel address used to copy the data from the
user to.  Fix this by insert flush_dcache_page() after copy_from_user()
succeeds.

Fixes: b6ebaedb4cb1 ("userfaultfd: avoid mmap_sem read recursion in mcopy_atomic")
Fixes: c1a4de99fada ("userfaultfd: mcopy_atomic|mfill_zeropage: UFFDIO_COPY|UFFDIO_ZEROPAGE preparation")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/userfaultfd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 0780c2a57ff1..6ccc534d1c1c 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -150,6 +150,8 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 			/* don't free the page */
 			goto out;
 		}
+
+		flush_dcache_page(page);
 	} else {
 		page = *pagep;
 		*pagep = NULL;
@@ -625,6 +627,7 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
 				err = -EFAULT;
 				goto out;
 			}
+			flush_dcache_page(page);
 			goto retry;
 		} else
 			BUG_ON(page);
-- 
2.11.0