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Message-ID: <d20088d2-f993-1d7c-7474-3e41c3b34d45@huawei.com>
Date: Thu, 8 Aug 2019 11:19:42 +0800
From: Jason Yan <yanaijie@...wei.com>
To: Michael Ellerman <mpe@...erman.id.au>, <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>
Subject: Re: [PATCH v5 00/10] implement KASLR for powerpc/fsl_booke/32
On 2019/8/7 21:12, Michael Ellerman wrote:
> 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.
>
Thank you. I will try my best to improve the code.
> 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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