[RFC bpf-next v3 08/11] bpf: pass attached BTF to find correct type info of struct_ops progs.

[thinker.li@gmail.com]

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

The type info of a struct_ops type may be in a module.  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 passes attached BTF
from syscall to bpf_struct_ops subsystem to make sure attached BTF is
available when the bpf_struct_ops subsystem is ready to use it.

bpf_prog has attach_btf in aux from attach_btf_obj_fd, that is pass along
with the bpf_attr loading the program. attach_btf is used to find the btf
type of attach_btf_id. attach_btf_id is used to identify the traced
function for a trace program.  For struct_ops programs, it is used to
identify the struct_ops type of the struct_ops object a program attached
to.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
 include/uapi/linux/bpf.h       |  4 ++++
 kernel/bpf/bpf_struct_ops.c    | 12 +++++++++++-
 kernel/bpf/syscall.c           |  2 +-
 kernel/bpf/verifier.c          |  4 +++-
 tools/include/uapi/linux/bpf.h |  4 ++++
 5 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 73b155e52204..178d6fa45fa0 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1390,6 +1390,10 @@ 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 8b5c859377e9..d5600d9ad302 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -765,9 +765,19 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
 	struct bpf_struct_ops_map *st_map;
 	const struct btf_type *t, *vt;
 	struct bpf_map *map;
+	struct btf *btf;
 	int ret;
 
-	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 85c1d908f70f..fed3870fec7a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1097,7 +1097,7 @@ 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 99b45501951c..11f85dbc911b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19623,6 +19623,7 @@ 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) {
@@ -19630,8 +19631,9 @@ 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 73b155e52204..178d6fa45fa0 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1390,6 +1390,10 @@ 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