bpf: add verifier callback to get stack usage info for offloaded progs

In preparation for BPF-to-BPF calls in offloaded programs, add a new
function attribute to the struct bpf_prog_offload_ops so that drivers
supporting eBPF offload can hook at the end of program verification, and
potentially extract information collected by the verifier.

Implement a minimal callback (returning 0) in the drivers providing the
structs, namely netdevsim and nfp.

This will be useful in the nfp driver, in later commits, to extract the
number of subprograms as well as the stack depth for those subprograms.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

6 files changed, 37 insertions, 2 deletions

diff --git a/drivers/net/ethernet/netronome/nfp/bpf/verifier.c b/drivers/net/ethernet/netronome/nfp/bpf/verifier.c
index a6e9248669e1..e470489021e3 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/verifier.c
+++ b/drivers/net/ethernet/netronome/nfp/bpf/verifier.c
@@ -640,6 +640,12 @@ nfp_verify_insn(struct bpf_verifier_env *env, int insn_idx, int prev_insn_idx)
 	return 0;
 }
 
+static int nfp_bpf_finalize(struct bpf_verifier_env *env)
+{
+	return 0;
+}
+
 const struct bpf_prog_offload_ops nfp_bpf_analyzer_ops = {
-	.insn_hook = nfp_verify_insn,
+	.insn_hook	= nfp_verify_insn,
+	.finalize	= nfp_bpf_finalize,
 };
diff --git a/drivers/net/netdevsim/bpf.c b/drivers/net/netdevsim/bpf.c
index 81444208b216..cb3518474f0e 100644
--- a/drivers/net/netdevsim/bpf.c
+++ b/drivers/net/netdevsim/bpf.c
@@ -86,8 +86,14 @@ nsim_bpf_verify_insn(struct bpf_verifier_env *env, int insn_idx, int prev_insn)
 	return 0;
 }
 
+static int nsim_bpf_finalize(struct bpf_verifier_env *env)
+{
+	return 0;
+}
+
 static const struct bpf_prog_offload_ops nsim_bpf_analyzer_ops = {
-	.insn_hook = nsim_bpf_verify_insn,
+	.insn_hook	= nsim_bpf_verify_insn,
+	.finalize	= nsim_bpf_finalize,
 };
 
 static bool nsim_xdp_offload_active(struct netdevsim *ns)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 027697b6a22f..9b558713447f 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -263,6 +263,7 @@ struct bpf_verifier_ops {
 struct bpf_prog_offload_ops {
 	int (*insn_hook)(struct bpf_verifier_env *env,
 			 int insn_idx, int prev_insn_idx);
+	int (*finalize)(struct bpf_verifier_env *env);
 };
 
 struct bpf_prog_offload {
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7b6fd2ab3263..9e8056ec20fa 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -245,5 +245,6 @@ static inline struct bpf_reg_state *cur_regs(struct bpf_verifier_env *env)
 int bpf_prog_offload_verifier_prep(struct bpf_verifier_env *env);
 int bpf_prog_offload_verify_insn(struct bpf_verifier_env *env,
 				 int insn_idx, int prev_insn_idx);
+int bpf_prog_offload_finalize(struct bpf_verifier_env *env);
 
 #endif /* _LINUX_BPF_VERIFIER_H */
diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
index 177a52436394..8e93c47f0779 100644
--- a/kernel/bpf/offload.c
+++ b/kernel/bpf/offload.c
@@ -172,6 +172,24 @@ int bpf_prog_offload_verify_insn(struct bpf_verifier_env *env,
 	return ret;
 }
 
+int bpf_prog_offload_finalize(struct bpf_verifier_env *env)
+{
+	struct bpf_prog_offload *offload;
+	int ret = -ENODEV;
+
+	down_read(&bpf_devs_lock);
+	offload = env->prog->aux->offload;
+	if (offload) {
+		if (offload->dev_ops->finalize)
+			ret = offload->dev_ops->finalize(env);
+		else
+			ret = 0;
+	}
+	up_read(&bpf_devs_lock);
+
+	return ret;
+}
+
 static void __bpf_prog_offload_destroy(struct bpf_prog *prog)
 {
 	struct bpf_prog_offload *offload = prog->aux->offload;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 73c81bef6ae8..a0454cb299ba 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6309,6 +6309,9 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
 		env->cur_state = NULL;
 	}
 
+	if (ret == 0 && bpf_prog_is_dev_bound(env->prog->aux))
+		ret = bpf_prog_offload_finalize(env);
+
 skip_full_check:
 	while (!pop_stack(env, NULL, NULL));
 	free_states(env);