linux-kernel - Re: [PATCH] livepatch: Prevent to enable uninitialized patch

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Date:	Tue, 12 May 2015 00:49:14 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Minfei Huang <minfei.huang@...mail.com>
cc:	Miroslav Benes <mbenes@...e.cz>, Minfei Huang <mhuang@...hat.com>,
	jpoimboe@...hat.com, sjenning@...hat.com,
	Vojtech Pavlik <vojtech@...e.cz>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] livepatch: Prevent to enable uninitialized patch

On Mon, 11 May 2015, Minfei Huang wrote:

> 1) Patched a patch to fix the issue for module A.
> 2) livepatch will try to enable the patch, while the corresponding
> module is loaded ( call klp_module_notify_coming )
> 3) Firstly, livepatch will do the instruction "obj->mod = mod", whatever
> the result of klp_module_notify_coming is.
> 4) livepatch may fail to call the klp_init_object_loaded or
> klp_enable_object
> 5) klp_module_notify_coming returns
> 
> 6) For the userspace, we can enable the patch again ( disable the patch
> firstly, then enable the patch from the sysfs )
> 7) In order to enable the patch, livepatch will call __klp_enable_patch
> 8) we can pass the limitation (klp_is_object_loaded), because the value
> of obj->mod is not NULL ( the obj->mod obtains the value from the step 3 )
> 9) the patch may be applied, although the patch is not initialized, if
> the value of func->old_addr is not NULL
> 
> From the above description, we can see the uninitialized patch ( the
> patch should be initialized by the klp_init_object_loaded in general )
> can be applied to the kernel.

This indeed looks like a valid breakage scenario.

Could you please resend v2 of this patch with much more detailed 
description in the changelog? (i.e. some reformulated variation on the 
text above). Your original submission didn't describe the problem your 
patch is fixing at all.

Thanks,

-- 
Jiri Kosina
SUSE Labs
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