Re: bpf_probe_read_user EFAULT

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Jan 04, 2023 at 11:08:23PM +0100, Jiri Olsa wrote:
> On Wed, Jan 04, 2023 at 10:42:02PM +0100, Jiri Olsa wrote:
> > On Wed, Jan 04, 2023 at 04:24:27PM +0100, Victor Laforet wrote:
> > > Ok thanks. As I understand, tp_btf/+ probes (specifically tp_btf/sched_switch that I need) cannot be sleepable? It is then not possible to read user space memory from the bpf code?
> > 
> > yes, only fentry/fexit/fmod_ret, lsm, and kprobe/uprobe programs can be sleepable

we actually allow to create tp_btf program with BPF_F_SLEEPABLE flag,
because it's TRACING prog type, but still bpf program can't sleep when
executed in tracepoint context..  so I wonder we should not allow to
load it, Alexei?

jirka


---
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 98a8051ce316..390621d79fbb 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -16755,10 +16755,14 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 		return -EINVAL;
 	}
 
-	if (prog->aux->sleepable && prog->type != BPF_PROG_TYPE_TRACING &&
-	    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;
+	if (prog->aux->sleepable) {
+		if ((prog->type == BPF_PROG_TYPE_TRACING &&
+		     prog->expected_attach_type == BPF_TRACE_RAW_TP) ||
+		    (prog->type != BPF_PROG_TYPE_TRACING &&
+		     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;
+		}
 	}
 
 	if (prog->type == BPF_PROG_TYPE_STRUCT_OPS)