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

[Jason Yan]

å 2020/3/5 5:21, Scott Wood åé:
> On Wed, 2020-02-26 at 18:16 +1100, Daniel Axtens wrote:
> > 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?
> > 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.
> >
> > Maybe replacing the REG format string in KASLR mode would be sufficient?
>
> Whatever we decide to do here, it's not book3e-specific so it should be
> considered separately from these patches.

OK, I will continue to work with this series.

> -Scott
>
>
>
> .