Re: [PATCH v5 00/10] implement KASLR for powerpc/fsl_booke/32

[Michael Ellerman]

Hi Jason,

Jason Yan <yanaijie@xxxxxxxxxx> writes:
> This series implements KASLR for powerpc/fsl_booke/32, as a security
> feature that deters exploit attempts relying on knowledge of the location
> of kernel internals.

Thanks for doing this work.

Sorry I didn't get a chance to look at this until v5, I sent a few
comments just now. Nothing major though, I think this looks almost ready
to merge.

cheers

> Since CONFIG_RELOCATABLE has already supported, what we need to do is
> map or copy kernel to a proper place and relocate. Freescale Book-E
> parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1
> entries are not suitable to map the kernel directly in a randomized
> region, so we chose to copy the kernel to a proper place and restart to
> relocate.
>
> Entropy is derived from the banner and timer base, which will change every
> build and boot. This not so much safe so additionally the bootloader may
> pass entropy via the /chosen/kaslr-seed node in device tree.
>
> We will use the first 512M of the low memory to randomize the kernel
> image. The memory will be split in 64M zones. We will use the lower 8
> bit of the entropy to decide the index of the 64M zone. Then we chose a
> 16K aligned offset inside the 64M zone to put the kernel in.
>
>     KERNELBASE
>
>         |-->   64M   <--|
>         |               |
>         +---------------+    +----------------+---------------+
>         |               |....|    |kernel|    |               |
>         +---------------+    +----------------+---------------+
>         |                         |
>         |----->   offset    <-----|
>
>                               kimage_vaddr
>
> We also check if we will overlap with some areas like the dtb area, the
> initrd area or the crashkernel area. If we cannot find a proper area,
> kaslr will be disabled and boot from the original kernel.
>
> Changes since v4:
>  - Add Reviewed-by tag from Christophe
>  - Remove an unnecessary cast
>  - Remove unnecessary parenthesis
>  - Fix checkpatch warning
>
> Changes since v3:
>  - Add Reviewed-by and Tested-by tag from Diana
>  - Change the comment in fsl_booke_entry_mapping.S to be consistent
>    with the new code.
>
> Changes since v2:
>  - Remove unnecessary #ifdef
>  - Use SZ_64M instead of0x4000000
>  - Call early_init_dt_scan_chosen() to init boot_command_line
>  - Rename kaslr_second_init() to kaslr_late_init()
>
> Changes since v1:
>  - Remove some useless 'extern' keyword.
>  - Replace EXPORT_SYMBOL with EXPORT_SYMBOL_GPL
>  - Improve some assembly code
>  - Use memzero_explicit instead of memset
>  - Use boot_command_line and remove early_command_line
>  - Do not print kaslr offset if kaslr is disabled
>
> Jason Yan (10):
>   powerpc: unify definition of M_IF_NEEDED
>   powerpc: move memstart_addr and kernstart_addr to init-common.c
>   powerpc: introduce kimage_vaddr to store the kernel base
>   powerpc/fsl_booke/32: introduce create_tlb_entry() helper
>   powerpc/fsl_booke/32: introduce reloc_kernel_entry() helper
>   powerpc/fsl_booke/32: implement KASLR infrastructure
>   powerpc/fsl_booke/32: randomize the kernel image offset
>   powerpc/fsl_booke/kaslr: clear the original kernel if randomized
>   powerpc/fsl_booke/kaslr: support nokaslr cmdline parameter
>   powerpc/fsl_booke/kaslr: dump out kernel offset information on panic
>
>  arch/powerpc/Kconfig                          |  11 +
>  arch/powerpc/include/asm/nohash/mmu-book3e.h  |  10 +
>  arch/powerpc/include/asm/page.h               |   7 +
>  arch/powerpc/kernel/Makefile                  |   1 +
>  arch/powerpc/kernel/early_32.c                |   2 +-
>  arch/powerpc/kernel/exceptions-64e.S          |  10 -
>  arch/powerpc/kernel/fsl_booke_entry_mapping.S |  27 +-
>  arch/powerpc/kernel/head_fsl_booke.S          |  55 ++-
>  arch/powerpc/kernel/kaslr_booke.c             | 427 ++++++++++++++++++
>  arch/powerpc/kernel/machine_kexec.c           |   1 +
>  arch/powerpc/kernel/misc_64.S                 |   5 -
>  arch/powerpc/kernel/setup-common.c            |  19 +
>  arch/powerpc/mm/init-common.c                 |   7 +
>  arch/powerpc/mm/init_32.c                     |   5 -
>  arch/powerpc/mm/init_64.c                     |   5 -
>  arch/powerpc/mm/mmu_decl.h                    |  10 +
>  arch/powerpc/mm/nohash/fsl_booke.c            |   8 +-
>  17 files changed, 560 insertions(+), 50 deletions(-)
>  create mode 100644 arch/powerpc/kernel/kaslr_booke.c
>
> -- 
> 2.17.2