* + mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch added to mm-hotfixes-unstable branch
@ 2026-07-14 1:58 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-07-14 1:58 UTC (permalink / raw)
To: mm-commits, will, vbabka, urezki, toshi.kani, surenb, stable,
shakeel.butt, ryan.roberts, rppt, peterz, mingo, mhocko, luto,
liam, kas, hpa, dev.jain, david, catalin.marinas, bp, ljs, akpm
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
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*** 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 <ljs@kernel.org>
Subject: mm/ptdump: always stabilise against page table freeing using init_mm
Date: Sun, 12 Jul 2026 11:42:26 +0100
x86 and arm64 invoke ptdump_walk_pgd() with non-init_mm mm whilst still
walking kernel page table ranges.
For x86 this is done in ptdump_curknl_show() and ptdump_efi_show(), the
first passing current->mm, and the second passing efi_mm (we reach kernel
mappings that init_mm protects for current->mm due to x86 cloning shared
kernel page tables for arbitrary mm's).
arm64 does so via ptdump_debugfs_register(), configured by efi_ptdump_info
for efi ranges against efi_mm.
The init_mm mmap lock is used to stabilise page table freeing against
ptdump, so take a nested lock on init_mm to ensure that we are correctly
stabilised.
We take this after mmap write locking the non-init_mm mm. Nothing
acquires the init_mm lock first before locking an arbitrary mm, so no
deadlock is possible.
The preceding patches in this series updated the two cases which can cause
races with ptdump in init_mm ranges - vmap and x86 CPA huge page
promotion.
For arm64, commit fa93b45fd397 ("arm64: Enable vmalloc-huge with ptdump")
already provides exclusion against init_mm for the vmap case, which this
patch also pairs with.
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.
Also update walk_page_range_debug() to assert that init_mm is write
locked, add a comment explaining why and remove some redundant code.
We do not need to check for walk.mm being non-NULL, as the mmap lock
asserts would NULL pointer deref if it was (and of course no callers do
this).
The rest of this code is exactly as it would be if invoking
walk_kernel_page_table_range(), only now it's far clearer that that's the
case.
Link: https://lore.kernel.org/20260712-series-vmap-race-fix-v2-3-ad134cc3a12a@kernel.org
Fixes: b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page table")
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
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
^ permalink raw reply [flat|nested] 2+ messages in thread
* + mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch added to mm-hotfixes-unstable branch
@ 2026-07-14 19:12 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-07-14 19:12 UTC (permalink / raw)
To: mm-commits, ljs, akpm
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 <ljs@kernel.org>
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 <ljs@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
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
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-07-14 19:12 UTC | newest]
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2026-07-14 19:12 + mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch added to mm-hotfixes-unstable branch Andrew Morton
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2026-07-14 1:58 Andrew Morton
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