linux-kernel - Re: [PATCH v3] livepatch: add (un)patch callbacks

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Date:   Wed, 16 Aug 2017 15:29:23 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jessica Yu <jeyu@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Chris J Arges <chris.j.arges@...onical.com>
Subject: Re: [PATCH v3] livepatch: add (un)patch callbacks

On Wed, Aug 16, 2017 at 03:17:04PM -0400, Joe Lawrence wrote:
> Provide livepatch modules a klp_object (un)patching notification
> mechanism.  Pre and post-(un)patch callbacks allow livepatch modules to
> setup or synchronize changes that would be difficult to support in only
> patched-or-unpatched code contexts.
> 
> Callbacks can be registered for target module or vmlinux klp_objects,
> but each implementation is klp_object specific.
> 
>   - Pre-(un)patch callbacks run before any (un)patching action takes
>     place.
> 
>   - Post-(un)patch callbacks run once an object has been (un)patched and
>     the klp_patch fully transitioned to its target state.
> 
> Example use cases include modification of global data and registration
> of newly available services/handlers.
> 
> See Documentation/livepatch/callback.txt for details.
> 
> Signed-off-by: Joe Lawrence <joe.lawrence@...hat.com>
> ---
>  Documentation/livepatch/callbacks.txt        |  87 ++++++++++++
>  include/linux/livepatch.h                    |  81 ++++++++++++
>  kernel/livepatch/core.c                      |  37 ++++--
>  kernel/livepatch/patch.c                     |   5 +-
>  kernel/livepatch/transition.c                |  21 ++-
>  samples/livepatch/Makefile                   |   2 +
>  samples/livepatch/livepatch-callbacks-demo.c | 190 +++++++++++++++++++++++++++
>  samples/livepatch/livepatch-callbacks-mod.c  |  53 ++++++++
>  8 files changed, 462 insertions(+), 14 deletions(-)
>  create mode 100644 Documentation/livepatch/callbacks.txt
>  create mode 100644 samples/livepatch/livepatch-callbacks-demo.c
>  create mode 100644 samples/livepatch/livepatch-callbacks-mod.c
> 
> diff --git a/Documentation/livepatch/callbacks.txt b/Documentation/livepatch/callbacks.txt
> new file mode 100644
> index 000000000000..e18f2678f3bb
> --- /dev/null
> +++ b/Documentation/livepatch/callbacks.txt
> @@ -0,0 +1,87 @@
> +(Un)patching Callbacks
> +======================
> +
> +Livepatch (un)patch-callbacks provide a mechanism for livepatch modules
> +to execute callback functions when a kernel object is (un)patched.  They
> +can be considered a "power feature" that extends livepatching abilities
> +to include:
> +
> +  - Safe updates to global data
> +
> +  - "Patches" to init and probe functions
> +
> +  - Patching otherwise unpatchable code (i.e. assembly)
> +
> +In most cases, (un)patch hooks will need to be used in conjunction with

s/hooks/callbacks/

(though I wouldn't be opposed to changing them back to "hooks" anyway as
it's one fewer syllable :-) but no strong opinion either way on that)

-- 
Josh