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

From: Jason Yan <yanaijie@huawei.com>
To: Michael Ellerman <mpe@ellerman.id.au>,
	<linuxppc-dev@lists.ozlabs.org>, <diana.craciun@nxp.com>,
	<christophe.leroy@c-s.fr>, <benh@kernel.crashing.org>,
	<paulus@samba.org>, <npiggin@gmail.com>, <keescook@chromium.org>,
	<kernel-hardening@lists.openwall.com>, <oss@buserror.net>
Cc: <linux-kernel@vger.kernel.org>, <wangkefeng.wang@huawei.com>,
	<yebin10@huawei.com>, <thunder.leizhen@huawei.com>,
	<jingxiangfeng@huawei.com>, <fanchengyang@huawei.com>,
	<zhaohongjiang@huawei.com>
Subject: Re: [PATCH v5 00/10] implement KASLR for powerpc/fsl_booke/32
Date: Thu, 8 Aug 2019 11:19:42 +0800	[thread overview]
Message-ID: <d20088d2-f993-1d7c-7474-3e41c3b34d45@huawei.com> (raw)
In-Reply-To: <87tvatt8z2.fsf@concordia.ellerman.id.au>

On 2019/8/7 21:12, Michael Ellerman wrote:
> Hi Jason,
> 
> Jason Yan <yanaijie@huawei.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
> 
> .
> 