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[RFC PATCH 0/4] x86/boot/KASLR: Parse ACPI table and limit kaslr in immovable memory.




***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 memory 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 hotremove, then kaslr will know the
   right regions.
But 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 patchset. After several versions, Ingo gave a suggestion:
https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/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.
Since I think ACPI code is independent part, so copy the codes
and functions to 'compressed/' directory, so that kaslr won't
influence the initialization of ACPI.

*** Issues need be discussed
There are several issues I am not quite sure, please help review and
give suggestions:

1) In PATCH 1, I copy the structures and functions from ACPI head file,
   so that ACPI head file will never been used here. I am not sure
   whether it's good to include ACPI head file or use the method in
   PATCH 1. If people think we can use ACPI head files directely, I
   will remove the PATCH 1.

***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.

Any comments will be welcome.


Chao Fan (4):
  x86/boot: Add acpitb.h to help parse acpi tables
  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 |   1 +
 arch/x86/boot/compressed/acpitb.c | 245 ++++++++++++++++++++++++++++++
 arch/x86/boot/compressed/acpitb.h | 175 +++++++++++++++++++++
 arch/x86/boot/compressed/kaslr.c  | 120 +++++++++++++--
 4 files changed, 530 insertions(+), 11 deletions(-)
 create mode 100644 arch/x86/boot/compressed/acpitb.c
 create mode 100644 arch/x86/boot/compressed/acpitb.h

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2.17.0