mm: userfaultfd: fix missing cache flush in mcopy_atomic_pte() and __mcopy_atomic()

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.

Link: https://lkml.kernel.org/r/[email protected]
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 <[email protected]>
Cc: Axel Rasmussen <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Fam Zheng <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Lars Persson <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Xiongchun Duan <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 3 insertions, 0 deletions

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 @@ retry:
 				err = -EFAULT;
 				goto out;
 			}
+			flush_dcache_page(page);
 			goto retry;
 		} else
 			BUG_ON(page);