[RFC bpf-next v2 4/9] bpf: use attached BTF to find correct type info of struct_ops progs.

[thinker.li@gmail.com]

From: Kui-Feng Lee <thinker.li@gmail.com>

The signatures may be declared in the module defining the structs type.
So, we need to know which module BTF to look for type information.  The
later patches will make libbpf to attach module BTFs to programs. This
patch tries to use the attached BTF if there is.
---
 include/uapi/linux/bpf.h       |  4 ++++
 kernel/bpf/bpf_struct_ops.c    | 11 ++++++++++-
 kernel/bpf/syscall.c           |  2 +-
 kernel/bpf/verifier.c          |  4 +++-
 tools/include/uapi/linux/bpf.h |  4 ++++
 5 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8790b3962e4b..f0882d341433 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1383,6 +1383,10 @@ union bpf_attr {
 		 * to using 5 hash functions).
 		 */
 		__u64	map_extra;
+
+		__u32   mod_btf_fd;	/* fd pointing to a BTF type data
+					 * for btf_vmlinux_value_type_id.
+					 */
 	};
 
 	struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 82cc3f0638fa..c93baf54a538 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -786,7 +786,16 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	struct bpf_map *map;
 	struct btf *btf;
 
-	st_ops = bpf_struct_ops_find_value(attr->btf_vmlinux_value_type_id, btf_vmlinux);
+	/* XXX: We need a module name or ID to find a BTF type. */
+	/* XXX: should use btf from attr->btf_fd */
+	if (attr->mod_btf_fd) {
+		btf = btf_get_by_fd(attr->mod_btf_fd);
+		if (IS_ERR(btf))
+			return ERR_PTR(PTR_ERR(btf));
+	} else {
+		btf = btf_vmlinux;
+	}
+	st_ops = bpf_struct_ops_find_value(attr->btf_vmlinux_value_type_id, btf);
 	if (!st_ops)
 		return ERR_PTR(-ENOTSUPP);
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index eb01c31ed591..04d3017b7db1 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1093,7 +1093,7 @@ static int map_check_btf(struct bpf_map *map, const struct btf *btf,
 	return ret;
 }
 
-#define BPF_MAP_CREATE_LAST_FIELD map_extra
+#define BPF_MAP_CREATE_LAST_FIELD mod_btf_fd
 /* called via syscall */
 static int map_create(union bpf_attr *attr)
 {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c0cab601b2a6..8eab8d3fc398 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19183,6 +19183,7 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 	const struct btf_member *member;
 	struct bpf_prog *prog = env->prog;
 	u32 btf_id, member_idx;
+	struct btf *btf;
 	const char *mname;
 
 	if (!prog->gpl_compatible) {
@@ -19190,8 +19191,9 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 		return -EINVAL;
 	}
 
+	btf = prog->aux->attach_btf;
 	btf_id = prog->aux->attach_btf_id;
-	st_ops = bpf_struct_ops_find(btf_id, btf_vmlinux);
+	st_ops = bpf_struct_ops_find(btf_id, btf);
 	if (!st_ops) {
 		verbose(env, "attach_btf_id %u is not a supported struct\n",
 			btf_id);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 8790b3962e4b..f0882d341433 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1383,6 +1383,10 @@ union bpf_attr {
 		 * to using 5 hash functions).
 		 */
 		__u64	map_extra;
+
+		__u32   mod_btf_fd;	/* fd pointing to a BTF type data
+					 * for btf_vmlinux_value_type_id.
+					 */
 	};
 
 	struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
-- 
2.34.1