[External] Re: Question - Livepatch/Kprobe Coexistence on Ftrace-enabled Functions (Ubuntu kernel based on Linux stable 5.15.30)

[Song Liu]

On Mon, Oct 20, 2025 at 7:56 AM Andrey Grodzovsky
<andrey.grodzovsky at crowdstrike.com> wrote:
[...]
> > If you build the kernel from source code, there are some samples in
> > samples/livepatch that you can use for testing. PS: You need to enable
> >
> >    CONFIG_SAMPLE_LIVEPATCH=m
> >
> > I hope this helps.
>
> Thanks Song, working on repro, kernel rebuilt, test module is loading
> but, bpftrace is refusing to attach now to fentries/fexits claiming the
> costum kernel is not supporting it. It did
> attach in the case of stock AWS kernel i copied the .config from. So
> just trying to figure out now if some Kcofnig flags are missing or
> different . Let me know in case you manage to confirm yourself in the
> meanwhile the fix works for
> you.

Yes, it worked in my tests.

[root@(none) /]# kpatch load linux/samples/livepatch/livepatch-sample.ko
loading patch module: linux/samples/livepatch/livepatch-sample.ko
[root@(none) /]# bpftrace.real -e 'fexit:cmdline_proc_show
{printf("fexit\n");}' &
[1] 388
[root@(none) /]# Attached 1 probe
[root@(none) /]# bpftrace.real -e 'fentry:cmdline_proc_show
{printf("fentry\n");}' &
[2] 397
[root@(none) /]# Attached 1 probe

[root@(none) /]# cat /proc/cmdline
this has been live patched
fentry
fexit

Thanks,
Song