libbpf: Support exclusive map creation

Implement setters and getters that allow map to be registered as
exclusive to the specified program. The registration should be done
before the exclusive program is loaded.

Signed-off-by: KP Singh <kpsingh@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20250914215141.15144-5-kpsingh@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 69 insertions, 0 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a39640bd5448..5161c2b39875 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -499,6 +499,7 @@ struct bpf_program {
 	__u32 line_info_rec_size;
 	__u32 line_info_cnt;
 	__u32 prog_flags;
+	__u8  hash[SHA256_DIGEST_LENGTH];
 };
 
 struct bpf_struct_ops {
@@ -578,6 +579,7 @@ struct bpf_map {
 	bool autocreate;
 	bool autoattach;
 	__u64 map_extra;
+	struct bpf_program *excl_prog;
 };
 
 enum extern_type {
@@ -4488,6 +4490,44 @@ bpf_object__section_to_libbpf_map_type(const struct bpf_object *obj, int shndx)
 	}
 }
 
+static int bpf_prog_compute_hash(struct bpf_program *prog)
+{
+	struct bpf_insn *purged;
+	int i, err;
+
+	purged = calloc(prog->insns_cnt, BPF_INSN_SZ);
+	if (!purged)
+		return -ENOMEM;
+
+	/* If relocations have been done, the map_fd needs to be
+	 * discarded for the digest calculation.
+	 */
+	for (i = 0; i < prog->insns_cnt; i++) {
+		purged[i] = prog->insns[i];
+		if (purged[i].code == (BPF_LD | BPF_IMM | BPF_DW) &&
+		    (purged[i].src_reg == BPF_PSEUDO_MAP_FD ||
+		     purged[i].src_reg == BPF_PSEUDO_MAP_VALUE)) {
+			purged[i].imm = 0;
+			i++;
+			if (i >= prog->insns_cnt ||
+			    prog->insns[i].code != 0 ||
+			    prog->insns[i].dst_reg != 0 ||
+			    prog->insns[i].src_reg != 0 ||
+			    prog->insns[i].off != 0) {
+				err = -EINVAL;
+				goto out;
+			}
+			purged[i] = prog->insns[i];
+			purged[i].imm = 0;
+		}
+	}
+	err = libbpf_sha256(purged, prog->insns_cnt * sizeof(struct bpf_insn),
+			    prog->hash, SHA256_DIGEST_LENGTH);
+out:
+	free(purged);
+	return err;
+}
+
 static int bpf_program__record_reloc(struct bpf_program *prog,
 				     struct reloc_desc *reloc_desc,
 				     __u32 insn_idx, const char *sym_name,
@@ -5237,6 +5277,14 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
 	create_attr.token_fd = obj->token_fd;
 	if (obj->token_fd)
 		create_attr.map_flags |= BPF_F_TOKEN_FD;
+	if (map->excl_prog) {
+		err = bpf_prog_compute_hash(map->excl_prog);
+		if (err)
+			return err;
+
+		create_attr.excl_prog_hash = map->excl_prog->hash;
+		create_attr.excl_prog_hash_size = SHA256_DIGEST_LENGTH;
+	}
 
 	if (bpf_map__is_struct_ops(map)) {
 		create_attr.btf_vmlinux_value_type_id = map->btf_vmlinux_value_type_id;
@@ -10527,6 +10575,27 @@ int bpf_map__set_inner_map_fd(struct bpf_map *map, int fd)
 	return 0;
 }
 
+int bpf_map__set_exclusive_program(struct bpf_map *map, struct bpf_program *prog)
+{
+	if (map_is_created(map)) {
+		pr_warn("exclusive programs must be set before map creation\n");
+		return libbpf_err(-EINVAL);
+	}
+
+	if (map->obj != prog->obj) {
+		pr_warn("excl_prog and map must be from the same bpf object\n");
+		return libbpf_err(-EINVAL);
+	}
+
+	map->excl_prog = prog;
+	return 0;
+}
+
+struct bpf_program *bpf_map__exclusive_program(struct bpf_map *map)
+{
+	return map->excl_prog;
+}
+
 static struct bpf_map *
 __bpf_map__iter(const struct bpf_map *m, const struct bpf_object *obj, int i)
 {