linux-kernel - [PATCH 4.9 7/7] mm: userfaultfd: fix missing cache flush in mcopy_atomic_pte() and __mcopy

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Message-Id: <20220513142226.131430745@linuxfoundation.org>
Date:   Fri, 13 May 2022 16:23:22 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Muchun Song <songmuchun@...edance.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Fam Zheng <fam.zheng@...edance.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lars Persson <lars.persson@...s.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Peter Xu <peterx@...hat.com>,
        Xiongchun Duan <duanxiongchun@...edance.com>,
        Zi Yan <ziy@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 7/7] mm: userfaultfd: fix missing cache flush in mcopy_atomic_pte() and __mcopy_atomic()

From: Muchun Song <songmuchun@...edance.com>

commit 7c25a0b89a487878b0691e6524fb5a8827322194 upstream.

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@bytedance.com
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@...edance.com>
Cc: Axel Rasmussen <axelrasmussen@...gle.com>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Fam Zheng <fam.zheng@...edance.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Lars Persson <lars.persson@...s.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Peter Xu <peterx@...hat.com>
Cc: Xiongchun Duan <duanxiongchun@...edance.com>
Cc: Zi Yan <ziy@...dia.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/userfaultfd.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -50,6 +50,8 @@ static int mcopy_atomic_pte(struct mm_st
 			/* don't free the page */
 			goto out;
 		}
+
+		flush_dcache_page(page);
 	} else {
 		page = *pagep;
 		*pagep = NULL;
@@ -267,6 +269,7 @@ retry:
 				err = -EFAULT;
 				goto out;
 			}
+			flush_dcache_page(page);
 			goto retry;
 		} else
 			BUG_ON(page);