linux-kernel - Re: [PATCH 3/8] livepatch: Add atomic replace

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Date:   Mon, 9 Apr 2018 15:53:03 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     Petr Mladek <pmladek@...e.com>, Jiri Kosina <jikos@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] livepatch: Add atomic replace

> > +	 * see klp_init_object_loaded().
> > +	 */
> > +	if (!func->new_func && !func->nop)
> >  		return -EINVAL;
> 
> >  
> >  	INIT_LIST_HEAD(&func->stack_node);
> > @@ -742,6 +920,9 @@ static int klp_init_object_loaded(struct klp_patch *patch,
> >  			return -ENOENT;
> >  		}
> >  
> > +		if (func->nop)
> > +			func->new_func = (void *)func->old_addr;
> > +
> 
> These changes make it more obvious that 'new_func' isn't quite the right
> name.  It should really be 'new_addr' IMO.

I think we wanted to point out the difference from old_addr which is 
initialized with the symbol name while new_func is initialized with the 
new function itself (function pointer). I agree though that it looks 
awkward in this context and I'm not against changing it to new_addr.

Petr, could you also add a note to the changelog why we need to setup 
new_func for nop functions, please? It's not obvious because of the hack 
in klp_ftrace_handler() 
(klp_cancel_transition()->...->klp_check_stack_func() needs it).

Miroslav