linux-kernel - [RFC PATCH v2 2/2] mm/mremap: Expose abnormal new_pte during move

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Message-Id: <20250527132351.2050820-3-pulehui@huaweicloud.com>
Date: Tue, 27 May 2025 13:23:51 +0000
From: Pu Lehui <pulehui@...weicloud.com>
To: mhiramat@...nel.org,
	oleg@...hat.com,
	peterz@...radead.org,
	akpm@...ux-foundation.org,
	Liam.Howlett@...cle.com,
	lorenzo.stoakes@...cle.com,
	vbabka@...e.cz,
	jannh@...gle.com,
	pfalcato@...e.de
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	pulehui@...wei.com
Subject: [RFC PATCH v2 2/2] mm/mremap: Expose abnormal new_pte during move_ptes

From: Pu Lehui <pulehui@...wei.com>

When executing move_ptes, the new_pte must be NULL, otherwise it will be
overwritten by the old_pte, and cause the abnormal new_pte to be leaked.
In order to make this problem to be more explicit, let's add
WARN_ON_ONCE when new_pte is not NULL.

Suggested-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Pu Lehui <pulehui@...wei.com>
---
 mm/mremap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/mremap.c b/mm/mremap.c
index 83e359754961..adb3a111b5c1 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -237,6 +237,8 @@ static int move_ptes(struct pagetable_move_control *pmc,
 
 	for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 				   new_pte++, new_addr += PAGE_SIZE) {
+		WARN_ON_ONCE(!pte_none(*new_pte))
+
 		if (pte_none(ptep_get(old_pte)))
 			continue;
 
-- 
2.34.1