From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BF58C316199 for ; Tue, 15 Sep 2026 01:09:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789434547; cv=none; b=lxjvp7nkpQkC8T4JOhB7UCMqA18z5/fgC4Vnh5QmXcll5oJyxMiGAmlhRWw33hS9NegUDEpwOeRzo5LsshPEjpxb5trI5oPiQsm41dCQ7DQI77CS4Fa7JW4OwM7y8B4VyMhcwQOSJZwr5mkomtOCMzCtOnyPX8VOcg88CiAvgxw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789434547; c=relaxed/simple; bh=BvfIT0pLCXyQgVvXL9nihOpR1vB2DbHI85izUKUeKZ8=; h=Date:To:From:Subject:Message-Id; b=EaqgVLuCjY8z9T4MONf53WiDvhtVAqb1FsHdcLkQ0Wc4niQ8UMZvwKGQMHKa4DMjx9Gk8A1m/7TQYTRig6iE/W1Ba/KIs0bIl1o4PscmSRmmHXYPGAlm20NyeePbdY1b3gqfHgbJ3ecK5y50XspFeA94cDSQvP+OwOrUInEgNK0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=W+qYcS1f; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="W+qYcS1f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E2581F000FF; Tue, 15 Sep 2026 01:09:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789434545; bh=0kwRHqU1fFa7D0INlN5X/KNRAKUN4dP8g23/w4TzigI=; h=Date:To:From:Subject; b=W+qYcS1fK9w8XSJtIt2mwyGuNtb0lLXyXSb6mS9URrzKR96EEQDKdSG3z0WxVYLaa Uxnk67wZcymgCJ6DcmCaZOUX4hrLox0W23gR94tvSjvFvFsz93BOKJC2Of9DLJU6OI w6YOsVhgPmezbQEEY9UTdaBDbWSjuiWbnO/JMzkM= Date: Mon, 14 Sep 2026 18:09:04 -0700 To: mm-commits@vger.kernel.org,ljs@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-kernel-owned.patch added to mm-new branch Message-Id: <20260915010905.3E2581F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/vma: only allow mmap to clear VMA_MAYWRITE_BIT if kernel-owned has been added to the -mm mm-new branch. Its filename is mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-kernel-owned.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-kernel-owned.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: "Lorenzo Stoakes (ARM)" Subject: mm/vma: only allow mmap to clear VMA_MAYWRITE_BIT if kernel-owned Date: Mon, 14 Sep 2026 15:57:36 +0100 For ordinary files the only way the VMA_MAYWRITE_BIT flag is cleared is if the underlying file is itself read-only. This means that mprotect() cannot mark a shared mapping of a read-only file as read/write, as doing so would violate the read only attribute, and permit writes. In general, we do not want file systems to be able to do this for read/write files. Doing so would violate fundamental user expectation of file attributes and likely break userspace. However, drivers pose a tricky problem here - the /dev/xxx file may be read/write but provide access to a resource which is fundamentally read-only. Therefore we must allow drivers to be able to clear VMA_MAYWRITE_BIT. To achieve both of these things, restrict this ability to kernel-owned mappings as identified by vma_flags_is_kernel_owned(). This constrains this ability to drivers which own the mapping's contents, whether memory-mapped I/O, kernel-allocated pages, or ordinary pages they map themselves, and so define its semantics. Every in-tree mmap hook which clears VMA_MAYWRITE_BIT, some twenty sites across drivers, filesystems and bpf, establishes a kernel-owned mapping, with usbmon and the ALSA PCM status page converted earlier in this series to do so. Note that drivers may, if they do not gate on VMA_SHARED_BIT, be able to disable MAP_PRIVATE-file-backed mapping CoW semantics. This is perhaps not always intended, but we retain this capacity to maintain existing behaviour. As all drivers which clear VMA_MAYWRITE_BIT establish kernel-owned mappings, no functional change is intended. Link: https://lore.kernel.org/20260914-b4-mmap-prepare-vma-flag-sanify-v2-16-7d9781ed5361@kernel.org Signed-off-by: Lorenzo Stoakes (ARM) Signed-off-by: Andrew Morton --- mm/vma.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/mm/vma.c~mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-kernel-owned +++ a/mm/vma.c @@ -2795,6 +2795,11 @@ static int mmap_validate(unsigned long p if (WARN_ON_ONCE(!was_maywrite && is_maywrite)) return -EINVAL; + /* Only kernel-owned mappings may clear VMA_MAYWRITE_BIT. */ + if (!vma_flags_is_kernel_owned(curr_flags) && + WARN_ON_ONCE(was_maywrite && !is_maywrite)) + return -EINVAL; + return mmap_validate_vma_flags(curr_flags); } _ Patches currently in -mm which might be from ljs@kernel.org are mm-vmpressure-remove-window-size-todo.patch tools-testing-selftests-mm-add-missing-gitignore-entries.patch mm-move-drivers-char-memc-to-mm-char-memc.patch mm-implement-file_is_dev_zero-to-uniquely-identify-dev-zero.patch mm-vma-only-permit-map_private-dev-zero-to-be-mapped-anonymous.patch mm-vma-make-map_private-mapped-dev-zero-mappings-truly-anonymous.patch tools-testing-vma-add-test-to-assert-map_private-dev-zero-is-anon.patch tools-testing-selftests-mm-add-map_private-dev-zero-merge-tests.patch mm-madvise-swap-in-cowd-map_private-file-mappings-on-madv_willneed.patch mm-huge_memory-zap-deposited-page-tables-after-an-rcu-grace-period.patch mm-enable-mmu_gather_rcu_table_free-for-most-2-level-architectures.patch mm-enable-mmu_gather_rcu_table_free-for-mmu-riscv.patch mm-enable-mmu_gather_rcu_table_free-for-mmu-arm.patch mm-enable-mmu_gather_rcu_table_free-for-arc-microblaze-xtensa.patch mm-enable-mmu_gather_rcu_table_free-for-sparc64.patch mm-enable-mmu_gather_rcu_table_free-for-m68k-coldfire.patch mm-enable-mmu_gather_rcu_table_free-for-sh-x2.patch mm-enable-mmu_gather_rcu_table_free-for-m68k-motorola.patch mm-enable-mmu_gather_rcu_table_free-for-sparc32.patch mm-make-userland-page-table-freeing-rcu-safe.patch mm-change-the-contract-for-free_pgtables-update-docs.patch mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get.patch mm-vma-predicate-setting-mmap_prepare-vma-fields-on-new-vma-alloc.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-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_kernel_owned-predicates.patch mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-kernel-owned.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-only-kernel-owned-mappings-may-set-vma_io_bit.patch mm-remove-vma_io_bit-check-in-vma_is_kernel_owned.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-madvise-update-is_valid_guard_vma-to-use-vma_can_merge.patch mm-vma-introduce-vma_is_persistent.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-introduce-and-use-vma_can_gup.patch