[PATCH v5 00/21] arm64: refactor boot flow

Ard Biesheuvel
2022-06-24T15:08:32Z

This series aims to streamline the boot flow with respect to cache
maintenance and redundant copying of data in memory.

Additionally, this series removes the little dance we do to create a
kernel mapping, relocate the kernel, run the KASLR init code, tear down
the old mapping and create a new one, relocate the kernel again, and
finally enter the kernel proper. Instead, it invokes a minimal C
function 'kaslr_early_init()' while running from the ID map which
includes a temporary mapping of the FDT. This change represents a
substantial chunk of the diffstat, as it requires some work to
instantiate code that can run safely from an arbitrary load address.

Changes since v4:
- drop all patches related to WXN support for the time being
- move assignment of vabits_actual earlier in the boot
- avoid TCR_T0SZ() macro as it is not quite appropriate for calculating
the value of t0sz itself (as opposed to its representation in TCR)
- ensure that module randomization is done before modules may be loaded,
which might we way before init runs (via request_module())

Changes since v3:
- drop changes for entering with the MMU enabled for now;
- reject mmap() and mprotect() calls with PROT_WRITE and PROT_EXEC flags
passed when WXN is in effect; this essentially matches the behavior of
both selinux and PaX, and most distros (including Android) can already
deal with this just fine;
- defer KASLR initialization to an initcall() to the extent possible.
- add Anshuman's ack to a couple of patches

Changes since v2:
- create a separate, initial ID map that is discarded after boot, and
create the permanent ID map from C code using the ordinary memory
mapping code;
- refactor the extended ID map handling, and along with it, simplify the
early memory mapping macros, so that we can deal with an extended ID
map that requires multiple table entries at intermediate levels;
- eliminate all variable assignments with the MMU off from the happy
flow;
- replace temporary FDT mapping in TTBR1 with a FDT mapping in the
initial ID map;
- use read-only attributes for all code mappings, so we can boot with
WXN enabled if we elect to do so.

Changes since v1:
- Remove the dodgy handling of the KASLR seed, which was necessary to
avoid doing two iterations of the setup/teardown of the page tables.
This is now dealt with by creating the TTBR1 page tables while
executing from TTBR0, and so all memory manipulations are still done
with the MMU and caches on.
- Only boot from EFI with the MMU and caches on if the image was not
moved around in memory. Otherwise, we cannot rely on the firmware's ID
map to have created an executable mapping for the copied code.

[0] https://lore.kernel.org/all/20220304175657.2744400-1-ardb@kernel.org/
[1] https://lore.kernel.org/all/20220330154205.2483167-1-ardb@kernel.org/
[2] https://lore.kernel.org/all/20220613144550.3760857-1-ardb@kernel.org/

Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>

Ard Biesheuvel (21):
arm64: head: move kimage_vaddr variable into C file
arm64: mm: make vabits_actual a build time constant if possible
arm64: head: move assignment of idmap_t0sz to C code
arm64: head: drop idmap_ptrs_per_pgd
arm64: head: simplify page table mapping macros (slightly)
arm64: head: switch to map_memory macro for the extended ID map
arm64: head: split off idmap creation code
arm64: kernel: drop unnecessary PoC cache clean+invalidate
arm64: head: pass ID map root table address to __enable_mmu()
arm64: mm: provide idmap pointer to cpu_replace_ttbr1()
arm64: head: add helper function to remap regions in early page tables
arm64: head: cover entire kernel image in initial ID map
arm64: head: use relative references to the RELA and RELR tables
arm64: head: create a temporary FDT mapping in the initial ID map
arm64: idreg-override: use early FDT mapping in ID map
arm64: head: factor out TTBR1 assignment into a macro
arm64: head: populate kernel page tables with MMU and caches on
arm64: head: record CPU boot mode after enabling the MMU
arm64: kaslr: defer initialization to initcall where permitted
arm64: head: avoid relocating the kernel twice for KASLR
arm64: setup: drop early FDT pointer helpers

arch/arm64/include/asm/assembler.h | 31 +-
arch/arm64/include/asm/kernel-pgtable.h | 18 +-
arch/arm64/include/asm/memory.h | 4 +
arch/arm64/include/asm/mmu_context.h | 16 +-
arch/arm64/include/asm/setup.h | 3 -
arch/arm64/kernel/Makefile | 2 +-
arch/arm64/kernel/cpufeature.c | 2 +-
arch/arm64/kernel/head.S | 458 ++++++++------------
arch/arm64/kernel/hyp-stub.S | 4 +-
arch/arm64/kernel/idreg-override.c | 17 +-
arch/arm64/kernel/image-vars.h | 4 +
arch/arm64/kernel/kaslr.c | 149 +------
arch/arm64/kernel/pi/Makefile | 33 ++
arch/arm64/kernel/pi/kaslr_early.c | 112 +++++
arch/arm64/kernel/setup.c | 15 -
arch/arm64/kernel/sleep.S | 1 +
arch/arm64/kernel/suspend.c | 2 +-
arch/arm64/kernel/vmlinux.lds.S | 19 +-
arch/arm64/mm/init.c | 15 +-
arch/arm64/mm/kasan_init.c | 4 +-
arch/arm64/mm/mmu.c | 55 ++-
arch/arm64/mm/proc.S | 10 +-
22 files changed, 505 insertions(+), 469 deletions(-)
create mode 100644 arch/arm64/kernel/pi/Makefile
create mode 100644 arch/arm64/kernel/pi/kaslr_early.c