[PATCH v2] powerpc: Avoid code patching freed init sections

[Michael Neuling]

> > --- a/arch/powerpc/lib/code-patching.c
> > +++ b/arch/powerpc/lib/code-patching.c
> > @@ -23,11 +23,33 @@
> >   #include <asm/code-patching.h>
> >   #include <asm/setup.h>
> >   
> > +
> 
> This blank line is not needed

Ack

> 
> > +static inline bool in_init_section(unsigned int *patch_addr)
> > +{
> > +	if (patch_addr < (unsigned int *)__init_begin)
> > +		return false;
> > +	if (patch_addr >= (unsigned int *)__init_end)
> > +		return false;
> > +	return true;
> > +}
> 
> Can we use the existing function init_section_contains() instead of this 
> new function ?

Nice, I was looking for something like that... 

> > +
> > +static inline bool init_freed(void)
> > +{
> > +	return (system_state >= SYSTEM_RUNNING);
> > +}
> > +
> 
> I would call this function differently, for instance init_is_finished(), 
> because as you mentionned it doesn't exactly mean that init memory is freed.

Talking to Nick and mpe offline I think we are going to have to add a flag when
we free init mem rather than doing what we have now since what we have now has a
potential race. That change will eliminate the function entirely.

> >   static int __patch_instruction(unsigned int *exec_addr, unsigned int
> > instr,
> >   			       unsigned int *patch_addr)
> >   {
> >   	int err;
> >   
> > +	/* Make sure we aren't patching a freed init section */
> > +	if (in_init_section(patch_addr) && init_freed()) {
> 
> The test must be done on exec_addr, not on patch_addr, as patch_addr is 
> the address where the instruction as been remapped RW for allowing its 
> modification.

Thanks for the catch

> Also I think it should be tested the other way round, because the 
> init_freed() is a simpler test which will be false most of the time once 
> the system is running so it should be checked first.

ok, I'll change.

> > +		printk(KERN_DEBUG "Skipping init section patching addr:
> > 0x%lx\n",
> 
> Maybe use pr_debug() instead.

Sure.

> 
> > +			(unsigned long)patch_addr);
> 
> Please align second line as per Codying style.

Sorry I can't see what's wrong. You're (or Cody :-P) going to have to spell it
this out for me...

> 
> > +		return 0;
> > +	}
> > +
> >   	__put_user_size(instr, patch_addr, 4, err);
> >   	if (err)
> >   		return err;
> > 
> 
> I think it would be better to put this verification in 
> patch_instruction() instead, to avoid RW mapping/unmapping the 
> instruction to patch when we are not going to do the patching.

If we do it there then we miss the raw_patch_intruction case.

IMHO I don't think we need to optimise this rare and non-critical path. 

Mikey