Re: [PATCH v7 00/12] implement KASLR for powerpc/fsl_booke/32

[Jason Yan <yanaijie@huawei.com>]

Hi Scott,

Can you test v7 to see if it works to load a kernel at a non-zero address?

Thanks,

On 2019/9/20 17:45, Jason Yan wrote:
> 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.
> 
> 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    <-----|
> 
>                                kernstart_virt_addr
> 
> 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 v6:
>   - Rename create_tlb_entry() to create_kaslr_tlb_entry()
>   - Remove MAS2_VAL since there is no more users.
>   - Move kaslr_booke.c to arch/powerpc/mm/nohash.
>   - Call flush_icache_range() after copying the kernel.
>   - Warning if no kaslr-seed provided by the bootloader
>   - Use the right physical address when checking if the new position will overlap with other regions.
>   - Do not clear bss for the second pass because some global variables will not be initialized again
>   - Use tabs instead of spaces between the mnemonic and the arguments(in fsl_booke_entry_mapping.S).
> 
> Changes since v5:
>   - Rename M_IF_NEEDED to MAS2_M_IF_NEEDED
>   - Define some global variable as __ro_after_init
>   - Replace kimage_vaddr with kernstart_virt_addr
>   - Depend on RELOCATABLE, not select it
>   - Modify the comment block below the SPDX tag
>   - Remove some useless headers in kaslr_booke.c and move is_second_reloc
>     declarationto mmu_decl.h
>   - Remove DBG() and use pr_debug() and rewrite comment above get_boot_seed().
>   - Add a patch to document the KASLR implementation.
>   - Split a patch from patch #10 which exports kaslr offset in VMCOREINFO ELF notes.
>   - Remove extra logic around finding nokaslr string in cmdline.
>   - Make regions static global and __initdata
> 
> 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 (12):
>    powerpc: unify definition of M_IF_NEEDED
>    powerpc: move memstart_addr and kernstart_addr to init-common.c
>    powerpc: introduce kernstart_virt_addr to store the kernel base
>    powerpc/fsl_booke/32: introduce create_kaslr_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
>    powerpc/fsl_booke/kaslr: export offset in VMCOREINFO ELF notes
>    powerpc/fsl_booke/32: Document KASLR implementation
> 
>   Documentation/powerpc/kaslr-booke32.rst       |  42 ++
>   arch/powerpc/Kconfig                          |  11 +
>   arch/powerpc/include/asm/nohash/mmu-book3e.h  |  11 +-
>   arch/powerpc/include/asm/page.h               |   7 +
>   arch/powerpc/kernel/early_32.c                |   5 +-
>   arch/powerpc/kernel/exceptions-64e.S          |  12 +-
>   arch/powerpc/kernel/fsl_booke_entry_mapping.S |  25 +-
>   arch/powerpc/kernel/head_fsl_booke.S          |  61 ++-
>   arch/powerpc/kernel/machine_kexec.c           |   1 +
>   arch/powerpc/kernel/misc_64.S                 |   7 +-
>   arch/powerpc/kernel/setup-common.c            |  20 +
>   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                    |  11 +
>   arch/powerpc/mm/nohash/Makefile               |   1 +
>   arch/powerpc/mm/nohash/fsl_booke.c            |   8 +-
>   arch/powerpc/mm/nohash/kaslr_booke.c          | 401 ++++++++++++++++++
>   18 files changed, 587 insertions(+), 53 deletions(-)
>   create mode 100644 Documentation/powerpc/kaslr-booke32.rst
>   create mode 100644 arch/powerpc/mm/nohash/kaslr_booke.c
>