bpf: allow sleepable uprobe programs to attach

uprobe and kprobe programs have the same program type, KPROBE, which is
currently not allowed to load sleepable programs.

To avoid adding a new UPROBE type, we instead allow sleepable KPROBE
programs to load and defer the is-it-actually-a-uprobe-program check
to attachment time, where we're already validating the corresponding
perf_event.

A corollary of this patch is that you can now load a sleepable kprobe
program but cannot attach it.

Signed-off-by: Delyan Kratunov <delyank@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>

Author: Delyan Kratunov

kernel/bpf/verifier.c

@@ -14570,8 +14570,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 	}
 
 	if (prog->aux->sleepable && prog->type != BPF_PROG_TYPE_TRACING &&
-	    prog->type != BPF_PROG_TYPE_LSM) {
-		verbose(env, "Only fentry/fexit/fmod_ret and lsm programs can be sleepable\n");
+	    prog->type != BPF_PROG_TYPE_LSM && prog->type != BPF_PROG_TYPE_KPROBE) {
+		verbose(env, "Only fentry/fexit/fmod_ret, lsm, and kprobe/uprobe programs can be sleepable\n");
 		return -EINVAL;
 	}
 

kernel/events/core.c

@@ -10069,26 +10069,30 @@ static inline bool perf_event_is_tracing(struct perf_event *event)
 int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog,
 			    u64 bpf_cookie)
 {
-	bool is_kprobe, is_tracepoint, is_syscall_tp;
+	bool is_kprobe, is_uprobe, is_tracepoint, is_syscall_tp;
 
 	if (!perf_event_is_tracing(event))
 		return perf_event_set_bpf_handler(event, prog, bpf_cookie);
 
-	is_kprobe = event->tp_event->flags & TRACE_EVENT_FL_UKPROBE;
+	is_kprobe = event->tp_event->flags & TRACE_EVENT_FL_KPROBE;
+	is_uprobe = event->tp_event->flags & TRACE_EVENT_FL_UPROBE;
 	is_tracepoint = event->tp_event->flags & TRACE_EVENT_FL_TRACEPOINT;
 	is_syscall_tp = is_syscall_trace_event(event->tp_event);
-	if (!is_kprobe && !is_tracepoint && !is_syscall_tp)
+	if (!is_kprobe && !is_uprobe && !is_tracepoint && !is_syscall_tp)
 		/* bpf programs can only be attached to u/kprobe or tracepoint */
 		return -EINVAL;
 
-	if ((is_kprobe && prog->type != BPF_PROG_TYPE_KPROBE) ||
+	if (((is_kprobe || is_uprobe) && prog->type != BPF_PROG_TYPE_KPROBE) ||
 	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT) ||
 	    (is_syscall_tp && prog->type != BPF_PROG_TYPE_TRACEPOINT))
 		return -EINVAL;
 
+	if (prog->type == BPF_PROG_TYPE_KPROBE && prog->aux->sleepable && !is_uprobe)
+		/* only uprobe programs are allowed to be sleepable */
+		return -EINVAL;
+
 	/* Kprobe override only works for kprobes, not uprobes. */
-	if (prog->kprobe_override &&
-	    !(event->tp_event->flags & TRACE_EVENT_FL_KPROBE))
+	if (prog->kprobe_override && !is_kprobe)
 		return -EINVAL;
 
 	if (is_tracepoint || is_syscall_tp) {