[RFC 0/3] page table check

[Pasha Tatashin <pasha.tatashin@soleen.com>]

From: Pasha Tatashin <tatashin@google.com>

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@gthelen2.svl.corp.google.com
[2] https://lore.kernel.org/all/1582661774-30925-2-git-send-email-akaher@vmware.com
[3] https://lore.kernel.org/all/20210622021423.154662-3-mike.kravetz@oracle.com
[4] https://lore.kernel.org/all/20211026173822.502506-1-pasha.tatashin@soleen.com

Pasha Tatashin (3):
  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/page_table_check.rst     |  53 +++++
 MAINTAINERS                               |   9 +
 arch/Kconfig                              |   3 +
 arch/x86/Kconfig                          |   1 +
 arch/x86/include/asm/pgtable.h            |  27 ++-
 include/linux/page_table_check.h          | 147 ++++++++++++
 include/linux/pgtable.h                   |   8 +
 mm/Kconfig.debug                          |  24 ++
 mm/Makefile                               |   1 +
 mm/khugepaged.c                           |  12 +-
 mm/page_alloc.c                           |   4 +
 mm/page_ext.c                             |   4 +
 mm/page_table_check.c                     | 264 ++++++++++++++++++++++
 14 files changed, 549 insertions(+), 14 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

-- 
2.34.0.rc1.387.gb447b232ab-goog