Re: [PATCHv3 bpf-next 1/2] bpf: Do not allow to load sleepable BPF_TRACE_RAW_TP program

[Jiri Olsa <olsajiri@xxxxxxxxx>]

On Mon, Jan 16, 2023 at 11:17:56PM -0800, Yonghong Song wrote:
> 
> 
> On 1/16/23 5:29 AM, Jiri Olsa wrote:
> > Currently we allow to load any tracing program as sleepable,
> > but BPF_TRACE_RAW_TP can't sleep. Making the check explicit
> > for tracing programs attach types, so sleepable BPF_TRACE_RAW_TP
> > will fail to load.
> > 
> > Updating the verifier error to mention iter programs as well.
> > 
> > Acked-by: Song Liu <song@xxxxxxxxxx>
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> 
> Ack with a minor comment below.
> 
> Acked-by: Yonghong Song <yhs@xxxxxx>
> 
> > ---
> > v3 changes:
> >    - use switch in can_be_sleepable [Alexei]
> >    - added acks [Song]
> > 
> >   kernel/bpf/verifier.c | 22 +++++++++++++++++++---
> >   1 file changed, 19 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index fa4c911603e9..966dbfc14288 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -16743,6 +16743,23 @@ BTF_ID(func, rcu_read_unlock_strict)
> >   #endif
> >   BTF_SET_END(btf_id_deny)
> > +static bool can_be_sleepable(struct bpf_prog *prog)
> > +{
> > +	if (prog->type == BPF_PROG_TYPE_TRACING) {
> > +		switch (prog->expected_attach_type) {
> > +		case BPF_TRACE_FENTRY:
> > +		case BPF_TRACE_FEXIT:
> > +		case BPF_MODIFY_RETURN:
> > +		case BPF_TRACE_ITER:
> > +			return true;
> > +		default:
> > +			return false;
> > +		}
> > +	}
> > +	return prog->type == BPF_PROG_TYPE_LSM ||
> > +	       prog->type == BPF_PROG_TYPE_KPROBE;
> > +}
> > +
> >   static int check_attach_btf_id(struct bpf_verifier_env *env)
> >   {
> >   	struct bpf_prog *prog = env->prog;
> > @@ -16761,9 +16778,8 @@ 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");
> > +	if (prog->aux->sleepable && !can_be_sleepable(prog)) {
> > +		verbose(env, "Only fentry/fexit/fmod_ret, lsm, iter and kprobe/uprobe programs can be sleepable\n");
> 
> actually kprobe programs cannot be sleepable. See kernel/events/core.c.
> perf_event_set_bpf_prog(...)
> ...
> 
>         if (prog->type == BPF_PROG_TYPE_KPROBE && prog->aux->sleepable &&
> !is_uprobe)
>                 /* only uprobe programs are allowed to be sleepable */
>                 return -EINVAL;
> 
> So I suggest to add a comment and remove the above 'kprobe' from error
> message.

ok, is comment below ok?

jirka


---
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fa4c911603e9..ca7db2ce70b9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -16743,6 +16743,23 @@ BTF_ID(func, rcu_read_unlock_strict)
 #endif
 BTF_SET_END(btf_id_deny)
 
+static bool can_be_sleepable(struct bpf_prog *prog)
+{
+	if (prog->type == BPF_PROG_TYPE_TRACING) {
+		switch (prog->expected_attach_type) {
+		case BPF_TRACE_FENTRY:
+		case BPF_TRACE_FEXIT:
+		case BPF_MODIFY_RETURN:
+		case BPF_TRACE_ITER:
+			return true;
+		default:
+			return false;
+		}
+	}
+	return prog->type == BPF_PROG_TYPE_LSM ||
+	       prog->type == BPF_PROG_TYPE_KPROBE; /* only for uprobes */
+}
+
 static int check_attach_btf_id(struct bpf_verifier_env *env)
 {
 	struct bpf_prog *prog = env->prog;
@@ -16761,9 +16778,8 @@ 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");
+	if (prog->aux->sleepable && !can_be_sleepable(prog)) {
+		verbose(env, "Only fentry/fexit/fmod_ret, lsm, iter and uprobe programs can be sleepable\n");
 		return -EINVAL;
 	}