[to-be-updated] x86-mm-pat-acquire-init_mm-read-lock-on-attribute-change-to-avoid-uaf.patch removed from -mm tree

The quilt patch titled
     Subject: x86/mm/pat: acquire init_mm read lock on attribute change to avoid UAF
has been removed from the -mm tree.  Its filename was
     x86-mm-pat-acquire-init_mm-read-lock-on-attribute-change-to-avoid-uaf.patch

This patch was dropped because an updated version will be issued

------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <[email protected]>
Subject: x86/mm/pat: acquire init_mm read lock on attribute change to avoid UAF
Date: Fri, 17 Jul 2026 18:30:09 +0100

A previous commit protected us against races between ptdump and CPA
collapse, however one still exists between attribute changes and collapse
as reported by Denis V.  Lunev (linked).

When an attribute change arises, a lockless page table walker obtains a
PTE entry, which is later written to via set_pte_atomic():

...
-> change_page_attr_set_clr()
-> __change_page_attr_set_clr()
-> __change_page_attr()
	-> _lookup_address_cpa()
	-> lookup_address_in_pgd_attr()
	-> [ lockless page table walker ]
-> set_pte_atomic()

There is nothing preventing a concurrent CPA collapse which can free the
PTE that was retrieved here, resulting in a use-after-free.

With the mmap write lock taken on init_mm over CPA collapse, we can now
resolve this race by acquiring an mmap read lock on init_mm over
__change_page_attr_set_clr().

This locks across the whole operation over which the walk and the PTE
entry write occurs, solving the race.

It is safe to do this here, as no spinlocks are held upon entry to
__change_page_attr_set_clr().

The CPA_COLLAPSE flag is only set by set_memory_rox(), which exclusively
operates upon vmalloc ranges, and on x86 only within the module mapping
space.

This is important, because some callers directly invoke
__change_page_attr_set_clr(), bypassing this lock.  However, none of these
operate within the module mapping space.

* cpa_process_alias() - a recursive helper called by
  __change_page_attr_set_clr().
* __set_memory_enc_pgtable() - operates on the direct mapping and (via
  __vmbus_establish_gpadl()) the vmalloc mapping space.
* __set_pages_[n]p() - called by set_direct_map_[invalid, default,
  valid]_noflush(), __kernel_map_pages() - operates on the direct map.
* kernel_[un]map_pages_in_pgd() - operates on EFI ranges.

This work is based upon Denis V.  Lunev's excellent analysis of the bug
with gratitude.

Link: https://lore.kernel.org/all/[email protected]/
Link: https://lore.kernel.org/[email protected]
Fixes: 41d88484c71c ("x86/mm/pat: restore large ROX pages after fragmentation")
Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: "Borislav Petkov (AMD)" <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Carlier <[email protected]>
Cc: David Hildenbrand (Arm) <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Kiryl Shutsemau <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport (Microsoft) <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Toshi Kani <[email protected]>
Cc: "Uladzislau Rezki (Sony)" <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 arch/x86/mm/pat/set_memory.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/mm/pat/set_memory.c~x86-mm-pat-acquire-init_mm-read-lock-on-attribute-change-to-avoid-uaf
+++ a/arch/x86/mm/pat/set_memory.c
@@ -2122,7 +2122,9 @@ static int change_page_attr_set_clr(unsi
 	cpa.curpage = 0;
 	cpa.force_split = force_split;
 
-	ret = __change_page_attr_set_clr(&cpa, 1);
+	/* Avoid race with concurrent CPA collapse. */
+	scoped_guard(mmap_read_lock, &init_mm)
+		ret = __change_page_attr_set_clr(&cpa, 1);
 
 	/*
 	 * Check whether we really changed something:
_

Patches currently in -mm which might be from [email protected] are

mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch
arm64-remove-redundant-concurrent-ptdump-uaf-mitigation.patch
x86-mm-pat-allocate-split-page-tables-as-kernel-page-tables.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
mm-mseal-remove-superfluous-comments-fix-confusion-around-mm.patch
mm-mseal-limit-scope-of-mseal-address-zero-to-address-zero.patch
mm-mseal-remove-further-superfluous-comments-do_mseal.patch
mm-vma-introduce-vma-virtual-page-offset-field-and-add-helpers.patch
mm-introduce-linear_virt_page_index.patch
mm-abstract-vma_address-and-introduce-vma_anon_address.patch
mm-update-print_bad_page_map-to-show-virtual-page-index.patch
mm-introduce-and-use-vma_filebacked_address.patch
mm-propagate-vma-virtual-page-offset-on-map-remap-split-merge.patch
mm-rmap-track-whether-the-page-vma-mapped-walk-is-anonymous.patch
mm-introduce-and-use-linear_folio_page_index.patch
mm-rmap-use-virt-pgoff-for-map_private-file-backed-anon-folios.patch
tools-testing-vma-expand-vma-merge-tests-to-assert-virt-pgoff.patch
tools-testing-selftests-mm-test-virtual-page-offset-merge-behaviour.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