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@suse.cz
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