forked from Minki/linux
ee65728e10
so it will be consistent with code mm directory and with Documentation/admin-guide/mm and won't be confused with virtual machines. Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Suggested-by: Matthew Wilcox <willy@infradead.org> Tested-by: Ira Weiny <ira.weiny@intel.com> Acked-by: Jonathan Corbet <corbet@lwn.net> Acked-by: Wu XiangCheng <bobwxc@email.cn>
57 lines
2.4 KiB
ReStructuredText
57 lines
2.4 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
.. _page_table_check:
|
|
|
|
================
|
|
Page Table Check
|
|
================
|
|
|
|
Introduction
|
|
============
|
|
|
|
Page table check allows to harden the kernel by ensuring that some types of
|
|
the memory corruptions are prevented.
|
|
|
|
Page table check performs extra verifications at the time when new pages become
|
|
accessible from the userspace by getting their page table entries (PTEs PMDs
|
|
etc.) added into the table.
|
|
|
|
In case of detected corruption, the kernel is crashed. There is a small
|
|
performance and memory overhead associated with the page table check. Therefore,
|
|
it is disabled by default, but can be optionally enabled on systems where the
|
|
extra hardening outweighs the performance costs. Also, because page table check
|
|
is synchronous, it can help with debugging double map memory corruption issues,
|
|
by crashing kernel at the time wrong mapping occurs instead of later which is
|
|
often the case with memory corruptions bugs.
|
|
|
|
Double mapping detection logic
|
|
==============================
|
|
|
|
+-------------------+-------------------+-------------------+------------------+
|
|
| Current Mapping | New mapping | Permissions | Rule |
|
|
+===================+===================+===================+==================+
|
|
| Anonymous | Anonymous | Read | Allow |
|
|
+-------------------+-------------------+-------------------+------------------+
|
|
| Anonymous | Anonymous | Read / Write | Prohibit |
|
|
+-------------------+-------------------+-------------------+------------------+
|
|
| Anonymous | Named | Any | Prohibit |
|
|
+-------------------+-------------------+-------------------+------------------+
|
|
| Named | Anonymous | Any | Prohibit |
|
|
+-------------------+-------------------+-------------------+------------------+
|
|
| Named | Named | Any | Allow |
|
|
+-------------------+-------------------+-------------------+------------------+
|
|
|
|
Enabling Page Table Check
|
|
=========================
|
|
|
|
Build kernel with:
|
|
|
|
- PAGE_TABLE_CHECK=y
|
|
Note, it can only be enabled on platforms where ARCH_SUPPORTS_PAGE_TABLE_CHECK
|
|
is available.
|
|
|
|
- Boot with 'page_table_check=on' kernel parameter.
|
|
|
|
Optionally, build kernel with PAGE_TABLE_CHECK_ENFORCED in order to have page
|
|
table support without extra kernel parameter.
|