Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64

[Jason Yan <yanaijie@huawei.com>]

Hi Daniel,

在 2020/2/26 15:16, Daniel Axtens 写道:
> Hi Jason,
> 
>> This is a try to implement KASLR for Freescale BookE64 which is based on
>> my earlier implementation for Freescale BookE32:
>> https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=131718
>>
>> The implementation for Freescale BookE64 is similar as BookE32. One
>> difference is that Freescale BookE64 set up a TLB mapping of 1G during
>> booting. Another difference is that ppc64 needs the kernel to be
>> 64K-aligned. So we can randomize the kernel in this 1G mapping and make
>> it 64K-aligned. This can save some code to creat another TLB map at
>> early boot. The disadvantage is that we only have about 1G/64K = 16384
>> slots to put the kernel in.
>>
>>      KERNELBASE
>>
>>            64K                     |--> kernel <--|
>>             |                      |              |
>>          +--+--+--+    +--+--+--+--+--+--+--+--+--+    +--+--+
>>          |  |  |  |....|  |  |  |  |  |  |  |  |  |....|  |  |
>>          +--+--+--+    +--+--+--+--+--+--+--+--+--+    +--+--+
>>          |                         |                        1G
>>          |----->   offset    <-----|
>>
>>                                kernstart_virt_addr
>>
>> I'm not sure if the slot numbers is enough or the design has any
>> defects. If you have some better ideas, I would be happy to hear that.
>>
>> Thank you all.
>>
> 
> Are you making any attempt to hide kernel address leaks in this series?

Yes.

> I've just been looking at the stackdump code just now, and it directly
> prints link registers and stack pointers, which is probably enough to
> determine the kernel base address:
> 
>                    SPs:               LRs:             %pS pointer
> [    0.424506] [c0000000de403970] [c000000001fc0458] dump_stack+0xfc/0x154 (unreliable)
> [    0.424593] [c0000000de4039c0] [c000000000267eec] panic+0x258/0x5ac
> [    0.424659] [c0000000de403a60] [c0000000024d7a00] mount_block_root+0x634/0x7c0
> [    0.424734] [c0000000de403be0] [c0000000024d8100] prepare_namespace+0x1ec/0x23c
> [    0.424811] [c0000000de403c60] [c0000000024d7010] kernel_init_freeable+0x804/0x880
> 
> git grep \\\"REG\\\" arch/powerpc shows a few other uses like this, all
> in process.c or in xmon.
> 

Thanks for reminding this.

> Maybe replacing the REG format string in KASLR mode would be sufficient?
> 

Most archs have removed the address printing when dumping stack. Do we 
really have to print this?

If we have to do this, maybe we can use "%pK" so that they will be 
hidden from unprivileged users.

Thanks,
Jason

> Regards,
> Daniel
> 
> 
>> v2->v3:
>>    Fix build error when KASLR is disabled.
>> v1->v2:
>>    Add __kaslr_offset for the secondary cpu boot up.
>>
>> Jason Yan (6):
>>    powerpc/fsl_booke/kaslr: refactor kaslr_legal_offset() and
>>      kaslr_early_init()
>>    powerpc/fsl_booke/64: introduce reloc_kernel_entry() helper
>>    powerpc/fsl_booke/64: implement KASLR for fsl_booke64
>>    powerpc/fsl_booke/64: do not clear the BSS for the second pass
>>    powerpc/fsl_booke/64: clear the original kernel if randomized
>>    powerpc/fsl_booke/kaslr: rename kaslr-booke32.rst to kaslr-booke.rst
>>      and add 64bit part
>>
>>   .../{kaslr-booke32.rst => kaslr-booke.rst}    | 35 +++++++--
>>   arch/powerpc/Kconfig                          |  2 +-
>>   arch/powerpc/kernel/exceptions-64e.S          | 23 ++++++
>>   arch/powerpc/kernel/head_64.S                 | 14 ++++
>>   arch/powerpc/kernel/setup_64.c                |  4 +-
>>   arch/powerpc/mm/mmu_decl.h                    | 19 ++---
>>   arch/powerpc/mm/nohash/kaslr_booke.c          | 71 +++++++++++++------
>>   7 files changed, 132 insertions(+), 36 deletions(-)
>>   rename Documentation/powerpc/{kaslr-booke32.rst => kaslr-booke.rst} (59%)
>>
>> -- 
>> 2.17.2
> 
> .
>