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

Jason Yan [off-list ref] writes:

Hi Daniel,

在 2020/2/26 15:16, Daniel Axtens 写道:

quoted

Hi Jason,

quoted

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.

quoted

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.

quoted

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

quoted

Regards,
Daniel

quoted

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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