bpf: Add bpf_btf_find_by_name_kind() helper.

Add new helper:
long bpf_btf_find_by_name_kind(char *name, int name_sz, u32 kind, int flags)
Description
	Find BTF type with given name and kind in vmlinux BTF or in module's BTFs.
Return
	Returns btf_id and btf_obj_fd in lower and upper 32 bits.

It will be used by loader program to find btf_id to attach the program to
and to find btf_ids of ksyms.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210514003623.28033-10-alexei.starovoitov@gmail.com

2 files changed, 64 insertions, 0 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index fbf6c06a9d62..85716327c375 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6085,3 +6085,65 @@ struct module *btf_try_get_module(const struct btf *btf)
 
 	return res;
 }
+
+BPF_CALL_4(bpf_btf_find_by_name_kind, char *, name, int, name_sz, u32, kind, int, flags)
+{
+	struct btf *btf;
+	long ret;
+
+	if (flags)
+		return -EINVAL;
+
+	if (name_sz <= 1 || name[name_sz - 1])
+		return -EINVAL;
+
+	btf = bpf_get_btf_vmlinux();
+	if (IS_ERR(btf))
+		return PTR_ERR(btf);
+
+	ret = btf_find_by_name_kind(btf, name, kind);
+	/* ret is never zero, since btf_find_by_name_kind returns
+	 * positive btf_id or negative error.
+	 */
+	if (ret < 0) {
+		struct btf *mod_btf;
+		int id;
+
+		/* If name is not found in vmlinux's BTF then search in module's BTFs */
+		spin_lock_bh(&btf_idr_lock);
+		idr_for_each_entry(&btf_idr, mod_btf, id) {
+			if (!btf_is_module(mod_btf))
+				continue;
+			/* linear search could be slow hence unlock/lock
+			 * the IDR to avoiding holding it for too long
+			 */
+			btf_get(mod_btf);
+			spin_unlock_bh(&btf_idr_lock);
+			ret = btf_find_by_name_kind(mod_btf, name, kind);
+			if (ret > 0) {
+				int btf_obj_fd;
+
+				btf_obj_fd = __btf_new_fd(mod_btf);
+				if (btf_obj_fd < 0) {
+					btf_put(mod_btf);
+					return btf_obj_fd;
+				}
+				return ret | (((u64)btf_obj_fd) << 32);
+			}
+			spin_lock_bh(&btf_idr_lock);
+			btf_put(mod_btf);
+		}
+		spin_unlock_bh(&btf_idr_lock);
+	}
+	return ret;
+}
+
+const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
+	.func		= bpf_btf_find_by_name_kind,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_MEM,
+	.arg2_type	= ARG_CONST_SIZE,
+	.arg3_type	= ARG_ANYTHING,
+	.arg4_type	= ARG_ANYTHING,
+};
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index da7dc2406470..f93ff2ebf96d 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4584,6 +4584,8 @@ syscall_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	switch (func_id) {
 	case BPF_FUNC_sys_bpf:
 		return &bpf_sys_bpf_proto;
+	case BPF_FUNC_btf_find_by_name_kind:
+		return &bpf_btf_find_by_name_kind_proto;
 	default:
 		return tracing_prog_func_proto(func_id, prog);
 	}