[v7,0/3] x86/boot/KASLR: Parse ACPI table and limit kaslr in immovable memory

Message

Chao Fan Sept. 13, 2018, 10:46 a.m. UTC

***Background:
People reported that kaslr may randomly chooses some positions
which are located in movable memory regions. This will break memory
hotplug feature and make the movable memory chosen by KASLR can't be
removed.

***Solutions:
There should be a method to limit kaslr to choosing immovable memory
regions, so there are 2 solutions:
1) Add a kernel parameter to specify the memory regions.
2) Get the information of memory hot-remove, then kaslr will know the
   right regions.
In method 2, information about memory hot-remove is in ACPI
tables, which will be parsed after start_kernel(), kaslr can't get
the information.
In method 1, users should know the regions address and specify in
kernel parameter.

In the earliest time, I tried to dig ACPI tabls to solve this problem.
But I didn't splite the code in 'compressed/' and ACPI code, so the patch
is hard to follow so refused by community.
Somebody suggest to add a kernel parameter to specify the
immovable memory so that limit kaslr in these regions. Then I make
a new patchset. After several versions, Ingo gave a suggestion:
https://www.mail-archive.com/[e-mail]/msg1634024.html
Follow Ingo's suggestion, imitate the ACPI code to parse the acpi
tables, so that the kaslr can get necessary memory information in
ACPI tables.
I think ACPI code is an independent part, so copy the codes
and functions to 'compressed/' directory, so that kaslr won't
influence the initialization of ACPI.

PATCH 1/3 Add acpitb.c to provide functions to parse ACPI code.
PATCH 2/3 If CONFIG_MEMORY_HOTREMOVE enabled, walk all nodes and
          store the information of immovable memory regions.
PATCH 3/3 According to the immovable memory regions, filter the
          immovable regions which KASLR can choose.

***Test results:
 - I did a very simple test, and it can get the memory information in
   bios and efi KVM guest machine, and put it by early printk. But no
   more tests, so it's with RFC tag.

v1->v2:
 -  Simplify some code.
Follow Baoquan He's suggestion:
 - Reuse the head file of acpi code.

v2->v3:
 - Test in more conditions, so remove the 'RFC' tag.
 - Change some comments.

v3->v4:
Follow Thomas Gleixner's suggetsion:
 - Put the whole efi related function into #define CONFIG_EFI and return
   false in the other stub.
 - Simplify two functions in head file.

v4->v5:
Follow Dou Liyang's suggestion:
 - Add more comments about some functions based on kernel code.
 - Change some typo in comments.
 - Clean useless variable.
 - Add check for the boundary of array.
 - Add check for 'movable_node' parameter

v5->v6:
Follow Baoquan He's suggestion:
 - Change some log.
 - Add the check for acpi_rsdp
 - Change some code logical to make code clear

v6->v7:
Follow Rafael's suggestion:
 - Add more comments and patch log.
Follow test robot's suggestion:
 - Add "static" tag for function

Any comments will be welcome.


Chao Fan (3):
  x86/boot: Add acpitb.c to parse acpi tables
  x86/boot/KASLR: Walk srat tables to filter immovable memory
  x86/boot/KASLR: Limit kaslr to choosing the immovable memory

 arch/x86/boot/compressed/Makefile |   4 +
 arch/x86/boot/compressed/acpitb.c | 401 ++++++++++++++++++++++++++++++
 arch/x86/boot/compressed/kaslr.c  |  76 +++++-
 arch/x86/boot/compressed/misc.h   |   8 +
 4 files changed, 478 insertions(+), 11 deletions(-)
 create mode 100644 arch/x86/boot/compressed/acpitb.c