linux-kernel - Re: [PATCH] module: exclude SHN_UNDEF symbols from kallsyms api

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Message-ID: <20180605135701.hfoxr5tkz7svmwkn@treble>
Date:   Tue, 5 Jun 2018 08:57:01 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     linux-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: [PATCH] module: exclude SHN_UNDEF symbols from kallsyms api

On Tue, Jun 05, 2018 at 10:42:23AM +0200, Jessica Yu wrote:
> Livepatch modules are special in that we preserve their entire symbol
> tables in order to be able to apply relocations after module load. The
> unwanted side effect of this is that undefined (SHN_UNDEF) symbols of
> livepatch modules are accessible via the kallsyms api and this can
> confuse symbol resolution in livepatch (klp_find_object_symbol()) and
> cause subtle bugs in livepatch.
> 
> Have the module kallsyms api skip over SHN_UNDEF symbols. These symbols
> are usually not available for normal modules anyway as we cut down their
> symbol tables to just the core (non-undefined) symbols, so this should
> really just affect livepatch modules. Note that this patch doesn't
> affect the display of undefined symbols in /proc/kallsyms.
> 
> Reported-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Tested-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Jessica Yu <jeyu@...nel.org>

Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh