LLVM14 added support for a new C attribute ([1])
__attribute__((btf_tag("arbitrary_str")))
This attribute will be emitted to dwarf ([2]) and pahole
will convert it to BTF. Or for bpf target, this
attribute will be emitted to BTF directly ([3]).
The attribute is intended to provide additional
information for
- struct/union type or struct/union member
- static/global variables
- static/global function or function parameter.
For linux kernel, the btf_tag can be applied
in various places to specify user pointer,
function pre- or post- condition, function
allow/deny in certain context, etc. Such information
will be encoded in vmlinux BTF and can be used
by verifier.
The btf_tag can also be applied to bpf programs
to help global verifiable functions, e.g.,
specifying preconditions, etc.
This patch added basic parsing and checking support
in kernel for new BTF_KIND_TAG kind.
[1] https://reviews.llvm.org/D106614
[2] https://reviews.llvm.org/D106621
[3] https://reviews.llvm.org/D106622
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
include/uapi/linux/btf.h | 15 ++++-
kernel/bpf/btf.c | 115 +++++++++++++++++++++++++++++++++
tools/include/uapi/linux/btf.h | 15 ++++-
3 files changed, 139 insertions(+), 6 deletions(-)
diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
index d27b1708efe9..ca73c4449116 100644
--- a/include/uapi/linux/btf.h
+++ b/include/uapi/linux/btf.h
@@ -36,14 +36,14 @@ struct btf_type {
* bits 24-27: kind (e.g. int, ptr, array...etc)
* bits 28-30: unused
* bit 31: kind_flag, currently used by
- * struct, union and fwd
+ * struct, union, fwd and tag
*/
__u32 info;
/* "size" is used by INT, ENUM, STRUCT, UNION and DATASEC.
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
- * FUNC, FUNC_PROTO and VAR.
+ * FUNC, FUNC_PROTO, VAR and TAG.
* "type" is a type_id referring to another type.
*/
union {
@@ -73,7 +73,8 @@ struct btf_type {
#define BTF_KIND_VAR 14 /* Variable */
#define BTF_KIND_DATASEC 15 /* Section */
#define BTF_KIND_FLOAT 16 /* Floating point */
-#define BTF_KIND_MAX BTF_KIND_FLOAT
+#define BTF_KIND_TAG 17 /* Tag */
+#define BTF_KIND_MAX BTF_KIND_TAG
#define NR_BTF_KINDS (BTF_KIND_MAX + 1)
/* For some specific BTF_KIND, "struct btf_type" is immediately
@@ -170,4 +171,12 @@ struct btf_var_secinfo {
__u32 size;
};
+/* BTF_KIND_TAG is followed by a single "struct btf_tag" to describe
+ * additional information related to the tag such as which field of
+ * a struct or union or which argument of a function.
+ */
+struct btf_tag {
+ __u32 comp_id;
+};
+
#endif /* _UAPI__LINUX_BTF_H__ */
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index dfe61df4f974..9545290f804b 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -281,6 +281,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
[BTF_KIND_VAR] = "VAR",
[BTF_KIND_DATASEC] = "DATASEC",
[BTF_KIND_FLOAT] = "FLOAT",
+ [BTF_KIND_TAG] = "TAG",
};
const char *btf_type_str(const struct btf_type *t)
@@ -459,6 +460,17 @@ static bool btf_type_is_datasec(const struct btf_type *t)
return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
}
+static bool btf_type_is_tag(const struct btf_type *t)
+{
+ return BTF_INFO_KIND(t->info) == BTF_KIND_TAG;
+}
+
+static bool btf_type_is_tag_target(const struct btf_type *t)
+{
+ return btf_type_is_func(t) || btf_type_is_struct(t) ||
+ btf_type_is_var(t);
+}
+
u32 btf_nr_types(const struct btf *btf)
{
u32 total = 0;
@@ -537,6 +549,7 @@ const struct btf_type *btf_type_resolve_func_ptr(const struct btf *btf,
static bool btf_type_is_resolve_source_only(const struct btf_type *t)
{
return btf_type_is_var(t) ||
+ btf_type_is_tag(t) ||
btf_type_is_datasec(t);
}
@@ -563,6 +576,7 @@ static bool btf_type_needs_resolve(const struct btf_type *t)
btf_type_is_struct(t) ||
btf_type_is_array(t) ||
btf_type_is_var(t) ||
+ btf_type_is_tag(t) ||
btf_type_is_datasec(t);
}
@@ -616,6 +630,11 @@ static const struct btf_var *btf_type_var(const struct btf_type *t)
return (const struct btf_var *)(t + 1);
}
+static const struct btf_tag *btf_type_tag(const struct btf_type *t)
+{
+ return (const struct btf_tag *)(t + 1);
+}
+
static const struct btf_kind_operations *btf_type_ops(const struct btf_type *t)
{
return kind_ops[BTF_INFO_KIND(t->info)];
@@ -3801,6 +3820,97 @@ static const struct btf_kind_operations float_ops = {
.show = btf_df_show,
};
+static s32 btf_tag_check_meta(struct btf_verifier_env *env,
+ const struct btf_type *t,
+ u32 meta_left)
+{
+ const struct btf_tag *tag;
+ u32 meta_needed = sizeof(*tag);
+
+ if (meta_left < meta_needed) {
+ btf_verifier_log_basic(env, t,
+ "meta_left:%u meta_needed:%u",
+ meta_left, meta_needed);
+ return -EINVAL;
+ }
+
+ if (!t->name_off) {
+ btf_verifier_log_type(env, t, "Invalid name");
+ return -EINVAL;
+ }
+
+ if (btf_type_vlen(t)) {
+ btf_verifier_log_type(env, t, "vlen != 0");
+ return -EINVAL;
+ }
+
+ tag = btf_type_tag(t);
+ if (btf_type_kflag(t) && tag->comp_id) {
+ btf_verifier_log_type(env, t, "kflag/comp_id mismatch");
+ return -EINVAL;
+ }
+
+ btf_verifier_log_type(env, t, NULL);
+
+ return meta_needed;
+}
+
+static int btf_tag_resolve(struct btf_verifier_env *env,
+ const struct resolve_vertex *v)
+{
+ const struct btf_type *next_type;
+ const struct btf_type *t = v->t;
+ u32 next_type_id = t->type;
+ struct btf *btf = env->btf;
+ u32 vlen, comp_id;
+
+ next_type = btf_type_by_id(btf, next_type_id);
+ if (!next_type || !btf_type_is_tag_target(next_type)) {
+ btf_verifier_log_type(env, v->t, "Invalid type_id");
+ return -EINVAL;
+ }
+
+ if (!env_type_is_resolve_sink(env, next_type) &&
+ !env_type_is_resolved(env, next_type_id))
+ return env_stack_push(env, next_type, next_type_id);
+
+ if (!btf_type_kflag(t)) {
+ if (btf_type_is_struct(next_type)) {
+ vlen = btf_type_vlen(next_type);
+ } else if (btf_type_is_func(next_type)) {
+ next_type = btf_type_by_id(btf, next_type->type);
+ vlen = btf_type_vlen(next_type);
+ } else {
+ btf_verifier_log_type(env, v->t, "Invalid next_type");
+ return -EINVAL;
+ }
+
+ comp_id = btf_type_tag(t)->comp_id;
+ if (comp_id >= vlen) {
+ btf_verifier_log_type(env, v->t, "Invalid comp_id");
+ return -EINVAL;
+ }
+ }
+
+ env_stack_pop_resolved(env, next_type_id, 0);
+
+ return 0;
+}
+
+static void btf_tag_log(struct btf_verifier_env *env, const struct btf_type *t)
+{
+ btf_verifier_log(env, "type=%u", t->type);
+}
+
+static const struct btf_kind_operations tag_ops = {
+ .check_meta = btf_tag_check_meta,
+ .resolve = btf_tag_resolve,
+ .check_member = btf_df_check_member,
+ .check_kflag_member = btf_df_check_kflag_member,
+ .log_details = btf_tag_log,
+ .show = btf_df_show,
+};
+
static int btf_func_proto_check(struct btf_verifier_env *env,
const struct btf_type *t)
{
@@ -3935,6 +4045,7 @@ static const struct btf_kind_operations * const kind_ops[NR_BTF_KINDS] = {
[BTF_KIND_VAR] = &var_ops,
[BTF_KIND_DATASEC] = &datasec_ops,
[BTF_KIND_FLOAT] = &float_ops,
+ [BTF_KIND_TAG] = &tag_ops,
};
static s32 btf_check_meta(struct btf_verifier_env *env,
@@ -4019,6 +4130,10 @@ static bool btf_resolve_valid(struct btf_verifier_env *env,
return !btf_resolved_type_id(btf, type_id) &&
!btf_resolved_type_size(btf, type_id);
+ if (btf_type_is_tag(t))
+ return btf_resolved_type_id(btf, type_id) &&
+ !btf_resolved_type_size(btf, type_id);
+
if (btf_type_is_modifier(t) || btf_type_is_ptr(t) ||
btf_type_is_var(t)) {
t = btf_type_id_resolve(btf, &type_id);
diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
index d27b1708efe9..ca73c4449116 100644
--- a/tools/include/uapi/linux/btf.h
+++ b/tools/include/uapi/linux/btf.h
@@ -36,14 +36,14 @@ struct btf_type {
* bits 24-27: kind (e.g. int, ptr, array...etc)
* bits 28-30: unused
* bit 31: kind_flag, currently used by
- * struct, union and fwd
+ * struct, union, fwd and tag
*/
__u32 info;
/* "size" is used by INT, ENUM, STRUCT, UNION and DATASEC.
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
- * FUNC, FUNC_PROTO and VAR.
+ * FUNC, FUNC_PROTO, VAR and TAG.
* "type" is a type_id referring to another type.
*/
union {
@@ -73,7 +73,8 @@ struct btf_type {
#define BTF_KIND_VAR 14 /* Variable */
#define BTF_KIND_DATASEC 15 /* Section */
#define BTF_KIND_FLOAT 16 /* Floating point */
-#define BTF_KIND_MAX BTF_KIND_FLOAT
+#define BTF_KIND_TAG 17 /* Tag */
+#define BTF_KIND_MAX BTF_KIND_TAG
#define NR_BTF_KINDS (BTF_KIND_MAX + 1)
/* For some specific BTF_KIND, "struct btf_type" is immediately
@@ -170,4 +171,12 @@ struct btf_var_secinfo {
__u32 size;
};
+/* BTF_KIND_TAG is followed by a single "struct btf_tag" to describe
+ * additional information related to the tag such as which field of
+ * a struct or union or which argument of a function.
+ */
+struct btf_tag {
+ __u32 comp_id;
+};
+
#endif /* _UAPI__LINUX_BTF_H__ */
--
2.30.2
