Commit 8c42d2fa authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
Browse files

bpf: Support BTF_KIND_TYPE_TAG for btf_type_tag attributes 

LLVM patches ([1] for clang, [2] and [3] for BPF backend)
added support for btf_type_tag attributes. This patch
added support for the kernel.

The main motivation for btf_type_tag is to bring kernel
annotations __user, __rcu etc. to btf. With such information
available in btf, bpf verifier can detect mis-usages
and reject the program. For example, for __user tagged pointer,
developers can then use proper helper like bpf_probe_read_user()
etc. to read the data.

BTF_KIND_TYPE_TAG may also useful for other tracing
facility where instead of to require user to specify
kernel/user address type, the kernel can detect it
by itself with btf.

  [1] https://reviews.llvm.org/D111199
  [2] https://reviews.llvm.org/D113222
  [3] https://reviews.llvm.org/D113496



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/20211112012609.1505032-1-yhs@fb.com
parent 2326ff8d

include/uapi/linux/btf.h

+2 −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, VAR and DECL_TAG.

	 * FUNC, FUNC_PROTO, VAR, DECL_TAG and TYPE_TAG.

	 * "type" is a type_id referring to another type.

	 */

	union {
@@ -75,6 +75,7 @@ enum { 
	BTF_KIND_DATASEC	= 15,	/* Section	*/

	BTF_KIND_FLOAT		= 16,	/* Floating point	*/

	BTF_KIND_DECL_TAG	= 17,	/* Decl Tag */

	BTF_KIND_TYPE_TAG	= 18,	/* Type Tag */



	NR_BTF_KINDS,

	BTF_KIND_MAX		= NR_BTF_KINDS - 1,

kernel/bpf/btf.c

+13 −1
Original line number Diff line number Diff line
@@ -282,6 +282,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = { 
	[BTF_KIND_DATASEC]	= "DATASEC",

	[BTF_KIND_FLOAT]	= "FLOAT",

	[BTF_KIND_DECL_TAG]	= "DECL_TAG",

	[BTF_KIND_TYPE_TAG]	= "TYPE_TAG",

};



const char *btf_type_str(const struct btf_type *t)
@@ -418,6 +419,7 @@ static bool btf_type_is_modifier(const struct btf_type *t) 
	case BTF_KIND_VOLATILE:

	case BTF_KIND_CONST:

	case BTF_KIND_RESTRICT:

	case BTF_KIND_TYPE_TAG:

		return true;

	}
@@ -1737,6 +1739,7 @@ __btf_resolve_size(const struct btf *btf, const struct btf_type *type, 
		case BTF_KIND_VOLATILE:

		case BTF_KIND_CONST:

		case BTF_KIND_RESTRICT:

		case BTF_KIND_TYPE_TAG:

			id = type->type;

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

			break;
@@ -2345,6 +2348,8 @@ static int btf_ref_type_check_meta(struct btf_verifier_env *env, 
				   const struct btf_type *t,

				   u32 meta_left)

{

	const char *value;



	if (btf_type_vlen(t)) {

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

		return -EINVAL;
@@ -2360,7 +2365,7 @@ static int btf_ref_type_check_meta(struct btf_verifier_env *env, 
		return -EINVAL;

	}



	/* typedef type must have a valid name, and other ref types,

	/* typedef/type_tag type must have a valid name, and other ref types,

	 * volatile, const, restrict, should have a null name.

	 */

	if (BTF_INFO_KIND(t->info) == BTF_KIND_TYPEDEF) {
@@ -2369,6 +2374,12 @@ static int btf_ref_type_check_meta(struct btf_verifier_env *env, 
			btf_verifier_log_type(env, t, "Invalid name");

			return -EINVAL;

		}

	} else if (BTF_INFO_KIND(t->info) == BTF_KIND_TYPE_TAG) {

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

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

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

			return -EINVAL;

		}

	} else {

		if (t->name_off) {

			btf_verifier_log_type(env, t, "Invalid name");
@@ -4059,6 +4070,7 @@ static const struct btf_kind_operations * const kind_ops[NR_BTF_KINDS] = { 
	[BTF_KIND_DATASEC] = &datasec_ops,

	[BTF_KIND_FLOAT] = &float_ops,

	[BTF_KIND_DECL_TAG] = &decl_tag_ops,

	[BTF_KIND_TYPE_TAG] = &modifier_ops,

};



static s32 btf_check_meta(struct btf_verifier_env *env,

tools/include/uapi/linux/btf.h

+2 −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, VAR and DECL_TAG.

	 * FUNC, FUNC_PROTO, VAR, DECL_TAG and TYPE_TAG.

	 * "type" is a type_id referring to another type.

	 */

	union {
@@ -75,6 +75,7 @@ enum { 
	BTF_KIND_DATASEC	= 15,	/* Section	*/

	BTF_KIND_FLOAT		= 16,	/* Floating point	*/

	BTF_KIND_DECL_TAG	= 17,	/* Decl Tag */

	BTF_KIND_TYPE_TAG	= 18,	/* Type Tag */



	NR_BTF_KINDS,

	BTF_KIND_MAX		= NR_BTF_KINDS - 1,