[PATCH 5.15 17/21] mm: shmem: fix missing cache flush in shmem_mfill_atomic_pte()

Greg Kroah-Hartman
2022-05-13T14:34:51Z

From: Muchun Song <songmuchun@bytedance.com>

commit 19b482c29b6f3805f1d8e93015847b89e2f7f3b1 upstream.

userfaultfd calls shmem_mfill_atomic_pte() which does 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. Insert flush_dcache_page() in non-zero-page case. And replace
clear_highpage() with clear_user_highpage() which already considers the
cache maintenance.

Link: https://lkml.kernel.org/r/20220210123058.79206-6-songmuchun@bytedance.com
Fixes: 8d1039634206 ("userfaultfd: shmem: add shmem_mfill_zeropage_pte for userfaultfd support")
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lars Persson <lars.persson@axis.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Cc: Zi Yan <ziy@nvidia.com>
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>
---
mm/shmem.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2394,8 +2394,10 @@ int shmem_mfill_atomic_pte(struct mm_str
/* don't free the page */
goto out_unacct_blocks;
}
+
+ flush_dcache_page(page);
} else { /* ZEROPAGE */
- clear_highpage(page);
+ clear_user_highpage(page, dst_addr);
}
} else {
page = *pagep;