+ mm-vma-ensure-mmap_prepare-doesnt-set-actions-on-a-mergeable-vma.patch added to mm-unstable branch

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

The patch titled
     Subject: mm/vma: ensure mmap_prepare doesn't set actions on a mergeable vma
has been added to the -mm mm-unstable branch.  Its filename is
     mm-vma-ensure-mmap_prepare-doesnt-set-actions-on-a-mergeable-vma.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vma-ensure-mmap_prepare-doesnt-set-actions-on-a-mergeable-vma.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/vma: ensure mmap_prepare doesn't set actions on a mergeable vma
Date: Tue, 13 Oct 2026 16:04:44 +0100

When a user requests an mmap_action be performed in mmap_prepare, this
involves populating the VMA range with data.

However, if the VMA is mergeable, it might then mistakenly be merged with
another VMA without having populated the range.

Every mmap action currently available sets VMA flags such that the VMA
cannot be merged.

However, to ensure that no future mmap action falls foul of this, assert
that this is the case upon mmap_prepare validation.

Link: https://lore.kernel.org/20261013-b4-mmap-prepare-vma-flag-sanify-v6-4-1aa3c9b139f9@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
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---

 mm/vma.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/mm/vma.c~mm-vma-ensure-mmap_prepare-doesnt-set-actions-on-a-mergeable-vma
+++ a/mm/vma.c
@@ -2830,6 +2830,18 @@ static int mmap_validate(unsigned long o
 int mmap_prepare_validate(const struct vm_area_desc *orig_desc,
 			  const struct vm_area_desc *desc)
 {
+	/*
+	 * It is not valid to execute mmap actions for VMAs which can be merged,
+	 * as any such merge would leave portions of the mapping incorrectly
+	 * unmapped.
+	 *
+	 * This is checked after mmap_action_prepare(), as it may update the VMA
+	 * flags and therefore whether the VMA can be merged.
+	 */
+	if (vma_flags_can_merge(&desc->vma_flags) &&
+	    WARN_ON_ONCE(desc->action.type != MMAP_NOTHING))
+		return -EINVAL;
+
 	return mmap_validate(orig_desc->start, orig_desc->end,
 			     desc->start, desc->end,
 			     &orig_desc->vma_flags, &desc->vma_flags);
_

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

mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get.patch
mm-vma-introduce-and-use-vma_can_merge.patch
mm-consistently-validate-vma-state-after-mmap-hooks.patch
mm-vma-ensure-mmap_prepare-doesnt-set-actions-on-a-mergeable-vma.patch
mm-make-map_kernel_pages_-internal-and-unexported.patch
mm-vma-tidy-up-map-kernel-pages-enum-values.patch
mm-assert-mmap-lock-held-use-new-flags-api-in-vm_insert_page.patch
mm-add-mmap-action-for-discontiguous-kernel-page-mapping.patch
docs-filesystems-update-mmap_prepare-docs-for-discontig-kernel-pgs.patch
drivers-usb-mon-update-to-use-mmap_prepare-map-kernel-pages.patch
infiniband-update-hfi1-to-use-remap_vmalloc_range.patch
selinux-reject-writable-opens-of-policy-file-drop-mmap-shared-write-check.patch
alsa-pcm-use-vm_insert_page-to-map-pcm-status-page.patch
bpf-arena-mark-arena_map_mmap-mappings-vm_mixedmap.patch
mm-vma-add-vma_is_mm_managed-predicates.patch
mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-not-mm-managed.patch
mm-vma-add-and-use-vma__is_fixed_mapping.patch
scsi-sg-convert-mmap-hook-to-mmap_prepare-and-rework.patch
fbdev-defio-assert-fbinfo_virtfb-drop-vm_io-add-vm_mixedmap.patch
hsi-cmt_speech-convert-mmap-hook-to-mmap_prepare-refactor.patch
mm-gup-error-out-early-on-vma_mayread_bit-vmas.patch
uprobes-remove-vm_io-set-vm_mixedmap-for-mapped-kernel-pages.patch
mm-mlock-clear-vma_locked_mask-over-mmap-callback.patch
mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify.patch
mm-vma-enforce-that-mm-managed-mappings-may-not-set-vma_io_bit.patch
mm-remove-vma_io_bit-check-in-vma_is_mm_managed.patch
mm-remove-hugetlb_inlineh.patch
mm-rename-is_vm_hugetlb_page-to-vma_is_hugetlb.patch
mm-drop-some-redundant-checks-around-hugetlb-vmas.patch
mm-vma-introduce-vma_is_mm_backed.patch
mm-madvise-update-is_valid_guard_vma-to-use-vma_is_mm_backed.patch
mm-uffd-use-predicates-for-userfaultfd-checks.patch
mm-madvise-use-predicates-for-madvise-madv_dofork.patch
mm-eliminate-vma_special_flags-usage-when-hugetlb-explicitly-tested.patch
mm-eliminate-vma_special_flags-check-in-lru_gen_look_around.patch
mm-avoid-use-of-vma_special_flags-in-migrate_vma_setup.patch
mm-eliminate-vm_special-vma_special_flags.patch
fuse-dax-do-not-set-vm_mixedmap.patch
mm-huge_memory-remove-vma_is_special_huge.patch
mm-vma-const-ify-vma_assert_stabilised-and-associated-functions.patch
mm-implement-and-use-vma_has_anon_rmap-silence-kcsan.patch
mm-update-comments-to-refer-to-anon-rmap-rather-than-anon_vma.patch
mm-vma-dont-remove-vma-from-rmap-if-pgoff-unchanged.patch