[PATCH v5sub1 0/8] arm64: split linear and kernel mappings

[Ard Biesheuvel]

On 12 February 2016 at 20:45, Matthias Brugger <matthias.bgg at gmail.com> wrote:
> Hi Ard,
>
>
> On 01/02/16 11:54, Ard Biesheuvel wrote:
>>
>> 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
>>
>> 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.
>
> 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

> Regards,
> Matthias
>
>
>>   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(-)
>>
>