On Mon 2021-11-22 10:53:21, Joe Lawrence wrote: > On 11/22/21 2:57 AM, Miroslav Benes wrote: > > On Fri, 19 Nov 2021, Josh Poimboeuf wrote: > > > >> Thanks for doing this! And at peterz-esque speed no less :-) > >> > >> On Fri, Nov 19, 2021 at 10:03:26AM +0100, Miroslav Benes wrote: > >>> livepatch's consistency model requires that no live patched function > >>> must be found on any task's stack during a transition process after a > >>> live patch is applied. It is achieved by walking through stacks of all > >>> blocked tasks. > >>> > >>> The user might also want to define more functions to search for without > >>> them being patched at all. It may either help with preparing a live > >>> patch, which would otherwise require additional touches to achieve the > >>> consistency > >> > >> Do we have any examples of this situation we can add to the commit log? > > > > I do not have anything at hand. Joe, do you remember the case you > > mentioned previously about adding a nop to a function? > > Maybe adding a hypothetical scenario to the commit log would suffice? I wonder if we could describe a scenario based on the thread about .cold code variants, see https://lore.kernel.org/all/20211112015003.pefl656m3zmir6ov@treble/ This feature would allow to safely livepatch already released kernels where the unwinder is not able to reliably detect a newly discovered problems. > >>> or it can be used to overcome deficiencies the stack > >>> checking inherently has. For example, GCC may optimize a function so > >>> that a part of it is moved to a different section and the function would > >>> jump to it. This child function would not be found on a stack in this > >>> case, but it may be important to search for it so that, again, the > >>> consistency is achieved. > >>> > >>> Allow the user to specify such functions on klp_object level. > >>> > >>> Signed-off-by: Miroslav Benes <mbenes@xxxxxxx> > >>> --- > >>> include/linux/livepatch.h | 11 +++++++++++ > >>> kernel/livepatch/core.c | 16 ++++++++++++++++ > >>> kernel/livepatch/transition.c | 21 ++++++++++++++++----- > >>> 3 files changed, 43 insertions(+), 5 deletions(-) > >>> > >>> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h > >>> index 2614247a9781..89df578af8c3 100644 > >>> --- a/include/linux/livepatch.h > >>> +++ b/include/linux/livepatch.h > >>> @@ -106,9 +106,11 @@ struct klp_callbacks { > >>> * struct klp_object - kernel object structure for live patching > >>> * @name: module name (or NULL for vmlinux) > >>> * @funcs: function entries for functions to be patched in the object > >>> + * @funcs_stack: function entries for functions to be stack checked > >> > >> So there are two arrays/lists of 'klp_func', and two implied meanings of > >> what a 'klp_func' is and how it's initialized. > >> > >> Might it be simpler and more explicit to just add a new external field > >> to 'klp_func' and continue to have a single 'funcs' array? Similar to > >> what we already do with the special-casing of 'nop', except it would be > >> an external field, e.g. 'no_patch' or 'stack_only'. > > I'll add that the first thing that came to mind when you raised this > feature idea in the other thread was to support existing klp_funcs array > with NULL new_func's. Please, solve this with the extra flag, e.g. .stack_only, as already suggested. It will help to distinguish mistakes and intentions. Also it will allow to find these symbols by grep. > I didn't go look to see how invasive it would be, > but it will be interesting to see if a single list approach turns out > any simpler for v2. I am not sure either. But I expect that it will be easier than the extra array. Best Regards, Petr
