[PATCH v6sub1 00/11] arm64: split linear and kernel mappings

[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 mapped 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.

The complete series can be found here:
https://git.linaro.org/people/ard.biesheuvel/linux-arm.git/shortlog/refs/heads/arm64-kaslr-v6

Changes since v5 [2]:
- fixed an initrd issue, where __va() was called by the generic early FDT code
  before memstart_addr is assigned (#2, #10)
- add patch #3 to fix a circular header dependency so we can use BUG_ON in
  asm/memory.h
- BUG() if __va() is called before memstart_addr is assigned (#11)
- fix a (transient) issue with GCC 4.9 or older in the KVM ksym ref patch  (#8)
  that affects bisectability (the actual issue surfaces after applying patch #9
  and disappears again with patch #11)
- fix a KASAN problem in the previous version of patch #9, where the shadow
  region of the module area was inadvertently populated with KASAN zero pages;
  this fixes at least one of the reported KASAN related issues with this series
- folded __maybe_unused change into patch #9
- folded change to memblock_add() back the entire kernel image instead of only
  the init and data segments after clipping for mem=
- map the linear alias of [_stext, _etext] as read-only/non-executable so its
  contents are visible to subsystems like hibernate in the expected place (#9)
- folded patch that removed clip_memory_range() and reverted to the generic
  memblock_enforce_memory_limit() (#11)

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 allows the assignment of initrd_start and initrd_end in generic early
FDT code to be overridden by architecture code.

Patch #3 reverses the #include dependencies between asm/bug.h and another
header file so that asm/bug.h can be included (and used) in asm/memory.h

Patch #4 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 #5 introduces KIMAGE_VADDR as a separate, preparatory step towards
decoupling the kernel placement from PAGE_OFFSET

Patch #6 implements some translation table accessors that operate on statically
allocate translation tables before the linear mapping is up.

Patch #7 decouples the fixmap initialization from the linear mapping, by using
the accessors implemented by patch #6

Patch #8 removes assumptions made my KVM regarding the placement of the kernel
image inside the linear mapping.

Patch #9 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 #10 defers the __va translation of the initrd to after the assignment of
memstart_addr.

Patch #11 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
[2] http://thread.gmane.org/gmane.linux.ports.arm.kernel/473894

Ard Biesheuvel (11):
  of/fdt: make memblock minimum physical address arch configurable
  of/fdt: factor out assignment of initrd_start/initrd_end
  arm64: prevent potential circular header dependencies in asm/bug.h
  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: defer __va translation of initrd_start and initrd_end
  arm64: allow kernel Image to be loaded anywhere in physical memory

 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/bug.h                         |   2 +-
 arch/arm64/include/asm/debug-monitors.h              |   2 +-
 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                      |  55 +++++--
 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/kvm/hyp/debug-sr.c                        |   1 +
 arch/arm64/mm/dump.c                                 |  12 +-
 arch/arm64/mm/init.c                                 |  99 ++++++++++--
 arch/arm64/mm/kasan_init.c                           |  27 +++-
 arch/arm64/mm/mmu.c                                  | 168 +++++++++++++++-----
 drivers/of/fdt.c                                     |  19 ++-
 24 files changed, 381 insertions(+), 121 deletions(-)

-- 
2.5.0