Subject: Re: [PATCH] powerpc:Don't print raw EIP/LR hex values in dump_stack() and show_regs()

From: Segher Boessenkool <[email-masked]>
Date: Mon, 21 Dec 2020 11:12:28 -0600

On Mon, Dec 21, 2020 at 04:42:23PM +0000, David Laight wrote:
> From: Segher Boessenkool
> > Sent: 21 December 2020 16:32
> > 
> > On Mon, Dec 21, 2020 at 04:17:21PM +0100, Christophe Leroy wrote:
> > > Le 21/12/2020 à 04:27, Xiaoming Ni a écrit :
> > > >Since the commit 2b0e86cc5de6 ("powerpc/fsl_booke/32: implement KASLR
> > > >infrastructure"), the powerpc system is ready to support KASLR.
> > > >To reduces the risk of invalidating address randomization, don't print the
> > > >EIP/LR hex values in dump_stack() and show_regs().
> > 
> > > I think your change is not enough to hide EIP address, see below a dump
> > > with you patch, you get "Faulting instruction address: 0xc03a0c14"
> > 
> > As far as I can see the patch does nothing to the GPR printout.  Often
> > GPRs contain code addresses.  As one example, the LR is moved via a GPR
> > (often GPR0, but not always) for storing on the stack.
> > 
> > So this needs more work.
> 
> If the dump_stack() is from an oops you need the real EIP value
> on order to stand any chance of making headway.

Or at least the function name + offset, yes.

> Otherwise you might just as well just print 'borked - tough luck'.

Yes.  ASLR is a house of cards.  But that isn't constructive wrt this
patch :-)

Segher