linux-kernel - [RFC][PATCH 0/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions if existed

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Date:   Thu, 15 Jun 2017 15:52:47 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     keescook@...omium.org, x86@...nel.org, fanc.fnst@...fujitsu.com,
        caoj.fnst@...fujitsu.com, douly.fnst@...fujitsu.com,
        Baoquan He <bhe@...hat.com>
Subject: [RFC][PATCH 0/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions if existed

Our customer reported that Kernel text may be located on non-mirror
region (movable zone) when both address range mirroring feature and
KASLR are enabled.

The functions of address range mirroring feature are as follows.
- The physical memory region whose descriptors in EFI memory map have
  EFI_MEMORY_MORE_RELIABLE attribute (bit: 16) are mirrored
- The function arranges such mirror region into normal zone and other region
  into movable zone in order to locate kernel code and data on mirror region

So we need restrict kernel to be located inside mirror region if it
is existed.

The method is very simple. If efi is enabled, just iterate all efi
memory map and pick up mirror region to process for adding candidate
of slot. If efi disabled or no mirror region existed, still process
e820 memory map. This won't bring much efficiency loss, at worst we
just go through all efi memory maps and found no mirror.

One question:
>From code, though mirror regions are existed, they are meaningful only
if kernelcore=mirror kernel option is specified. Not sure if my understanding
is correct.

NOTE:
I haven't got a machine with efi mirror region enabled, so only test the
e820 map processing case and the case of no mirror region on efi machine.
So set this as a RFC patchset, will post formal one after above question
is made clear and mirror issue test passed.

Baoquan He (2):
  x86/boot/KASLR: Adapt process_e820_entry for all kinds of memory map
  x86/boot/KASLR: Restrict kernel to be randomized in mirror regions if
    existed

 arch/x86/boot/compressed/kaslr.c | 129 +++++++++++++++++++++++++++++++--------
 1 file changed, 104 insertions(+), 25 deletions(-)

-- 
2.5.5