[PATCH] powerpc/xmon: add read-only mode

[Christopher M Riedl]

> On March 29, 2019 at 3:41 AM Christophe Leroy <christophe.leroy at c-s.fr> wrote:
> 
> 
> 
> 
> Le 29/03/2019 à 05:21, cmr a écrit :
> > Operations which write to memory should be restricted on secure systems
> > and optionally to avoid self-destructive behaviors.
> > 
> > Add a config option, XMON_RO, to control default xmon behavior along
> > with kernel cmdline options xmon=ro and xmon=rw for explicit control.
> > The default is to enable read-only mode.
> > 
> > The following xmon operations are affected:
> > memops:
> > 	disable memmove
> > 	disable memset
> > memex:
> > 	no-op'd mwrite
> > super_regs:
> > 	no-op'd write_spr
> > bpt_cmds:
> > 	disable
> > proc_call:
> > 	disable
> > 
> > Signed-off-by: cmr <cmr at informatik.wtf>
> 
> A Fully qualified name should be used.

What do you mean by fully-qualified here? PPC_XMON_RO? (PPC_)XMON_READONLY?

> 
> > ---
> >   arch/powerpc/Kconfig.debug |  7 +++++++
> >   arch/powerpc/xmon/xmon.c   | 24 ++++++++++++++++++++++++
> >   2 files changed, 31 insertions(+)
> > 
> > diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
> > index 4e00cb0a5464..33cc01adf4cb 100644
> > --- a/arch/powerpc/Kconfig.debug
> > +++ b/arch/powerpc/Kconfig.debug
> > @@ -117,6 +117,13 @@ config XMON_DISASSEMBLY
> >   	  to say Y here, unless you're building for a memory-constrained
> >   	  system.
> >   
> > +config XMON_RO
> > +	bool "Set xmon read-only mode"
> > +	depends on XMON
> > +	default y
> 
> Should it really be always default y ?
> I would set default 'y' only when some security options are also set.
> 

This is a good point, I based this on an internal Slack suggestion but giving this more thought, disabling read-only mode by default makes more sense. I'm not sure what security options could be set though?