[PATCH bpf v4 3/7] netdevsim: Add debugfs toggle to reject BPF programs in verifier

["Toke Høiland-Jørgensen" <toke@redhat.com>]

From: Toke Høiland-Jørgensen <toke@redhat.com>

This adds a new debugfs toggle ('bpf_bind_verifier_accept') that can be
used to make netdevsim reject BPF programs from being accepted by the
verifier. If this toggle (which defaults to true) is set to false,
nsim_bpf_verify_insn() will return EOPNOTSUPP on the last
instruction (after outputting the 'Hello from netdevsim' verifier message).

This makes it possible to check the verification callback in the driver
from test_offload.py in selftests, since the verifier now clears the
verifier log on a successful load, hiding the message from the driver.

Fixes: 6f8a57ccf851 ("bpf: Make verifier log more relevant by default")
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 drivers/net/netdevsim/bpf.c       |   12 ++++++++++--
 drivers/net/netdevsim/netdevsim.h |    1 +
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/net/netdevsim/bpf.c b/drivers/net/netdevsim/bpf.c
index 85546664bdd5..90aafb56f140 100644
--- a/drivers/net/netdevsim/bpf.c
+++ b/drivers/net/netdevsim/bpf.c
@@ -63,15 +63,20 @@ static int
 nsim_bpf_verify_insn(struct bpf_verifier_env *env, int insn_idx, int prev_insn)
 {
 	struct nsim_bpf_bound_prog *state;
+	int ret = 0;
 
 	state = env->prog->aux->offload->dev_priv;
 	if (state->nsim_dev->bpf_bind_verifier_delay && !insn_idx)
 		msleep(state->nsim_dev->bpf_bind_verifier_delay);
 
-	if (insn_idx == env->prog->len - 1)
+	if (insn_idx == env->prog->len - 1) {
 		pr_vlog(env, "Hello from netdevsim!\n");
 
-	return 0;
+		if (!state->nsim_dev->bpf_bind_verifier_accept)
+			ret = -EOPNOTSUPP;
+	}
+
+	return ret;
 }
 
 static int nsim_bpf_finalize(struct bpf_verifier_env *env)
@@ -595,6 +600,9 @@ int nsim_bpf_dev_init(struct nsim_dev *nsim_dev)
 			    &nsim_dev->bpf_bind_accept);
 	debugfs_create_u32("bpf_bind_verifier_delay", 0600, nsim_dev->ddir,
 			   &nsim_dev->bpf_bind_verifier_delay);
+	nsim_dev->bpf_bind_verifier_accept = true;
+	debugfs_create_bool("bpf_bind_verifier_accept", 0600, nsim_dev->ddir,
+			    &nsim_dev->bpf_bind_verifier_accept);
 	return 0;
 }
 
diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
index 827fc80f50a0..c4e7ad2a1964 100644
--- a/drivers/net/netdevsim/netdevsim.h
+++ b/drivers/net/netdevsim/netdevsim.h
@@ -189,6 +189,7 @@ struct nsim_dev {
 	struct dentry *take_snapshot;
 	struct bpf_offload_dev *bpf_dev;
 	bool bpf_bind_accept;
+	bool bpf_bind_verifier_accept;
 	u32 bpf_bind_verifier_delay;
 	struct dentry *ddir_bpf_bound_progs;
 	u32 prog_id_gen;