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. 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
