Re: [PATCH 4/6] ftrace, x86: make kernel text writable only forconversions

[Steven Rostedt]

On Thu, 19 Feb 2009, Andrew Morton wrote:

> On Thu, 19 Feb 2009 20:13:20 -0500
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> 
> > +int ftrace_arch_modify_prepare(void)
> > +{
> > +	/* at boot up, we are still writable */
> > +	if (system_state != SYSTEM_RUNNING)
> > +		return 0;
> > +
> > +	set_kernel_text_rw();
> > +	return 0;
> > +}
> > +
> > +int ftrace_arch_modify_post_process(void)
> > +{
> > +	/* at boot up, we are still writable */
> > +	if (system_state != SYSTEM_RUNNING)
> > +		return 0;
> > +
> > +	set_kernel_text_ro();
> > +	return 0;
> > +}
> 
> It would be prudent to avoid using system_state.  People can change the
> point at which it transitions and can unexpectedly insert (or move)
> code to sites where system_state has new values, etc.  It was a bad
> idea.

Good to know.

> 
> It would be clearer and more robust to create your own little flag for
> this purpose and set to it true and false at the places where that is
> appropriate for this application.  It's just one more byte...

I just did not want to set it to read-only before the main text decided to 
do this. I could probably move those checks into the set_kernel_text_* 
functions in init_32/64.c files. We should not convert until after the 
DEBUG_RODATA did its first conversion. Yeah, that's a better place for it.

I'll write up another patch.

Thanks,

-- Steve

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