Commit b5ea834d authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
Browse files

bpf: Support for new btf kind BTF_KIND_TAG 

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], [4]).
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
 [4] https://reviews.llvm.org/D109560



Signed-off-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210914223015.245546-1-yhs@fb.com
parent 41ced4cd

include/uapi/linux/btf.h

+13 −1
Original line number Diff line number Diff line
@@ -43,7 +43,7 @@ struct btf_type { 
	 * "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 {
@@ -74,6 +74,7 @@ enum { 
	BTF_KIND_VAR		= 14,	/* Variable	*/

	BTF_KIND_DATASEC	= 15,	/* Section	*/

	BTF_KIND_FLOAT		= 16,	/* Floating point	*/

	BTF_KIND_TAG		= 17,	/* Tag */



	NR_BTF_KINDS,

	BTF_KIND_MAX		= NR_BTF_KINDS - 1,
@@ -173,4 +174,15 @@ 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 applied location.

 * If component_idx == -1, the tag is applied to a struct, union,

 * variable or function. Otherwise, it is applied to a struct/union

 * member or a func argument, and component_idx indicates which member

 * or argument (0 ... vlen-1).

 */

struct btf_tag {

       __s32   component_idx;

};



#endif /* _UAPI__LINUX_BTF_H__ */

kernel/bpf/btf.c

+128 −0
Original line number Diff line number Diff line
@@ -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 +3820,110 @@ 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);

	s32 component_idx;

	const char *value;



	if (meta_left < meta_needed) {

		btf_verifier_log_basic(env, t,

				       "meta_left:%u meta_needed:%u",

				       meta_left, meta_needed);

		return -EINVAL;

	}



	value = btf_name_by_offset(env->btf, t->name_off);

	if (!value || !value[0]) {

		btf_verifier_log_type(env, t, "Invalid value");

		return -EINVAL;

	}



	if (btf_type_vlen(t)) {

		btf_verifier_log_type(env, t, "vlen != 0");

		return -EINVAL;

	}



	if (btf_type_kflag(t)) {

		btf_verifier_log_type(env, t, "Invalid btf_info kind_flag");

		return -EINVAL;

	}



	component_idx = btf_type_tag(t)->component_idx;

	if (component_idx < -1) {

		btf_verifier_log_type(env, t, "Invalid component_idx");

		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;

	s32 component_idx;

	u32 vlen;



	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);



	component_idx = btf_type_tag(t)->component_idx;

	if (component_idx != -1) {

		if (btf_type_is_var(next_type)) {

			btf_verifier_log_type(env, v->t, "Invalid component_idx");

			return -EINVAL;

		}



		if (btf_type_is_struct(next_type)) {

			vlen = btf_type_vlen(next_type);

		} else {

			/* next_type should be a function */

			next_type = btf_type_by_id(btf, next_type->type);

			vlen = btf_type_vlen(next_type);

		}



		if ((u32)component_idx >= vlen) {

			btf_verifier_log_type(env, v->t, "Invalid component_idx");

			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 component_idx=%d", t->type,

			 btf_type_tag(t)->component_idx);

}



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 +4058,7 @@ 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 +4143,10 @@ 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);

tools/include/uapi/linux/btf.h

+13 −1
Original line number Diff line number Diff line
@@ -43,7 +43,7 @@ struct btf_type { 
	 * "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 {
@@ -74,6 +74,7 @@ enum { 
	BTF_KIND_VAR		= 14,	/* Variable	*/

	BTF_KIND_DATASEC	= 15,	/* Section	*/

	BTF_KIND_FLOAT		= 16,	/* Floating point	*/

	BTF_KIND_TAG		= 17,	/* Tag */



	NR_BTF_KINDS,

	BTF_KIND_MAX		= NR_BTF_KINDS - 1,
@@ -173,4 +174,15 @@ 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 applied location.

 * If component_idx == -1, the tag is applied to a struct, union,

 * variable or function. Otherwise, it is applied to a struct/union

 * member or a func argument, and component_idx indicates which member

 * or argument (0 ... vlen-1).

 */

struct btf_tag {

       __s32   component_idx;

};



#endif /* _UAPI__LINUX_BTF_H__ */