linux-kernel - [PATCH v3 5/5] mm/mseal: rework mseal apply logic

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Message-ID: <9ae70e1c509d790cf174f16e491975efd9be50b6.1752687069.git.lorenzo.stoakes@oracle.com>
Date: Wed, 16 Jul 2025 18:38:06 +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 v3 5/5] mm/mseal: rework mseal apply logic

The logic can be simplified - firstly by renaming the inconsistently named
apply_mm_seal() to mseal_apply().

We then wrap mseal_fixup() into the main loop as the logic is simple enough
to not require it, equally it isn't a hugely pleasant pattern in mprotect()
etc.  so it's not something we want to perpetuate.

We eliminate the need for invoking vma_iter_end() on each loop by directly
determining if the VMA was merged - the only thing we need concern
ourselves with is whether the start/end of the (gapless) range are offset
into VMAs.

This refactoring also avoids the rather horrid 'pass pointer to prev
around' pattern used in mprotect() et al.

No functional change intended.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Reviewed-by: Pedro Falcato <pfalcato@...e.de>
Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>
Acked-by: David Hildenbrand <david@...hat.com>
---
 mm/mseal.c | 67 ++++++++++++++++--------------------------------------
 1 file changed, 20 insertions(+), 47 deletions(-)

diff --git a/mm/mseal.c b/mm/mseal.c
index 61c07b1369cb..0ab12e09792a 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -15,28 +15,6 @@
 #include <linux/sched.h>
 #include "internal.h"
 
-static int mseal_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
-		struct vm_area_struct **prev, unsigned long start,
-		unsigned long end, vm_flags_t newflags)
-{
-	int ret = 0;
-	vm_flags_t oldflags = vma->vm_flags;
-
-	if (newflags == oldflags)
-		goto out;
-
-	vma = vma_modify_flags(vmi, *prev, vma, start, end, newflags);
-	if (IS_ERR(vma)) {
-		ret = PTR_ERR(vma);
-		goto out;
-	}
-
-	vm_flags_set(vma, VM_SEALED);
-out:
-	*prev = vma;
-	return ret;
-}
-
 /* Does the [start, end) range contain any unmapped memory? */
 static bool range_contains_unmapped(struct mm_struct *mm,
 		unsigned long start, unsigned long end)
@@ -55,38 +33,33 @@ static bool range_contains_unmapped(struct mm_struct *mm,
 	return prev_end < end;
 }
 
-/*
- * Apply sealing.
- */
-static int apply_mm_seal(unsigned long start, unsigned long end)
+static int mseal_apply(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
 {
-	unsigned long nstart;
 	struct vm_area_struct *vma, *prev;
-	VMA_ITERATOR(vmi, current->mm, start);
+	unsigned long curr_start = start;
+	VMA_ITERATOR(vmi, mm, start);
 
+	/* We know there are no gaps so this will be non-NULL. */
 	vma = vma_iter_load(&vmi);
-	/*
-	 * Note: check_mm_seal should already checked ENOMEM case.
-	 * so vma should not be null, same for the other ENOMEM cases.
-	 */
 	prev = vma_prev(&vmi);
 	if (start > vma->vm_start)
 		prev = vma;
 
-	nstart = start;
 	for_each_vma_range(vmi, vma, end) {
-		int error;
-		unsigned long tmp;
-		vm_flags_t newflags;
-
-		newflags = vma->vm_flags | VM_SEALED;
-		tmp = vma->vm_end;
-		if (tmp > end)
-			tmp = end;
-		error = mseal_fixup(&vmi, vma, &prev, nstart, tmp, newflags);
-		if (error)
-			return error;
-		nstart = vma_iter_end(&vmi);
+		unsigned long curr_end = MIN(vma->vm_end, end);
+
+		if (!(vma->vm_flags & VM_SEALED)) {
+			vma = vma_modify_flags(&vmi, prev, vma,
+					curr_start, curr_end,
+					vma->vm_flags | VM_SEALED);
+			if (IS_ERR(vma))
+				return PTR_ERR(vma);
+			vm_flags_set(vma, VM_SEALED);
+		}
+
+		prev = vma;
+		curr_start = curr_end;
 	}
 
 	return 0;
@@ -185,10 +158,10 @@ int do_mseal(unsigned long start, size_t len_in, unsigned long flags)
 	 * reaching the max supported VMAs, however, those cases shall
 	 * be rare.
 	 */
-	ret = apply_mm_seal(start, end);
+	ret = mseal_apply(mm, start, end);
 
 out:
-	mmap_write_unlock(current->mm);
+	mmap_write_unlock(mm);
 	return ret;
 }
 
-- 
2.50.1