From: Muchun Song <songmuchun@xxxxxxxxxxxxx> Subject: 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/20220210123058.79206-7-songmuchun@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx> Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Fam Zheng <fam.zheng@xxxxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Lars Persson <lars.persson@xxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/userfaultfd.c | 3 +++ 1 file changed, 3 insertions(+) --- a/mm/userfaultfd.c~mm-userfaultfd-fix-missing-cache-flush-in-mcopy_atomic_pte-and-__mcopy_atomic +++ a/mm/userfaultfd.c @@ -150,6 +150,8 @@ static int mcopy_atomic_pte(struct mm_st /* 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); _
