libbpf: Pass BPF token from find_prog_btf_id to BPF_BTF_GET_FD_BY_ID

Pass BPF token from bpf_program__set_attach_target to
BPF_BTF_GET_FD_BY_ID bpf command.
When freplace program attaches to target program, it needs to look up
for BTF of the target, this may require BPF token, if, for example,
running from user namespace.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20250317174039.161275-4-mykyta.yatsenko5@gmail.com

Author: mykyta5

tools/lib/bpf/bpf.c

@@ -1097,7 +1097,7 @@ int bpf_map_get_fd_by_id(__u32 id)
 int bpf_btf_get_fd_by_id_opts(__u32 id,
 			      const struct bpf_get_fd_by_id_opts *opts)
 {
-	const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
+	const size_t attr_sz = offsetofend(union bpf_attr, fd_by_id_token_fd);
 	union bpf_attr attr;
 	int fd;
 
@@ -1107,6 +1107,7 @@ int bpf_btf_get_fd_by_id_opts(__u32 id,
 	memset(&attr, 0, attr_sz);
 	attr.btf_id = id;
 	attr.open_flags = OPTS_GET(opts, open_flags, 0);
+	attr.fd_by_id_token_fd = OPTS_GET(opts, token_fd, 0);
 
 	fd = sys_bpf_fd(BPF_BTF_GET_FD_BY_ID, &attr, attr_sz);
 	return libbpf_err_errno(fd);

tools/lib/bpf/bpf.h

@@ -487,9 +487,10 @@ LIBBPF_API int bpf_link_get_next_id(__u32 start_id, __u32 *next_id);
 struct bpf_get_fd_by_id_opts {
 	size_t sz; /* size of this struct for forward/backward compatibility */
 	__u32 open_flags; /* permissions requested for the operation on fd */
+	__u32 token_fd;
 	size_t :0;
 };
-#define bpf_get_fd_by_id_opts__last_field open_flags
+#define bpf_get_fd_by_id_opts__last_field token_fd
 
 LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id);
 LIBBPF_API int bpf_prog_get_fd_by_id_opts(__u32 id,

tools/lib/bpf/btf.c

@@ -1619,12 +1619,18 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
 	return btf;
 }
 
-struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
+struct btf *btf_load_from_kernel(__u32 id, struct btf *base_btf, int token_fd)
 {
 	struct btf *btf;
 	int btf_fd;
+	LIBBPF_OPTS(bpf_get_fd_by_id_opts, opts);
+
+	if (token_fd) {
+		opts.open_flags |= BPF_F_TOKEN_FD;
+		opts.token_fd = token_fd;
+	}
 
-	btf_fd = bpf_btf_get_fd_by_id(id);
+	btf_fd = bpf_btf_get_fd_by_id_opts(id, &opts);
 	if (btf_fd < 0)
 		return libbpf_err_ptr(-errno);
 
@@ -1634,6 +1640,11 @@ struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
 	return libbpf_ptr(btf);
 }
 
+struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
+{
+	return btf_load_from_kernel(id, base_btf, 0);
+}
+
 struct btf *btf__load_from_kernel_by_id(__u32 id)
 {
 	return btf__load_from_kernel_by_id_split(id, NULL);

tools/lib/bpf/libbpf.c

@@ -10024,7 +10024,7 @@ int libbpf_find_vmlinux_btf_id(const char *name,
 	return libbpf_err(err);
 }
 
-static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
+static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd, int token_fd)
 {
 	struct bpf_prog_info info;
 	__u32 info_len = sizeof(info);
@@ -10044,7 +10044,7 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
 		pr_warn("The target program doesn't have BTF\n");
 		goto out;
 	}
-	btf = btf__load_from_kernel_by_id(info.btf_id);
+	btf = btf_load_from_kernel(info.btf_id, NULL, token_fd);
 	err = libbpf_get_error(btf);
 	if (err) {
 		pr_warn("Failed to get BTF %d of the program: %s\n", info.btf_id, errstr(err));
@@ -10127,7 +10127,7 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attac
 			pr_warn("prog '%s': attach program FD is not set\n", prog->name);
 			return -EINVAL;
 		}
-		err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd);
+		err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd, prog->obj->token_fd);
 		if (err < 0) {
 			pr_warn("prog '%s': failed to find BPF program (FD %d) BTF ID for '%s': %s\n",
 				prog->name, attach_prog_fd, attach_name, errstr(err));
@@ -12923,7 +12923,7 @@ struct bpf_link *bpf_program__attach_freplace(const struct bpf_program *prog,
 	if (target_fd) {
 		LIBBPF_OPTS(bpf_link_create_opts, target_opts);
 
-		btf_id = libbpf_find_prog_btf_id(attach_func_name, target_fd);
+		btf_id = libbpf_find_prog_btf_id(attach_func_name, target_fd, prog->obj->token_fd);
 		if (btf_id < 0)
 			return libbpf_err_ptr(btf_id);
 
@@ -13744,7 +13744,7 @@ int bpf_program__set_attach_target(struct bpf_program *prog,
 
 	if (attach_prog_fd) {
 		btf_id = libbpf_find_prog_btf_id(attach_func_name,
-						 attach_prog_fd);
+						 attach_prog_fd, prog->obj->token_fd);
 		if (btf_id < 0)
 			return libbpf_err(btf_id);
 	} else {

tools/lib/bpf/libbpf_internal.h

@@ -409,6 +409,7 @@ int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
 int btf_load_into_kernel(struct btf *btf,
 			 char *log_buf, size_t log_sz, __u32 log_level,
 			 int token_fd);
+struct btf *btf_load_from_kernel(__u32 id, struct btf *base_btf, int token_fd);
 
 struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf);
 void btf_get_kernel_prefix_kind(enum bpf_attach_type attach_type,