bpf: Make every prog keep a copy of ctx_arg_info

Currently, ctx_arg_info is read-only in the view of the verifier since
it is shared among programs of the same attach type. Make each program
have their own copy of ctx_arg_info so that we can use it to store
program specific information.

In the next patch where we support acquiring a referenced kptr through a
struct_ops argument tagged with "__ref", ctx_arg_info->ref_obj_id will
be used to store the unique reference object id of the argument. This
avoids creating a requirement in the verifier that "__ref" tagged
arguments must be the first set of references acquired [0].

[0] https://lore.kernel.org/bpf/20241220195619.2022866-2-amery.hung@gmail.com/

Signed-off-by: Amery Hung <ameryhung@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20250217190640.1748177-2-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 19 insertions, 17 deletions

diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 106735145948..380e9a7cac75 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -335,7 +335,7 @@ static void cache_btf_id(struct bpf_iter_target_info *tinfo,
 	tinfo->btf_id = prog->aux->attach_btf_id;
 }
 
-bool bpf_iter_prog_supported(struct bpf_prog *prog)
+int bpf_iter_prog_supported(struct bpf_prog *prog)
 {
 	const char *attach_fname = prog->aux->attach_func_name;
 	struct bpf_iter_target_info *tinfo = NULL, *iter;
@@ -344,7 +344,7 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)
 	int prefix_len = strlen(prefix);
 
 	if (strncmp(attach_fname, prefix, prefix_len))
-		return false;
+		return -EINVAL;
 
 	mutex_lock(&targets_mutex);
 	list_for_each_entry(iter, &targets, list) {
@@ -360,12 +360,11 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)
 	}
 	mutex_unlock(&targets_mutex);
 
-	if (tinfo) {
-		prog->aux->ctx_arg_info_size = tinfo->reg_info->ctx_arg_info_size;
-		prog->aux->ctx_arg_info = tinfo->reg_info->ctx_arg_info;
-	}
+	if (!tinfo)
+		return -EINVAL;
 
-	return tinfo != NULL;
+	return bpf_prog_ctx_arg_info_init(prog, tinfo->reg_info->ctx_arg_info,
+					  tinfo->reg_info->ctx_arg_info_size);
 }
 
 const struct bpf_func_proto *
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c420edbfb7c8..4b89a5df8ebc 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2313,6 +2313,7 @@ static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred)
 	kvfree(prog->aux->jited_linfo);
 	kvfree(prog->aux->linfo);
 	kfree(prog->aux->kfunc_tab);
+	kfree(prog->aux->ctx_arg_info);
 	if (prog->aux->attach_btf)
 		btf_put(prog->aux->attach_btf);
 
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3c286ec9e841..a231223d985b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -22405,6 +22405,15 @@ static void print_verification_stats(struct bpf_verifier_env *env)
 		env->peak_states, env->longest_mark_read_walk);
 }
 
+int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog,
+			       const struct bpf_ctx_arg_aux *info, u32 cnt)
+{
+	prog->aux->ctx_arg_info = kmemdup_array(info, cnt, sizeof(*info), GFP_KERNEL);
+	prog->aux->ctx_arg_info_size = cnt;
+
+	return prog->aux->ctx_arg_info ? 0 : -ENOMEM;
+}
+
 static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 {
 	const struct btf_type *t, *func_proto;
@@ -22485,17 +22494,12 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 		return -EACCES;
 	}
 
-	/* btf_ctx_access() used this to provide argument type info */
-	prog->aux->ctx_arg_info =
-		st_ops_desc->arg_info[member_idx].info;
-	prog->aux->ctx_arg_info_size =
-		st_ops_desc->arg_info[member_idx].cnt;
-
 	prog->aux->attach_func_proto = func_proto;
 	prog->aux->attach_func_name = mname;
 	env->ops = st_ops->verifier_ops;
 
-	return 0;
+	return bpf_prog_ctx_arg_info_init(prog, st_ops_desc->arg_info[member_idx].info,
+					  st_ops_desc->arg_info[member_idx].cnt);
 }
 #define SECURITY_PREFIX "security_"
 
@@ -22945,9 +22949,7 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 		prog->aux->attach_btf_trace = true;
 		return 0;
 	} else if (prog->expected_attach_type == BPF_TRACE_ITER) {
-		if (!bpf_iter_prog_supported(prog))
-			return -EINVAL;
-		return 0;
+		return bpf_iter_prog_supported(prog);
 	}
 
 	if (prog->type == BPF_PROG_TYPE_LSM) {