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

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Date:	Fri, 15 May 2015 10:15:56 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Minfei Huang <mhuang@...hat.com>
Cc:	sjenning@...hat.com, jkosina@...e.cz, 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, May 15, 2015 at 10:22:48AM +0800, 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>

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

Thanks!

-- 
Josh
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