linux-kernel - /proc/kallsyms shows undefined symbols for livepatch modules

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Date:   Sat, 2 Jun 2018 12:32:33 -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: /proc/kallsyms shows undefined symbols for livepatch modules

Hi Jessica,

I found a bug:

  [root@f25 ~]# modprobe livepatch-sample
  [root@f25 ~]# grep ' u ' /proc/kallsyms
  ffffffff81161080 u klp_enable_patch	[livepatch_sample]
  ffffffff81a01800 u __fentry__	[livepatch_sample]
  ffffffff81161250 u klp_unregister_patch	[livepatch_sample]
  ffffffff81161870 u klp_register_patch	[livepatch_sample]
  ffffffff8131f0b0 u seq_printf	[livepatch_sample]

Notice that livepatch modules' undefined symbols are showing up in
/proc/kallsyms.  This can confuse klp_find_object_symbol() which can
cause subtle bugs in livepatch.

I stared at the module kallsyms code for a bit, but I don't see the bug.
Maybe it has something to do with how we save the symbol table in
copy_module_elf().  Any ideas?

-- 
Josh