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Message-ID: <87r1yhr2x1.fsf@dja-thinkpad.axtens.net>
Date: Wed, 26 Feb 2020 22:41:46 +1100
From: Daniel Axtens <dja@...ens.net>
To: Jason Yan <yanaijie@...wei.com>, 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, zhaohongjiang@...wei.com
Subject: Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64
Jason Yan <yanaijie@...wei.com> writes:
> 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.
I suspect that you will find it easier to convince people to accept a
change to %pK than removal :)
BTW, I have a T4240RDB so I might be able to test this series at some
point - do I need an updated bootloader to pass in a random seed, or is
the kernel able to get enough randomness by itself? (Sorry if this is
explained elsewhere in the series, I have only skimmed it lightly!)
Regards,
Daniel
>
> 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
>>
>> .
>>
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