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SubjectRe: [PATCH v2 2/5] livepatch: Basic API to track system state changes
On Fri, 19 Jul 2019, Petr Mladek wrote:

> This is another step how to help maintaining more livepatches.
>
> One big help was the atomic replace and cumulative livepatches. These
> livepatches replace the already installed ones. Therefore it should
> be enough when each cumulative livepatch is consistent.
>
> The problems might come with shadow variables and callbacks. They might
> change the system behavior or state so that it is no longer safe to
> go back and use an older livepatch or the original kernel code. Also
> any new livepatch must be able to detect what changes have already been
> done by the already installed livepatches.

"Also, a new livepatch must be able to detect changes which were made
by the already installed livepatches." would sound better to me.

> This is where the livepatch system state tracking gets useful. It
> allows to:
>
> - find whether a system state has already been modified by
> previous livepatches
>
> - store data needed to manipulate and restore the system state
>
> The information about the manipulated system states is stored in an
> array of struct klp_state. It can be searched by two new functions
> klp_get_state() and klp_get_prev_state().
>
> The dependencies are going to be solved by a version field added later.
> The only important information is that it will be allowed to modify
> the same state by more non-cumulative livepatches. It is the same logic
> as that it is allowed to modify the same function several times.

Wouldn't something like "It is similar to allowing to modify the same
function several times." be better to parse?

> The livepatch author is responsible for preventing incompatible
> changes.
>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> ---
> include/linux/livepatch.h | 15 +++++++++
> kernel/livepatch/Makefile | 2 +-
> kernel/livepatch/state.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 101 insertions(+), 1 deletion(-)
> create mode 100644 kernel/livepatch/state.c
>
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index 273400814020..9c8b637f17cd 100644
> --- a/include/linux/livepatch.h
> +++ b/include/linux/livepatch.h
> @@ -130,10 +130,21 @@ struct klp_object {
> bool patched;
> };
>
> +/**
> + * struct klp_state - state of the system modified by the livepatch
> + * @id: system state identifier (non zero)
> + * @data: custom data
> + */
> +struct klp_state {
> + unsigned long id;
> + void *data;
> +};
> +
> /**
> * struct klp_patch - patch structure for live patching
> * @mod: reference to the live patch module
> * @objs: object entries for kernel objects to be patched
> + * @states: system states that can get modified
> * @replace: replace all actively used patches
> * @list: list node for global list of actively used patches
> * @kobj: kobject for sysfs resources
> @@ -147,6 +158,7 @@ struct klp_patch {
> /* external */
> struct module *mod;
> struct klp_object *objs;
> + struct klp_state *states;
> bool replace;
>
> /* internal */
> @@ -217,6 +229,9 @@ void *klp_shadow_get_or_alloc(void *obj, unsigned long id,
> void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor);
> void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor);
>
> +struct klp_state *klp_get_state(struct klp_patch *patch, unsigned long id);
> +struct klp_state *klp_get_prev_state(unsigned long id);
> +
> #else /* !CONFIG_LIVEPATCH */
>
> static inline int klp_module_coming(struct module *mod) { return 0; }
> diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
> index cf9b5bcdb952..cf03d4bdfc66 100644
> --- a/kernel/livepatch/Makefile
> +++ b/kernel/livepatch/Makefile
> @@ -1,4 +1,4 @@
> # SPDX-License-Identifier: GPL-2.0-only
> obj-$(CONFIG_LIVEPATCH) += livepatch.o
>
> -livepatch-objs := core.o patch.o shadow.o transition.o
> +livepatch-objs := core.o patch.o shadow.o state.o transition.o
> diff --git a/kernel/livepatch/state.c b/kernel/livepatch/state.c
> new file mode 100644
> index 000000000000..f76d90e856b1
> --- /dev/null
> +++ b/kernel/livepatch/state.c
> @@ -0,0 +1,85 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * system_state.c - State of the system modified by livepatches
> + *
> + * Copyright (C) 2019 SUSE
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/livepatch.h>
> +#include "core.h"
> +#include "transition.h"
> +
> +#define klp_for_each_state(patch, state) \
> + for (state = patch->states; \
> + state && state->id; \
> + state++)
> +
> +/**
> + * klp_get_state() - get information about system state modified by
> + * the given patch
> + * @patch: livepatch that modifies the given system state
> + * @id: custom identifier of the modified system state
> + *
> + * Checks whether the given patch modifies to given system state.

s/to given/the given/ ?

Miroslav

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