linux-kernel - [PATCH 4/5] mm/mseal: separate out and simplify VMA gap check

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Message-ID: <f010ec1ce65f35dbe1fbd82ce002ea833a7128f3.1752497324.git.lorenzo.stoakes@oracle.com>
Date: Mon, 14 Jul 2025 14:00:39 +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>
Subject: [PATCH 4/5] mm/mseal: separate out and simplify VMA gap check

The check_mm_seal() function is doing something general - checking whether
a range contains only VMAs (or rather that it does NOT contain any unmapped
regions).

Generalise this and put the logic in mm/vma.c - introducing
range_contains_unmapped(). Additionally we can simplify the logic, we are
simply checking whether the last vma->vm_end has either a VMA starting
after it or ends before the end parameter.

No functional change intended.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 mm/mseal.c | 38 +++-----------------------------------
 mm/vma.c   | 18 ++++++++++++++++++
 mm/vma.h   |  3 +++
 3 files changed, 24 insertions(+), 35 deletions(-)

diff --git a/mm/mseal.c b/mm/mseal.c
index adbcc65e9660..8e4c605af700 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -37,34 +37,6 @@ static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	return ret;
 }

-/*
- * Check for do_mseal:
- * 1> start is part of a valid vma.
- * 2> end is part of a valid vma.
- * 3> No gap (unallocated address) between start and end.
- * 4> map is sealable.
- */
-static int check_mm_seal(unsigned long start, unsigned long end)
-{
-	struct vm_area_struct *vma;
-	unsigned long nstart = start;
-	VMA_ITERATOR(vmi, current->mm, start);
-
-	/* going through each vma to check. */
-	for_each_vma_range(vmi, vma, end) {
-		if (vma->vm_start > nstart)
-			/* unallocated memory found. */
-			return -ENOMEM;
-
-		if (vma->vm_end >= end)
-			return 0;
-
-		nstart = vma->vm_end;
-	}
-
-	return -ENOMEM;
-}
-
 /*
  * Apply sealing.
  */
@@ -184,14 +156,10 @@ int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
 	if (mmap_write_lock_killable(mm))
 		return -EINTR;

-	/*
-	 * First pass, this helps to avoid
-	 * partial sealing in case of error in input address range,
-	 * e.g. ENOMEM error.
-	 */
-	ret = check_mm_seal(start, end);
-	if (ret)
+	if (range_contains_unmapped(mm, start, end)) {
+		ret = -ENOMEM;
 		goto out;
+	}

 	/*
 	 * Second pass, this should success, unless there are errors
diff --git a/mm/vma.c b/mm/vma.c
index b3d880652359..b57545568ae6 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -3203,3 +3203,21 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)

 	return 0;
 }
+
+/* Does the [start, end) range contain any unmapped memory? */
+bool range_contains_unmapped(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
+{
+	struct vm_area_struct *vma;
+	unsigned long prev_end = start;
+	VMA_ITERATOR(vmi, current->mm, start);
+
+	for_each_vma_range(vmi, vma, end) {
+		if (vma->vm_start > prev_end)
+			return true;
+
+		prev_end = vma->vm_end;
+	}
+
+	return prev_end < end;
+}
diff --git a/mm/vma.h b/mm/vma.h
index d17f560cf53d..bfe9a04e6018 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -598,4 +598,7 @@ int create_init_stack_vma(struct mm_struct *mm, struct vm_area_struct **vmap,
 int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift);
 #endif

+bool range_contains_unmapped(struct mm_struct *mm,
+		unsigned long start, unsigned long end);
+
 #endif	/* __MM_VMA_H */
--
2.50.1