On Tue, 28 Jul 2026 20:59:58 -0400 Andrey Grodzovsky <[email protected]> wrote:
> kernel.ftrace_enabled=0 silently kills ftrace-based kprobes/kretprobes > the same way it does BPF trampolines: arm succeeds, the probe stops > firing with no error, and re-enabling silently restores it. Unlike > trampolines this is not a regression -- ftrace-based kprobes have > never carried this protection, so the bug is long-standing. > > kprobe_ftrace_ops/kprobe_ipmodify_ops are shared only among > ftrace-based kprobe attachers, not with any other tracer, so the same > unconditional FTRACE_OPS_FL_PERMANENT livepatch already uses applies > cleanly here too, with no kernel/trace/ftrace.c changes needed. > > Known limitation: kprobe.multi/kretprobe.multi/kprobe.session > (fprobe-backed, kernel/trace/fprobe.c) are not covered. Entry-only > fprobes could take the same fix, but return-capturing fprobes route > through the function-graph tracer's shared subops manager, which is > also used by unrelated tracers (function_graph, irqsoff, wakeup > latency, function profiler) -- marking it permanent would block > ftrace_enabled=0 for those too. Left for a follow-up. > In the another thread, Steve and you agreed to just remove ftrace_enabled, so I assume we will drop this patch. But from the kprobes point of view this seems reasonable change. Acked-by: Masami Hiramatsu (Google) <[email protected]> Thank you, > Cc: [email protected] > Assisted-by: Claude:claude-sonnet-5 > Signed-off-by: Andrey Grodzovsky <[email protected]> > --- > kernel/kprobes.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index bfc89083daa9..5a54511eee79 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -1122,14 +1122,15 @@ static struct kprobe *alloc_aggr_kprobe(struct kprobe > *p) > #endif /* CONFIG_OPTPROBES */ > > #ifdef CONFIG_KPROBES_ON_FTRACE > +/* Same protection livepatch gives its own ftrace_ops. */ > static struct ftrace_ops kprobe_ftrace_ops __read_mostly = { > .func = kprobe_ftrace_handler, > - .flags = FTRACE_OPS_FL_SAVE_REGS, > + .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_PERMANENT, > }; > > static struct ftrace_ops kprobe_ipmodify_ops __read_mostly = { > .func = kprobe_ftrace_handler, > - .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_IPMODIFY, > + .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_IPMODIFY | > FTRACE_OPS_FL_PERMANENT, > }; > > static int kprobe_ipmodify_enabled; > -- > 2.34.1 > -- Masami Hiramatsu (Google) <[email protected]>
