linux-kernel - [PATCH v3 0/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

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Message-Id: <1499241974-7938-1-git-send-email-bhe@redhat.com>
Date:   Wed,  5 Jul 2017 16:06:12 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, tglx@...utronix.de, hpa@...or.com,
        mingo@...nel.org, keescook@...omium.org, izumi.taku@...fujitsu.com,
        thgarnie@...gle.com, fanc.fnst@...fujitsu.com,
        matt@...eblueprint.co.uk, Baoquan He <bhe@...hat.com>
Subject: [PATCH v3 0/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

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 regions if it
is existed.

The method is very simple. If efi is enabled, just iterate all efi
memory map and pick 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.

Changelog:
v2->v3:
  Put process_efi_entry invocation inside the #ifdef CONFIG_EFI according
  to tglx's suggestion. Since the efi related code is meaningful only if
  CONFIG_EFI=y.

v1->v2:
  Removed debug code.

  Taku suggested that we should put kernel to mirrored region always
  whether or not "kernelcore=mirror" is specified since kernel text is
  important and mirrored region is reliable.

  Change code according to kbuild report and Chao Fan's comment.

Test:
Chao helped testing the v1 (RFC patchset) 100 times. And he said in the 100
times, 50 times are with this patchset applied, 50 times are without it.
The test result showed the v1 patchset works very well.

Baoquan He (2):
  x86/boot/KASLR: Adapt process_e820_entry for any type of memory entry
  x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

 arch/x86/boot/compressed/kaslr.c | 108 +++++++++++++++++++++++++++++----------
 1 file changed, 82 insertions(+), 26 deletions(-)

-- 
2.5.5