arm64: split linear and kernel mappings

Quoted 106 lines · Matthias Brugger

Hi Ard,

Quoted 78 lines · Ard Biesheuvel

At the request of Catalin, this series has been split off from my series 'arm64: implement support for KASLR v4' [1]. This sub-series deals with moving the kernel out of the linear mapping into the vmalloc area. This is a prerequisite for independent physical and virtual randomization of the kernel image. On top of that, considering that these changes allow the linear mapping to start at an arbitrary offset above PAGE_OFFSET, it should be an improvement in itself due to the fact that we can now choose PAGE_OFFSET such that RAM can be mapped using large block sizes.

For instance, on my Seattle A0 box, the kernel is loaded 16 MB into the lowest GB of RAM, which means __pa(PAGE_OFFSET) is not 1 GB aligned, and the entire 16 GB of RAM will be mapping using 2 MB blocks. (Similarly, for 64 KB granule kernels, the entire 16 GB of RAM will be mapped using pages since __pa(PAGE_OFFSET) is not 512 MB aligned). With these changes
__pa(PAGE_OFFSET) will always be chosen such that it is aligned to a
quantity that allows efficient mapping.

Note that of the entire KASLR series, this sub-series is the most likely to
cause problems, and hence requires the most careful review and testing. This
is due to the fact that, with these changes, the invariant __va(__pa(x)) == x
no longer holds, and any code that is based on that assumption needs to be updated.

Changes since v4:
- added Marc's ack to patch #6
- round the kasan zero shadow region around the kernel image to swapper block

    size (#7)

- ensure that we don't clip the kernel image when clipping RAM to the linear
region size (#8)

Patch #1 allows the low mark of memblocks discovered from the FDT to be overridden by the architecture.

Patch #2 enables the huge-vmap generic feature for arm64. This should be an
improvement in itself, but the significance for this series is that it allows
unmap_kernel_range() to be called on the [__init_begin, __init_end) region,
which may be partially mapped using block mappings.

Patch #3 introduces KIMAGE_VADDR as a separate, preparatory step towards decoupling the kernel placement from PAGE_OFFSET

Patch #4 implements some translation table accessors that operate on statically
allocate translation tables before the linear mapping is up.

Patch #5 decouples the fixmap initialization from the linear mapping, by using
the accessors implemented by patch #4

Patch #6 removes assumptions made my KVM regarding the placement of the kernel
image inside the linear mapping.

Patch #7 moves the kernel image from the base of the linear mapping to the base
of the vmalloc area. The modules area, which sits right below the kernel image,
is moved along and is put right before the start of the vmalloc area.

Patch #8 decouples PHYS_OFFSET from PAGE_OFFSET, which allows the linear mapping
to cover all discovered memory, regardless of where the kernel image is located
in it. This effectively allows the kernel to be loaded at any physical address
(provided that the correct alignment is used)

[1] http://thread.gmane.org/gmane.linux.kernel/2135931

Quoted 10 lines

Ard Biesheuvel (8):
of/fdt: make memblock minimum physical address arch configurable
arm64: add support for ioremap() block mappings
arm64: introduce KIMAGE_VADDR as the virtual base of the kernel region
arm64: pgtable: implement static [pte|pmd|pud]_offset variants
arm64: decouple early fixmap init from linear mapping
arm64: kvm: deal with kernel symbols outside of linear mapping
arm64: move kernel image to base of vmalloc area
arm64: allow kernel Image to be loaded anywhere in physical memory

I bisected linux-next (20160212) with the following error on booting with an initramfs:
Failed to execute /init (error -8)
request_module: runaway loop modprobe binfmt-464c
Starting init: /sbin/init exists but couldn't execute it (error -8)
request_module: runaway loop modprobe binfmt-464c
Starting init: /bin/sh exists but couldn't execute it (error -8)

  Kernel panic - not syncing: No working init found.  Try passing init=

option to kernel. See Linux Documentation/init..

I tracked down the error to patch 7 of this series. But I realized that patch 7 does not compile, but from patch 8 onwards I observe the error.

Quoted 4 lines

I use defconfig with an initramfs.cpio created with buildroot. I tested this on my mt8173 eval board, but I suppose this can be reproduced easily on other machines as well.

Thanks for the report. Does this help at all?

http://thread.gmane.org/gmane.linux.ports.arm.kernel/477645

Quoted 30 lines

Regards,
Matthias

Quoted 25 lines

   Documentation/arm64/booting.txt                      |  20 ++-
   Documentation/features/vm/huge-vmap/arch-support.txt |   2 +-
   arch/arm/include/asm/kvm_asm.h                       |   2 +
   arch/arm/kvm/arm.c                                   |   8 +-
   arch/arm64/Kconfig                                   |   1 +
   arch/arm64/include/asm/boot.h                        |   6 +
   arch/arm64/include/asm/kasan.h                       |   2 +-
   arch/arm64/include/asm/kernel-pgtable.h              |  12 ++
   arch/arm64/include/asm/kvm_asm.h                     |   2 +
   arch/arm64/include/asm/kvm_host.h                    |   8 +-
   arch/arm64/include/asm/memory.h                      |  44 ++++--
   arch/arm64/include/asm/pgtable.h                     |  23 ++-
   arch/arm64/kernel/head.S                             |   8 +-
   arch/arm64/kernel/image.h                            |  13 +-
   arch/arm64/kernel/vmlinux.lds.S                      |   4 +-
   arch/arm64/kvm/hyp.S                                 |   6 +-
   arch/arm64/mm/dump.c                                 |  12 +-
   arch/arm64/mm/init.c                                 | 123
++++++++++++++--
   arch/arm64/mm/kasan_init.c                           |  31 +++-
   arch/arm64/mm/mmu.c                                  | 155
+++++++++++++++-----
   drivers/of/fdt.c                                     |   5 +-
   21 files changed, 378 insertions(+), 109 deletions(-)