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 F1634418A23 for ; Tue, 14 Jul 2026 19:12:16 +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=1784056338; cv=none; b=Z1IC18zuaOLamdUDqJPvzl66/eZCQbr+H0bVYg1X3JlAIi6QiJ7ofblqQrnXe5q6zley6UrMWS/MNtNozxMrbWFUgp+v2c8SuxU8L3WY4m0R5k0YSvlGtb/hLYKyE2QrQwxPFqa1JyWxnJQHvmUT9YihjJtqIA8NXjalxlrzkXk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784056338; c=relaxed/simple; bh=z8EqkUX1+7KfXsThJlpAo4Ywg16EDCrtC36hkUogyt0=; h=Date:To:From:Subject:Message-Id; b=vFunQt/1gSB+0Qg1sWFqu+f83Jzf6PmEQWr+KGqKoVGrB1Ue/Gqk2zJrEzz79hosw/+xpPcLwMO7eVf6QPDISHP+lsS0ybCuCHoMmv3R9lnmBw+2XXVB3Txb+Jd2eSsUrAHW2lDDo+o5+6gwGJFRDpjSGvhZ4V2jacQ5ejp7Z44= 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=goAMBgkM; 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="goAMBgkM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 851701F000E9; Tue, 14 Jul 2026 19:12:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1784056336; bh=9sWJf6DnTdQw/dvTxD8LLMQqD0AFUk8/QQaGQk3U2b4=; h=Date:To:From:Subject; b=goAMBgkM2Ii2RBvRp32OoyvosPx81mW2cIvn7cV1cKywXK65kFw93KfJgOacmay5T f/QlgDYbwCUNl1qXOXirNo791IJ2LDJWLd2+BqjCZ3fZSP/lFxx2BW3dTkYkAV7VN4 a1bEFjFoNOYPdsnBi1UPssjmbUGjKb691qBK64Hk= Date: Tue, 14 Jul 2026 12:12:16 -0700 To: mm-commits@vger.kernel.org,ljs@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch added to mm-hotfixes-unstable branch Message-Id: <20260714191216.851701F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/ptdump: always stabilise against page table freeing using init_mm has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm 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 Subject: mm/ptdump: always stabilise against page table freeing using init_mm Date: Tue, 14 Jul 2026 18:24:25 +0100 Previous commits have established the invariant that kernel page table freeing is performed while an mmap read lock on init_mm is held, which fixes races between ptdump and kernel page table freeing over init_mm. However, x86 and arm64 can perform a ptdump over an mm other than init_mm via ptdump_walk_pgd() and since kernel memory ranges are shared across non-kernel mm's, this means that the race still exists for these cases. Fix this by acquiring a nested mmap write lock for init_mm in ptdump_walk_pgd(). This is safe as we take this after mmap write locking the mm, and nothing acquires the init_mm lock first before locking an arbitrary mm, so no deadlock is possible. Also update walk_page_range_debug() to assert that init_mm is write locked, add a comment explaining why and remove some redundant code, and eliminate the unnecessary and confusing invocation of walk_kernel_page_table_range(). We can safely remove the non-NULL check for walk.mm, as the mmap lock asserts would NULL pointer deref if it was (and of course no callers do this). The first point at which ptdump can race kernel page table freeing is commit b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page table"), so we target this in the Fixes tag. Link: https://lore.kernel.org/20260714-series-vmap-race-fix-v3-3-b812eccfa0f9@kernel.org Fixes: b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page table") Signed-off-by: Lorenzo Stoakes Reviewed-by: Mike Rapoport (Microsoft) Cc: Andy Lutomirski Cc: "Borislav Petkov (AMD)" Cc: Catalin Marinas Cc: David Hildenbrand Cc: Dev Jain Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Kiryl Shutsemau Cc: Liam R. Howlett Cc: Michal Hocko Cc: Peter Zijlstra Cc: Ryan Roberts Cc: Shakeel Butt Cc: Suren Baghdasaryan Cc: Toshi Kani Cc: "Uladzislau Rezki (Sony)" Cc: Vlastimil Babka Cc: Will Deacon Cc: Dave Hansen Cc: Signed-off-by: Andrew Morton --- mm/pagewalk.c | 14 +++++++++----- mm/ptdump.c | 7 +++++++ 2 files changed, 16 insertions(+), 5 deletions(-) --- a/mm/pagewalk.c~mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm +++ a/mm/pagewalk.c @@ -702,12 +702,16 @@ int walk_page_range_debug(struct mm_stru * to account for page table freeing on vmap huge page mapping. */ mmap_assert_write_locked(mm); + /* + * x86, arm64 ptdump allow walks of efi mm's and x86 ptdump allows walks + * of arbitrary mm's. + * + * However, they both must also hold the init_mm lock to account for + * concurrent kernel page table freeing. + */ + mmap_assert_write_locked(&init_mm); - /* For convenience, we allow traversal of kernel mappings. */ - if (mm == &init_mm) - return walk_kernel_page_table_range(start, end, ops, - pgd, private); - if (start >= end || !walk.mm) + if (start >= end) return -EINVAL; if (!check_ops_safe(ops)) return -EINVAL; --- a/mm/ptdump.c~mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm +++ a/mm/ptdump.c @@ -178,11 +178,18 @@ void ptdump_walk_pgd(struct ptdump_state get_online_mems(); mmap_write_lock(mm); + /* To stabilise kernel page tables we must hold the init_mm lock too. */ + if (mm != &init_mm) + mmap_write_lock_nested(&init_mm, SINGLE_DEPTH_NESTING); + while (range->start != range->end) { walk_page_range_debug(mm, range->start, range->end, &ptdump_ops, pgd, st); range++; } + + if (mm != &init_mm) + mmap_write_unlock(&init_mm); mmap_write_unlock(mm); put_online_mems(); _ Patches currently in -mm which might be from ljs@kernel.org are mm-vmalloc-acquire-init_mm-lock-on-huge-vmap-to-avoid-ptdump-uaf.patch x86-mm-pat-acquire-mmap-lock-on-page-table-free-to-avoid-ptdump-uaf.patch mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch arm64-remove-redundant-concurrent-ptdump-uaf-mitigation.patch mm-move-alloc-tag-to-mm.patch mm-move-vma_start_pgoff-into-mmh-and-clean-up.patch mm-add-kdoc-comments-for-vma_start-last_pgoff.patch tools-testing-vma-use-vma_start_pgoff-in-merge-tests.patch mm-introduce-and-use-vma_end_pgoff.patch mm-rmap-update-mm-interval_treec-comments.patch mm-rmap-parameterise-vma_interval_tree_-by-address_space.patch mm-rmap-elide-unnecessary-static-inlines-in-interval_treec.patch mm-rmap-rename-vma_interval_tree_-to-mapping_rmap_tree_.patch mm-rmap-parameterise-anon_vma_interval_tree_-by-anon_vma.patch mm-rmap-rename-anon_vma_interval_tree_-params-and-use-pgoff_t.patch mm-rmap-rename-anon_vma_interval_tree_-to-anon_rmap_tree_.patch maintainers-move-mm-interval_treec-to-rmap-section.patch mm-vma-introduce-and-use-vmg_pages-vmg__pgoff.patch mm-vma-clean-up-anon_vma_compatible.patch mm-vma-refactor-vmg_adjust_set_range-for-clarity.patch mm-vma-minor-cleanup-of-expand_.patch mm-introduce-and-use-linear_page_delta.patch mm-vma-use-vma_start_pgoff-linear_page_index-in-mm-code.patch mm-prefer-vma__pgoff-to-vma-vm_pgoff-in-kernel.patch mm-vma-remove-duplicative-vma_pgoff_offset-helper.patch mm-use-linear_page_-consistently.patch mm-vma-introduce-vma_assert_can_modify.patch mm-vma-add-and-use-vma__pgoff.patch mm-vma-move-__install_special_mapping-to-vmac.patch mm-vma-make-vma_set_range-static-drop-insert_vm_struct-decl.patch mm-vma-update-vma_shrink-to-not-pass-start-pgoff-parameters.patch mm-vma-update-vmg_adjust_set_range-to-offset-pgoff-instead.patch mm-vma-slightly-rework-the-anonymous-check-in-__mmap_new_vma.patch mm-vma-introduce-and-use-vma_set_pgoff.patch mm-vma-correct-incorrect-vmah-inclusion.patch mm-vma-use-guard-clauses-in-can_vma_merge_.patch tools-testing-vma-default-vma-mm-flag-bits-to-64-bit.patch tools-testing-vma-output-compared-expression-on-assert_.patch mm-introduce-vma_flags_can_grow-and-vma_can_grow.patch mm-vma-update-do_mmap-to-use-vma_flags_t.patch mm-convert-__get_unmapped_area-to-use-vma_flags_t.patch mm-update-generic_get_unmapped_area-to-use-vma_flags_t.patch mm-prefer-mm-def_vma_flags-in-mm-logic.patch mm-vma-convert-vm_pgprot_modify-to-use-vma_flags_t-and-rename.patch mm-vma-rename-vma_get_page_prot-to-vma_flags_to_page_prot.patch mm-introduce-vma_get_page_prot-and-use-it.patch mm-vma-update-create_init_stack_vma-to-use-vma_flags_t.patch mm-vma-convert-miscellaneous-uses-of-vma-flags-in-core-mm.patch mm-mlock-convert-mlock-code-to-use-vma_flags_t.patch mm-mprotect-convert-mprotect-code-to-use-vma_flags_t.patch mm-mremap-convert-mremap-code-to-use-vma_flags_t.patch