linux-kernel - Re: [PATCH 1/2] livepatch: Initialize shadow variables by init function safely

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Message-ID: <20180314202229.eck3aszdmwgsldyb@treble>
Date:   Wed, 14 Mar 2018 15:22:29 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     Petr Mladek <pmladek@...e.com>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>, Jessica Yu <jeyu@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] livepatch: Initialize shadow variables by init
 function safely

On Wed, Mar 14, 2018 at 03:43:01PM -0400, Joe Lawrence wrote:
> >> @@ -150,6 +145,23 @@ static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
> >>  		goto exists;
> >>  	}
> >>  
> >> +	new_shadow->obj = obj;
> >> +	new_shadow->id = id;
> >> +
> >> +	if (init_func) {
> >> +		int err;
> >> +
> >> +		err = init_func(obj, new_shadow->data, init_data);
> > 
> > Am I hallucinating, or will new_shadow->data always be NULL?  How did it
> > even work before?
> >
> struct klp_shadow {
>         struct hlist_node node;
>         struct rcu_head rcu_head;
>         void *obj;
>         unsigned long id;
>         char data[];            << not a pointer
> };

Ah.  This code needs a nice comment above the kzalloc() call, so I won't
get confused again next time.

-- 
Josh