linux-kernel - Re: [PATCH v4 4/5] mm/mseal: simplify and rename VMA gap check

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Message-ID: <d85b3d55-09dc-43ba-8204-b48267a96751@lucifer.local>
Date: Fri, 25 Jul 2025 19:41:16 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        David Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Jeff Xu <jeffxu@...omium.org>, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v4 4/5] mm/mseal: simplify and rename VMA gap check

Hi Andrew,

Can you apply the attached trivial fix-patch which adds a clarifying comment to
mm/mseal.c.

Thanks, Lorenzo


----8<----
>From bf8211317183353b3652baac1af1d35555733d2b Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Date: Fri, 25 Jul 2025 19:23:50 +0100
Subject: [PATCH] mm/mseal: add comment explaining why we disallow gaps on
 mseal()

This explains the semantics clearly, the 'why' of the situation.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 mm/mseal.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/mseal.c b/mm/mseal.c
index 1059322add34..d140f569c4c3 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -37,6 +37,18 @@ static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	return ret;
 }

+/*
+ * mseal() disallows an input range which contain unmapped ranges (VMA holes).
+ *
+ * It disallows unmapped regions from start to end whether they exist at the
+ * start, in the middle, or at the end of the range, or any combination thereof.
+ *
+ * This is because after sealng a range, there's nothing to stop memory mapping
+ * of ranges in the remaining gaps later, meaning that the user might then
+ * wrongly consider the entirety of the mseal()'d range to be sealed when it
+ * in fact isn't.
+ */
+
 /*
  * Does the [start, end) range contain any unmapped memory?
  *
--
2.50.1