Re: [RFC PATCH 6/9] livepatch: create per-task consistency model

[Seth Jennings <sjenning@redhat.com>]

On Mon, Feb 09, 2015 at 11:31:18AM -0600, Josh Poimboeuf wrote:
> Add a basic per-task consistency model.  This is the foundation which
> will eventually enable us to patch those ~10% of security patches which
> change function prototypes and/or data semantics.
> 
> When a patch is enabled, livepatch enters into a transition state where
> tasks are converging from the old universe to the new universe.  If a
> given task isn't using any of the patched functions, it's switched to
> the new universe.  Once all the tasks have been converged to the new
> universe, patching is complete.
> 
> The same sequence occurs when a patch is disabled, except the tasks
> converge from the new universe to the old universe.
> 
> The /sys/kernel/livepatch/<patch>/transition file shows whether a patch
> is in transition.  Only a single patch (the topmost patch on the stack)
> can be in transition at a given time.  A patch can remain in the
> transition state indefinitely, if any of the tasks are stuck in the
> previous universe.
> 
> A transition can be reversed and effectively canceled by writing the
> opposite value to the /sys/kernel/livepatch/<patch>/enabled file while
> the transition is in progress.  Then all the tasks will attempt to
> converge back to the original universe.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
>  include/linux/livepatch.h     |  18 ++-
>  include/linux/sched.h         |   3 +
>  kernel/fork.c                 |   2 +
>  kernel/livepatch/Makefile     |   2 +-
>  kernel/livepatch/core.c       |  71 ++++++----
>  kernel/livepatch/patch.c      |  34 ++++-
>  kernel/livepatch/patch.h      |   1 +
>  kernel/livepatch/transition.c | 300 ++++++++++++++++++++++++++++++++++++++++++
>  kernel/livepatch/transition.h |  16 +++
>  kernel/sched/core.c           |   2 +
>  10 files changed, 423 insertions(+), 26 deletions(-)
>  create mode 100644 kernel/livepatch/transition.c
>  create mode 100644 kernel/livepatch/transition.h
> 
<snip>
> diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h
> new file mode 100644
> index 0000000..ba9a55c
> --- /dev/null
> +++ b/kernel/livepatch/transition.h
> @@ -0,0 +1,16 @@
> +#include <linux/livepatch.h>
> +
> +enum {
> +	KLP_UNIVERSE_UNDEFINED = -1,
> +	KLP_UNIVERSE_OLD,
> +	KLP_UNIVERSE_NEW,
> +};
> +
> +extern struct mutex klp_mutex;

klp_mutex isn't defined in transition.c.  Maybe this extern should be in
the transition.c file or in a core.h file, since core.c provides the
definition?

Thanks,
Seth

> +extern struct klp_patch *klp_transition_patch;
> +
> +extern void klp_init_transition(struct klp_patch *patch, int universe);
> +extern void klp_start_transition(int universe);
> +extern void klp_reverse_transition(void);
> +extern void klp_try_complete_transition(void);
> +extern void klp_complete_transition(void);
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 78d91e6..7b877f4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -74,6 +74,7 @@
>  #include <linux/binfmts.h>
>  #include <linux/context_tracking.h>
>  #include <linux/compiler.h>
> +#include <linux/livepatch.h>
>  
>  #include <asm/switch_to.h>
>  #include <asm/tlb.h>
> @@ -4601,6 +4602,7 @@ void init_idle(struct task_struct *idle, int cpu)
>  #if defined(CONFIG_SMP)
>  	sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
>  #endif
> +	klp_update_task_universe(idle);
>  }
>  
>  int cpuset_cpumask_can_shrink(const struct cpumask *cur,
> -- 
> 2.1.0
>