linux-kernel - Re: [PATCH v2 1/2] livepatch: enforce patch stacking semantics

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Date:	Tue, 20 Jan 2015 16:33:28 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>, Vojtech Pavlik <vojtech@...e.cz>
CC:	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] livepatch: enforce patch stacking semantics

On 01/20/2015, 04:26 PM, Josh Poimboeuf wrote:
> Only allow the topmost patch on the stack to be enabled or disabled, so
> that patches can't be removed or added in an arbitrary order.
> 
> Suggested-by: Jiri Kosina <jkosina@...e.cz>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>

Reviewed-by: Jiri Slaby <jslaby@...e.cz>

> ---
>  kernel/livepatch/core.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 3d9c00b..2401e7f 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -379,6 +379,11 @@ static int __klp_disable_patch(struct klp_patch *patch)
>  	struct klp_object *obj;
>  	int ret;
>  
> +	/* enforce stacking: only the last enabled patch can be disabled */
> +	if (!list_is_last(&patch->list, &klp_patches) &&
> +	    list_next_entry(patch, list)->state == KLP_ENABLED)
> +		return -EBUSY;
> +
>  	pr_notice("disabling patch '%s'\n", patch->mod->name);
>  
>  	for (obj = patch->objs; obj->funcs; obj++) {
> @@ -435,6 +440,11 @@ static int __klp_enable_patch(struct klp_patch *patch)
>  	if (WARN_ON(patch->state != KLP_DISABLED))
>  		return -EINVAL;
>  
> +	/* enforce stacking: only the first disabled patch can be enabled */
> +	if (patch->list.prev != &klp_patches &&
> +	    list_prev_entry(patch, list)->state == KLP_DISABLED)
> +		return -EBUSY;
> +
>  	pr_notice_once("tainting kernel with TAINT_LIVEPATCH\n");
>  	add_taint(TAINT_LIVEPATCH, LOCKDEP_STILL_OK);
>  
> 

thanks,
-- 
js
suse labs
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