[v2,0/4] riscv: Introduce KASLR

Message

Alexandre Ghiti March 29, 2023, 5:29 a.m. UTC

The following KASLR implementation allows to randomize the kernel mapping:

- virtually: we expect the bootloader to provide a seed in the device-tree
- physically: only implemented in the EFI stub, it relies on the firmware to
  provide a seed using EFI_RNG_PROTOCOL. arm64 has a similar implementation
  hence the patch 3 factorizes KASLR related functions for riscv to take
  advantage.

The new virtual kernel location is limited by the early page table that only
has one PUD and with the PMD alignment constraint, the kernel can only take
< 512 positions.

Note that the patch "riscv: Use PUD/P4D/PGD pages for the linear
mapping" is necessary to retrieve the memory below the physical kernel
address, so that the EFI stub does not have to try to relocate the kernel
as close as possible to the start of dram.

This patchset is rebased on top of:

riscv: Allow to downgrade paging mode from the command line
(https://patchwork.kernel.org/project/linux-riscv/list/?series=734849)
base-commit-tag: v6.3-rc1

Changes in v2:
  * Rebase on top of 6.3-rc1
  * Add a riscv cache sync after memcpying the kernel
  * Add kaslr_offset implementation for KCOV
  * Add forward declaration to quiet LLVM

Alexandre Ghiti (4):
  riscv: Introduce virtual kernel mapping KASLR
  riscv: Dump out kernel offset information on panic
  arm64: libstub: Move KASLR handling functions to efi-stub-helper.c
  riscv: libstub: Implement KASLR by using generic functions

 arch/riscv/Kconfig                            |  18 +++
 arch/riscv/include/asm/page.h                 |   3 +
 arch/riscv/kernel/image-vars.h                |   1 +
 arch/riscv/kernel/pi/Makefile                 |   2 +-
 arch/riscv/kernel/pi/cmdline_early.c          |  13 ++
 arch/riscv/kernel/pi/fdt_early.c              |  30 ++++
 arch/riscv/kernel/setup.c                     |  25 +++
 arch/riscv/mm/init.c                          |  36 ++++-
 drivers/firmware/efi/libstub/arm64-stub.c     | 111 +------------
 drivers/firmware/efi/libstub/arm64.c          |   5 +
 .../firmware/efi/libstub/efi-stub-helper.c    | 151 ++++++++++++++++++
 drivers/firmware/efi/libstub/efistub.h        |  10 ++
 drivers/firmware/efi/libstub/riscv-stub.c     |  28 ++--
 drivers/firmware/efi/libstub/riscv.c          |   5 +
 14 files changed, 315 insertions(+), 123 deletions(-)
 create mode 100644 arch/riscv/kernel/pi/fdt_early.c