The patch titled
Subject: mm: ptep_clear() page table helper
has been added to the -mm tree. Its filename is
mm-ptep_clear-page-table-helper.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-ptep_clear-page-table-helper.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-ptep_clear-page-table-helper.patch
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------------------------------------------------------
From: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Subject: mm: ptep_clear() page table helper
Patch series "page table check".
Ensure that some memory corruptions are prevented by checking at the time
of insertion of entries into user page tables that there is no illegal
sharing.
We have recently found a problem [1] that existed in kernel since 4.14.
The problem was caused by broken page ref count and led to memory leaking
from one process into another. The problem was accidentally detected by
studying a dump of one process and noticing that one page contains memory
that should not belong to this process.
There are some other page->_refcount related problems that were recently
fixed: [2], [3] which potentially could also lead to illegal sharing.
In addition to hardening refcount [4] itself, this work is an attempt to
prevent this class of memory corruption issues.
It uses a simple state machine that is independent from regular MM logic
to check for illegal sharing at time pages are inserted and removed from
page tables.
[1] https://lore.kernel.org/all/xr9335nxwc5y.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
[2] https://lore.kernel.org/all/1582661774-30925-2-git-send-email-akaher@xxxxxxxxxx
[3] https://lore.kernel.org/all/20210622021423.154662-3-mike.kravetz@xxxxxxxxxx
[4] https://lore.kernel.org/all/20211026173822.502506-1-pasha.tatashin@xxxxxxxxxx
This patch (of 3):
We have ptep_get_and_clear() and ptep_get_and_clear_full() helpers to
clear PTE from user page tables, but there is no variant for simple clear
of a present PTE from user page tables without using a low level
pte_clear() which can be either native or para-virtualised.
Add a new ptep_clear() that can be used in common code to clear PTEs from
page table. We will need this call later in order to add a hook for page
table check.
Link: https://lkml.kernel.org/r/20211123214814.3756047-1-pasha.tatashin@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20211123214814.3756047-2-pasha.tatashin@xxxxxxxxxx
Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Wei Xu <weixugc@xxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/vm/arch_pgtable_helpers.rst | 6 ++++--
include/linux/pgtable.h | 8 ++++++++
mm/debug_vm_pgtable.c | 2 +-
mm/khugepaged.c | 12 ++----------
4 files changed, 15 insertions(+), 13 deletions(-)
--- a/Documentation/vm/arch_pgtable_helpers.rst~mm-ptep_clear-page-table-helper
+++ a/Documentation/vm/arch_pgtable_helpers.rst
@@ -66,9 +66,11 @@ PTE Page Table Helpers
+---------------------------+--------------------------------------------------+
| pte_mknotpresent | Invalidates a mapped PTE |
+---------------------------+--------------------------------------------------+
-| ptep_get_and_clear | Clears a PTE |
+| ptep_clear | Clears a PTE |
+---------------------------+--------------------------------------------------+
-| ptep_get_and_clear_full | Clears a PTE |
+| ptep_get_and_clear | Clears and returns PTE |
++---------------------------+--------------------------------------------------+
+| ptep_get_and_clear_full | Clears and returns PTE (batched PTE unmap) |
+---------------------------+--------------------------------------------------+
| ptep_test_and_clear_young | Clears young from a PTE |
+---------------------------+--------------------------------------------------+
--- a/include/linux/pgtable.h~mm-ptep_clear-page-table-helper
+++ a/include/linux/pgtable.h
@@ -258,6 +258,14 @@ static inline int pmdp_clear_flush_young
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif
+#ifndef __HAVE_ARCH_PTEP_CLEAR
+static inline void ptep_clear(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep)
+{
+ pte_clear(mm, addr, ptep);
+}
+#endif
+
#ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR
static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
unsigned long address,
--- a/mm/debug_vm_pgtable.c~mm-ptep_clear-page-table-helper
+++ a/mm/debug_vm_pgtable.c
@@ -652,7 +652,7 @@ static void __init pte_clear_tests(struc
set_pte_at(args->mm, args->vaddr, args->ptep, pte);
flush_dcache_page(page);
barrier();
- pte_clear(args->mm, args->vaddr, args->ptep);
+ ptep_clear(args->mm, args->vaddr, args->ptep);
pte = ptep_get(args->ptep);
WARN_ON(!pte_none(pte));
}
--- a/mm/khugepaged.c~mm-ptep_clear-page-table-helper
+++ a/mm/khugepaged.c
@@ -756,11 +756,7 @@ static void __collapse_huge_page_copy(pt
* ptl mostly unnecessary.
*/
spin_lock(ptl);
- /*
- * paravirt calls inside pte_clear here are
- * superfluous.
- */
- pte_clear(vma->vm_mm, address, _pte);
+ ptep_clear(vma->vm_mm, address, _pte);
spin_unlock(ptl);
}
} else {
@@ -774,11 +770,7 @@ static void __collapse_huge_page_copy(pt
* inside page_remove_rmap().
*/
spin_lock(ptl);
- /*
- * paravirt calls inside pte_clear here are
- * superfluous.
- */
- pte_clear(vma->vm_mm, address, _pte);
+ ptep_clear(vma->vm_mm, address, _pte);
page_remove_rmap(src_page, false);
spin_unlock(ptl);
free_page_and_swap_cache(src_page);
_
Patches currently in -mm which might be from pasha.tatashin@xxxxxxxxxx are
mm-ptep_clear-page-table-helper.patch
mm-page-table-check.patch
x86-mm-add-x86_64-support-for-page-table-check.patch
