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author | Mike Rapoport <rppt@linux.ibm.com> | 2022-06-27 09:00:26 +0300 |
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committer | akpm <akpm@linux-foundation.org> | 2022-06-27 22:52:53 +0300 |
commit | ee65728e103bb7dd99d8604bf6c7aa89c7d7e446 (patch) | |
tree | 356a37c67d23c69cf8de83120d08048276cb5bfc /Documentation/mm/page_table_check.rst | |
parent | 46a3b1125308f8f90a065eeecfafd2a96b01a36c (diff) | |
download | linux-ee65728e103bb7dd99d8604bf6c7aa89c7d7e446.tar.xz |
docs: rename Documentation/vm to Documentation/mm
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>
Diffstat (limited to 'Documentation/mm/page_table_check.rst')
-rw-r--r-- | Documentation/mm/page_table_check.rst | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/Documentation/mm/page_table_check.rst b/Documentation/mm/page_table_check.rst new file mode 100644 index 000000000000..1a09472f10a3 --- /dev/null +++ b/Documentation/mm/page_table_check.rst @@ -0,0 +1,56 @@ +.. 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. |