[PATCH v5sub1 0/8] arm64: split linear and kernel mappings
Ard Biesheuvel
ard.biesheuvel at linaro.org
Sat Feb 13 06:28:25 PST 2016
On 12 February 2016 at 21:10, Matthias Brugger <matthias.bgg at gmail.com> wrote:
>
>
> On 12/02/16 20:47, Ard Biesheuvel wrote:
>>
>> 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.
>>>
As far as this failure is concerned, I managed to reproduce an error
with patch #7 and not #8 applied, involving out of range kvm symbols
at link time. This is reproducible with GCC 4.8 but not GCC 4.9 or
later. Is this what you were seeing as well? Or is there another
problem?
>>> 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
>>
>
> I applied them on top of linux-next and this fixed the problem.
>
> Thanks,
> Matthias
>
>
>>> 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(-)
>>>>
>>>
>
More information about the linux-arm-kernel
mailing list