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Message-ID: <87tvatt8z2.fsf@concordia.ellerman.id.au>
Date: Wed, 07 Aug 2019 23:12:49 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Jason Yan <yanaijie@...wei.com>, linuxppc-dev@...ts.ozlabs.org, diana.craciun@....com, christophe.leroy@....fr, benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com, keescook@...omium.org, kernel-hardening@...ts.openwall.com, oss@...error.net
Cc: linux-kernel@...r.kernel.org, wangkefeng.wang@...wei.com, yebin10@...wei.com, thunder.leizhen@...wei.com, jingxiangfeng@...wei.com, fanchengyang@...wei.com, zhaohongjiang@...wei.com, Jason Yan <yanaijie@...wei.com>
Subject: Re: [PATCH v5 00/10] implement KASLR for powerpc/fsl_booke/32
Hi Jason,
Jason Yan <yanaijie@...wei.com> 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
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