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Subject: Re: [PATCH v7 00/12] implement KASLR for powerpc/fsl_booke/32
From:   Jason Yan <yanaijie@huawei.com>
To:     <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>, <zhaohongjiang@huawei.com>
References: <20190920094546.44948-1-yanaijie@huawei.com>
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Message-ID: <c4769b34-95f6-81b9-4856-50459630aa0d@huawei.com>
Date:   Wed, 9 Oct 2019 14:10:27 +0800
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Hi Scott,

Would you please take sometime to test this?

Thank you so much.

On 2019/9/24 13:52, Jason Yan wrote:
> 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
>>
> 
> 
> .
>