Subject: Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble memory as ROX

From: Mike Rapoport <[email-masked]>
Date: Thu, 1 Jun 2023 14:07:13 +0300

On Thu, Jun 01, 2023 at 12:30:50PM +0200, Peter Zijlstra wrote:
> On Thu, Jun 01, 2023 at 01:12:56PM +0300, Mike Rapoport wrote:
> 
> > +static void __init_or_module do_text_poke(void *addr, const void *opcode, size_t len)
> > +{
> > +	if (system_state < SYSTEM_RUNNING) {
> > +		text_poke_early(addr, opcode, len);
> > +	} else {
> > +		mutex_lock(&text_mutex);
> > +		text_poke(addr, opcode, len);
> > +		mutex_unlock(&text_mutex);
> > +	}
> > +}
> 
> So I don't much like do_text_poke(); why?

I believe the idea was to keep memcpy for early boot before the kernel
image is protected without going and adding if (is_module_text_address())
all over the place.

I think this can be used instead without updating all the call sites of
text_poke_early():

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 91057de8e6bc..f994e63e9903 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1458,7 +1458,7 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
 		 * code cannot be running and speculative code-fetches are
 		 * prevented. Just change the code.
 		 */
-		memcpy(addr, opcode, len);
+		text_poke_copy(addr, opcode, len);
 	} else {
 		local_irq_save(flags);
 		memcpy(addr, opcode, len);
 
> > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> > index aa99536b824c..d50595f2c1a6 100644
> > --- a/arch/x86/kernel/ftrace.c
> > +++ b/arch/x86/kernel/ftrace.c
> > @@ -118,10 +118,13 @@ ftrace_modify_code_direct(unsigned long ip, const char *old_code,
> >  		return ret;
> >  
> >  	/* replace the text with the new text */
> > -	if (ftrace_poke_late)
> > +	if (ftrace_poke_late) {
> >  		text_poke_queue((void *)ip, new_code, MCOUNT_INSN_SIZE, NULL);
> > -	else
> > -		text_poke_early((void *)ip, new_code, MCOUNT_INSN_SIZE);
> > +	} else {
> > +		mutex_lock(&text_mutex);
> > +		text_poke((void *)ip, new_code, MCOUNT_INSN_SIZE);
> > +		mutex_unlock(&text_mutex);
> > +	}
> >  	return 0;
> >  }
> 
> And in the above case it's actively wrong for loosing the _queue()
> thing.

-- 
Sincerely yours,
Mike.