linux-kernel - Re: [PATCH v8 7/8] livepatch: Correctly handle atomic replace for not yet loaded modules

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Date:   Thu, 1 Mar 2018 11:28:59 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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 v8 7/8] livepatch: Correctly handle atomic replace for
 not yet loaded modules

On Thu 2018-02-22 22:00:28, Miroslav Benes wrote:
> On Wed, 21 Feb 2018, Petr Mladek wrote:
> > This patch allows the late initialization.
> > 
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index ad508a86b2f9..da1438d47d83 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> > @@ -984,7 +988,12 @@ static void klp_free_patch(struct klp_patch *patch)
> >  
> >  static int klp_init_func(struct klp_object *obj, struct klp_func *func)
> >  {
> > -	if (!func->old_name || !func->new_func)
> > +	if (!func->old_name)
> > +		return -EINVAL;
> > +
> > +	/* NOPs do not know the address until the patched module is loaded. */
> > +	if (!func->new_func &&
> > +	    (!klp_is_func_type(func, KLP_FUNC_NOP) || klp_is_object_loaded(obj)))
> >  		return -EINVAL;
> 
> If we changed the order of klp_init_func() and klp_init_object_loaded() 
> calls in klp_init_object(), the hunk would not be needed. Is that correct? 

Not really. klp_init_object_loaded() would set func->new_func only
when the object was loaded. But we want to proceed here and create
the kobject for NOPs even when it was not loaded.


> >  	INIT_LIST_HEAD(&func->stack_node);
> > @@ -1039,6 +1048,9 @@ static int klp_init_object_loaded(struct klp_patch *patch,
> >  			return -ENOENT;
> >  		}
> >  
> > +		if (klp_is_func_type(func, KLP_FUNC_NOP))
> > +			func->new_func = (void *)func->old_addr;
> 
> Is there a reason why you left the same assignment in 
> klp_alloc_func_nop()? This one is enough, no?

Good point! I am going to replace the obsolete assignment
with a comment in v8.

Best Regards,
Petr