linux-kernel - [PATCH] mm/page_table_check: fix accessing unmapped ptep

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Date:   Thu, 26 May 2022 19:33:50 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>, <pasha.tatashin@...een.com>
CC:     <rientjes@...gle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <linmiaohe@...wei.com>
Subject: [PATCH] mm/page_table_check: fix accessing unmapped ptep

ptep is unmapped too early, so ptep will be accessed while it's unmapped.
Fix it by deferring pte_unmap() until page table checking is done.

Fixes: 80110bbfbba6 ("mm/page_table_check: check entries at pmd levels")
Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/page_table_check.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index 3692bea2ea2c..971c3129b0e3 100644
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -234,11 +234,11 @@ void __page_table_check_pte_clear_range(struct mm_struct *mm,
 		pte_t *ptep = pte_offset_map(&pmd, addr);
 		unsigned long i;
 
-		pte_unmap(ptep);
 		for (i = 0; i < PTRS_PER_PTE; i++) {
 			__page_table_check_pte_clear(mm, addr, *ptep);
 			addr += PAGE_SIZE;
 			ptep++;
 		}
+		pte_unmap(ptep);
 	}
 }
-- 
2.23.0