linux-kernel - [PATCH v4 09/14] mm/mprotect: Break COW PTE before changing protection

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Message-Id: <20230207035139.272707-10-shiyn.lin@gmail.com>
Date:   Tue,  7 Feb 2023 11:51:34 +0800
From:   Chih-En Lin <shiyn.lin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
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        Michal Hocko <mhocko@...e.com>,
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        Alexey Gladkov <legion@...nel.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
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        Dinglan Peng <peng301@...due.edu>,
        Pedro Fonseca <pfonseca@...due.edu>,
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        Chih-En Lin <shiyn.lin@...il.com>
Subject: [PATCH v4 09/14] mm/mprotect: Break COW PTE before changing protection

If the PTE table is COW-ed, break it before changing the protection.

Signed-off-by: Chih-En Lin <shiyn.lin@...il.com>
---
 mm/mprotect.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 61cf60015a8b..8b18cd0e5c5e 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -103,6 +103,9 @@ static unsigned long change_pte_range(struct mmu_gather *tlb,
 	if (pmd_trans_unstable(pmd))
 		return 0;
 
+	if (break_cow_pte(vma, pmd, addr))
+		return 0;
+
 	/*
 	 * The pmd points to a regular pte so the pmd can't change
 	 * from under us even if the mmap_lock is only hold for
@@ -314,6 +317,12 @@ static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
 		return 1;
 	if (pmd_trans_huge(pmdval))
 		return 0;
+	/*
+	 * If the entry point to COW-ed PTE, it's write protection bit
+	 * will cause pmd_bad().
+	 */
+	if (!pmd_write(pmdval))
+		return 0;
 	if (unlikely(pmd_bad(pmdval))) {
 		pmd_clear_bad(pmd);
 		return 1;
-- 
2.34.1