linux-kernel - [PATCH v3 2/7] mm/munmap: Replace can_modify_mm with can_modify

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Message-Id: <20240817-mseal-depessimize-v3-2-d8d2e037df30@gmail.com>
Date: Sat, 17 Aug 2024 01:18:29 +0100
From: Pedro Falcato <pedro.falcato@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Vlastimil Babka <vbabka@...e.cz>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Shuah Khan <shuah@...nel.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, jeffxu@...omium.org, oliver.sang@...el.com, 
 torvalds@...ux-foundation.org, Michael Ellerman <mpe@...erman.id.au>, 
 Kees Cook <kees@...nel.org>, Pedro Falcato <pedro.falcato@...il.com>
Subject: [PATCH v3 2/7] mm/munmap: Replace can_modify_mm with
 can_modify_vma

We were doing an extra mmap tree traversal just to check if the entire
range is modifiable. This can be done when we iterate through the VMAs
instead.

Signed-off-by: Pedro Falcato <pedro.falcato@...il.com>
---
 mm/mmap.c | 11 +----------
 mm/vma.c  | 19 ++++++++++++-------
 2 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 3af256bacef3..30ae4cb5cec9 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1740,16 +1740,7 @@ int do_vma_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		unsigned long start, unsigned long end, struct list_head *uf,
 		bool unlock)
 {
-	struct mm_struct *mm = vma->vm_mm;
-
-	/*
-	 * Check if memory is sealed, prevent unmapping a sealed VMA.
-	 * can_modify_mm assumes we have acquired the lock on MM.
-	 */
-	if (unlikely(!can_modify_mm(mm, start, end)))
-		return -EPERM;
-
-	return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
+	return do_vmi_align_munmap(vmi, vma, vma->vm_mm, start, end, uf, unlock);
 }
 
 /*
diff --git a/mm/vma.c b/mm/vma.c
index 84965f2cd580..5850f7c0949b 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -712,6 +712,12 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
 			goto map_count_exceeded;
 
+		/* Don't bother splitting the VMA if we can't unmap it anyway */
+		if (!can_modify_vma(vma)) {
+			error = -EPERM;
+			goto start_split_failed;
+		}
+
 		error = __split_vma(vmi, vma, start, 1);
 		if (error)
 			goto start_split_failed;
@@ -723,6 +729,11 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	 */
 	next = vma;
 	do {
+		if (!can_modify_vma(next)) {
+			error = -EPERM;
+			goto modify_vma_failed;
+		}
+
 		/* Does it split the end? */
 		if (next->vm_end > end) {
 			error = __split_vma(vmi, next, end, 0);
@@ -815,6 +826,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	__mt_destroy(&mt_detach);
 	return 0;
 
+modify_vma_failed:
 clear_tree_failed:
 userfaultfd_error:
 munmap_gather_failed:
@@ -860,13 +872,6 @@ int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
 	if (end == start)
 		return -EINVAL;
 
-	/*
-	 * Check if memory is sealed, prevent unmapping a sealed VMA.
-	 * can_modify_mm assumes we have acquired the lock on MM.
-	 */
-	if (unlikely(!can_modify_mm(mm, start, end)))
-		return -EPERM;
-
 	/* Find the first overlapping VMA */
 	vma = vma_find(vmi, end);
 	if (!vma) {

-- 
2.46.0