[merged mm-hotfixes-stable] mm-vma-read-anon_vma-carefully-in-validate_mm.patch removed from -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The quilt patch titled
     Subject: mm/vma: read anon_vma carefully in validate_mm()
has been removed from the -mm tree.  Its filename was
     mm-vma-read-anon_vma-carefully-in-validate_mm.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/vma: read anon_vma carefully in validate_mm()
Date: Mon, 02 Nov 2026 10:25:20 +0000

Commit 38564710f443 ("mm: implement and use vma_has_anon_rmap(), silence
KCSAN") rather clumsily converted the read of vma->anon_vma into a
vma_has_anon_rmap() without accounting for the separation between
assignment of anon_vma and later use of it.

vma_has_anon_rmap() is intended as an optimistic check, so doesn't need to
protect against a torn read in vma->anon_vma. The caller is expected to
take care of this themselves if they then in fact access the field.

validate_mm() does indeed then reference the field, so resolve the issue
via READ_ONCE(), and simplify the code by separating this into a new
function validate_mm_anon_rmap().

Finally, add a vma_assert_stabilised() to make it clear the required state
of the VMA.

[kas@kernel.org: reduce ifdeffery]
  Link: https://lore.kernel.org/auhn01dpDzK47igy@thinkstation
Link: https://lore.kernel.org/20261102-fix-validate_mm-v1-1-5c309614ef15@kernel.org
Fixes: 38564710f443 ("mm: implement and use vma_has_anon_rmap(), silence KCSAN")
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: <syzbot+10e72ea5747737bcd2ad@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/6ae78418.6552420f.2a0efc.005c.GAE@google.com/
Reported-by: Songsen Yang <yangsongsen@insta360.com>
Closes: https://lore.kernel.org/all/20261102074414.10902-1-yangsongsen@insta360.com/
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
---

 include/linux/mm.h |    2 --
 mm/vma.c           |   34 ++++++++++++++++++++++------------
 2 files changed, 22 insertions(+), 14 deletions(-)

--- a/include/linux/mm.h~mm-vma-read-anon_vma-carefully-in-validate_mm
+++ a/include/linux/mm.h
@@ -4370,9 +4370,7 @@ anon_rmap_tree_iter_first(struct anon_vm
 struct anon_vma_chain *
 anon_rmap_tree_iter_next(struct anon_vma_chain *avc,
 			 pgoff_t pgoff_start, pgoff_t pgoff_last);
-#ifdef CONFIG_DEBUG_VM_RB
 void anon_rmap_tree_verify(struct anon_vma_chain *avc);
-#endif
 
 #define anon_rmap_tree_foreach(avc, anon_vma, pgoff_start, pgoff_last)		 \
 	for (avc = anon_rmap_tree_iter_first(anon_vma, pgoff_start, pgoff_last); \
--- a/mm/vma.c~mm-vma-read-anon_vma-carefully-in-validate_mm
+++ a/mm/vma.c
@@ -676,6 +676,26 @@ static int dup_anon_vma(struct vm_area_s
 }
 
 #ifdef CONFIG_DEBUG_VM_MAPLE_TREE
+static void validate_mm_anon_rmap(struct vm_area_struct *vma)
+{
+	struct anon_vma *anon_vma;
+	struct anon_vma_chain *avc;
+
+	if (!IS_ENABLED(CONFIG_DEBUG_VM_RB))
+		return;
+
+	vma_assert_stabilised(vma);
+
+	anon_vma = READ_ONCE(vma->anon_vma);
+	if (!anon_vma)
+		return;
+
+	anon_vma_lock_read(anon_vma);
+	list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
+		anon_rmap_tree_verify(avc);
+	anon_vma_unlock_read(anon_vma);
+}
+
 void validate_mm(struct mm_struct *mm)
 {
 	int bug = 0;
@@ -685,10 +705,6 @@ void validate_mm(struct mm_struct *mm)
 
 	mt_validate(&mm->mm_mt);
 	for_each_vma(vmi, vma) {
-#ifdef CONFIG_DEBUG_VM_RB
-		struct anon_vma *anon_vma = vma->anon_vma;
-		struct anon_vma_chain *avc;
-#endif
 		unsigned long vmi_start, vmi_end;
 		bool warn = 0;
 
@@ -709,14 +725,8 @@ void validate_mm(struct mm_struct *mm)
 			vma_iter_dump_tree(&vmi);
 		}
 
-#ifdef CONFIG_DEBUG_VM_RB
-		if (vma_has_anon_rmap(vma)) {
-			anon_vma_lock_read(anon_vma);
-			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
-				anon_rmap_tree_verify(avc);
-			anon_vma_unlock_read(anon_vma);
-		}
-#endif
+		validate_mm_anon_rmap(vma);
+
 		/* Check for a infinite loop */
 		if (++i > mm->map_count + 10) {
 			i = -1;
_

Patches currently in -mm which might be from ljs@kernel.org are