linux-kernel - Re: [RFC PATCH v4 2/6] module: preserve Elf information for livepatch modules

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Message-ID: <alpine.LNX.2.00.1602091131510.22727@cbobk.fhfr.pm>
Date:	Tue, 9 Feb 2016 11:33:07 +0100 (CET)
From:	Jiri Kosina <jikos@...nel.org>
To:	Petr Mladek <pmladek@...e.com>
cc:	Jessica Yu <jeyu@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Miroslav Benes <mbenes@...e.cz>, linux-api@...r.kernel.org,
	live-patching@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH v4 2/6] module: preserve Elf information for livepatch
 modules

On Tue, 9 Feb 2016, Petr Mladek wrote:

> > +#ifdef CONFIG_KALLSYMS
> > +	/* Make symtab and strtab available prior to module init call */
> > +	mod->num_symtab = mod->core_num_syms;
> > +	mod->symtab = mod->core_symtab;
> > +	mod->strtab = mod->core_strtab;
> > +#endif
> 
> This should be done with module_mutex. Otherwise, it looks racy at least 
> against module_kallsyms_on_each_symbol().

Hmm, if this is the case, the comment describing the locking rules for 
module_mutex should be updated.

> BTW: I wonder why even the original code is not racy for example against 
> module_get_kallsym. It is called without the mutex. This code sets the 
> number of entries before the pointer to the entries.
> 
> Note that the module is in the list even in the UNFORMED state.

module_kallsyms_on_each_symbol() gives up in such case though.

-- 
Jiri Kosina
SUSE Labs