linux-kernel - Re: [PATCH v5] livepatch: Prevent patch inconsistencies if the coming module notifier fails

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Message-ID: <alpine.LNX.2.00.1505181109370.8186@pobox.suse.cz>
Date:	Mon, 18 May 2015 11:09:51 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Minfei Huang <mhuang@...hat.com>
cc:	jpoimboe@...hat.com, sjenning@...hat.com, vojtech@...e.cz,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	Minfei Huang <mnfhuang@...il.com>
Subject: Re: [PATCH v5] livepatch: Prevent patch inconsistencies if the coming
 module notifier fails

On Fri, 15 May 2015, Minfei Huang wrote:

> From: Minfei Huang <mnfhuang@...il.com>
> 
> The previous patches can be applied, once the corresponding module is
> loaded. In general, the patch will do relocation (if necessary) and
> obtain/verify function address before we start to enable patch.
> 
> There are three different situations in which the coming module notifier
> can fail:
> 
> 1) relocations are not applied for some reason. In this case kallsyms
> for module symbol is not called at all. The patch is not applied to the
> module. If the user disable and enable patch again, there is possible
> bug in klp_enable_func. If the user specified func->old_addr for some
> function in the module (and he shouldn't do that, but nevertheless) our
> warning would not catch it, ftrace will reject to register the handler
> because of wrong address or will register the handler for wrong address.
> 
> 2) relocations are applied successfully, but kallsyms lookup fails. In
> this case func->old_addr can be correct for all previous lookups, 0 for
> current failed one, and "unspecified" for the rest. If we undergo the
> same scenario as in 1, the behaviour differs for three cases, but the
> patch is not enabled anyway.
> 
> 3) the object is initialized, but klp_enable_object fails in the
> notifier due to possible ftrace error. Since it is improbable that
> ftrace would heal itself in the future, we would get those errors
> everytime the patch is enabled.
> 
> In order to fix above situations, we can make obj->mod to NULL, if the
> coming modified notifier fails.
> 
> Signed-off-by: Minfei Huang <mnfhuang@...il.com>
> ---
> v4:
> - remove the label "out" in function klp_init_object_loaded
> v3:
> - modify the code style
> v2:
> - add the error message to make it more friendly
> - modify the commit log, base on the mbenes@...e.cz suggesting
> v1:
> - modify the commit log, describe the issue more details

Applied to for-4.2/upstream branch. Thanks,

-- 
Jiri Kosina
SUSE Labs
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