[v2,0/4] page table check

Message

Pasha Tatashin Dec. 4, 2021, 6:23 p.m. UTC

Changelog:
v2:
- Fixed bug reported by Fushan Wen
  The root cause was that in do_swap_page() we first add page table entry
  and only later change its type to anon.
- Added EXPORT_SYMBOL() to functions which are called from set_pte_* type
  functions.
- Replaced DEFINE_STATIC_KEY_TRUE_RO with DEFINE_STATIC_KEY_TRUE to fix
  issue with module load/unload as reported and root caused by Jiri Slaby

v1:
- Added ptep_clear() to mm/debug_vm_pgtable.c (thanks Anshuman Khandual)
- Addressed documentation comments from Jonathan Corbet.

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/[e-mail]
[2] https://lore.kernel.org/all/[e-mail]
[3] https://lore.kernel.org/all/[e-mail]
[4] https://lore.kernel.org/all/[e-mail]

Previous versions:
v1: https://lore.kernel.org/all/[e-mail]/
RFC: https://lore.kernel.org/all/[e-mail]

Pasha Tatashin (4):
  mm: change page type prior to adding page table entry
  mm: ptep_clear() page table helper
  mm: page table check
  x86: mm: add x86_64 support for page table check

 Documentation/vm/arch_pgtable_helpers.rst |   6 +-
 Documentation/vm/index.rst                |   1 +
 Documentation/vm/page_table_check.rst     |  56 +++++
 MAINTAINERS                               |   9 +
 arch/Kconfig                              |   3 +
 arch/x86/Kconfig                          |   1 +
 arch/x86/include/asm/pgtable.h            |  29 ++-
 include/linux/page_table_check.h          | 147 ++++++++++++
 include/linux/pgtable.h                   |   8 +
 mm/Kconfig.debug                          |  24 ++
 mm/Makefile                               |   1 +
 mm/debug_vm_pgtable.c                     |   2 +-
 mm/khugepaged.c                           |  12 +-
 mm/memory.c                               |   7 +-
 mm/page_alloc.c                           |   4 +
 mm/page_ext.c                             |   4 +
 mm/page_table_check.c                     | 270 ++++++++++++++++++++++
 17 files changed, 566 insertions(+), 18 deletions(-)
 create mode 100644 Documentation/vm/page_table_check.rst
 create mode 100644 include/linux/page_table_check.h
 create mode 100644 mm/page_table_check.c

Comments

Fushan Wen Dec. 21, 2021, 1:09 p.m. UTC | #1

I can confirm this patch resolved my issue. My system has been running 
three days with page table check enabled and is very stable.

Thank you very much!

Pasha Tatashin Dec. 21, 2021, 2:48 p.m. UTC | #2

Hi Fushan,

On Tue, Dec 21, 2021 at 8:09 AM Fusion Future <[e-mail]> wrote:
>
> I can confirm this patch resolved my issue. My system has been running
> three days with page table check enabled and is very stable.

Thank you for testing!

Pasha