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Commit 69b693f0 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Daniel Borkmann
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bpf: btf: Introduce BPF Type Format (BTF) 



This patch introduces BPF type Format (BTF).

BTF (BPF Type Format) is the meta data format which describes
the data types of BPF program/map.  Hence, it basically focus
on the C programming language which the modern BPF is primary
using.  The first use case is to provide a generic pretty print
capability for a BPF map.

BTF has its root from CTF (Compact C-Type format).  To simplify
the handling of BTF data, BTF removes the differences between
small and big type/struct-member.  Hence, BTF consistently uses u32
instead of supporting both "one u16" and "two u32 (+padding)" in
describing type and struct-member.

It also raises the number of types (and functions) limit
from 0x7fff to 0x7fffffff.

Due to the above changes,  the format is not compatible to CTF.
Hence, BTF starts with a new BTF_MAGIC and version number.

This patch does the first verification pass to the BTF.  The first
pass checks:
1. meta-data size (e.g. It does not go beyond the total btf's size)
2. name_offset is valid
3. Each BTF_KIND (e.g. int, enum, struct....) does its
   own check of its meta-data.

Some other checks, like checking a struct's member is referring
to a valid type, can only be done in the second pass.  The second
verification pass will be implemented in the next patch.

Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 97e19cce

include/uapi/linux/btf.h

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/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */

/* Copyright (c) 2018 Facebook */

#ifndef _UAPI__LINUX_BTF_H__

#define _UAPI__LINUX_BTF_H__



#include <linux/types.h>



#define BTF_MAGIC	0xeB9F

#define BTF_MAGIC_SWAP	0x9FeB

#define BTF_VERSION	1

#define BTF_FLAGS_COMPR	0x01



struct btf_header {

	__u16	magic;

	__u8	version;

	__u8	flags;



	__u32	parent_label;

	__u32	parent_name;



	/* All offsets are in bytes relative to the end of this header */

	__u32	label_off;	/* offset of label section	*/

	__u32	object_off;	/* offset of data object section*/

	__u32	func_off;	/* offset of function section	*/

	__u32	type_off;	/* offset of type section	*/

	__u32	str_off;	/* offset of string section	*/

	__u32	str_len;	/* length of string section	*/

};



/* Max # of type identifier */

#define BTF_MAX_TYPE	0x7fffffff

/* Max offset into the string section */

#define BTF_MAX_NAME_OFFSET	0x7fffffff

/* Max # of struct/union/enum members or func args */

#define BTF_MAX_VLEN	0xffff



/* The type id is referring to a parent BTF */

#define BTF_TYPE_PARENT(id)	(((id) >> 31) & 0x1)

#define BTF_TYPE_ID(id)		((id) & BTF_MAX_TYPE)



/* String is in the ELF string section */

#define BTF_STR_TBL_ELF_ID(ref)	(((ref) >> 31) & 0x1)

#define BTF_STR_OFFSET(ref)	((ref) & BTF_MAX_NAME_OFFSET)



struct btf_type {

	__u32 name;

	/* "info" bits arrangement

	 * bits  0-15: vlen (e.g. # of struct's members)

	 * bits 16-23: unused

	 * bits 24-28: kind (e.g. int, ptr, array...etc)

	 * bits 29-30: unused

	 * bits    31: root

	 */

	__u32 info;

	/* "size" is used by INT, ENUM, STRUCT and UNION.

	 * "size" tells the size of the type it is describing.

	 *

	 * "type" is used by PTR, TYPEDEF, VOLATILE, CONST and RESTRICT.

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

	 */

	union {

		__u32 size;

		__u32 type;

	};

};



#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x1f)

#define BTF_INFO_ISROOT(info)	(!!(((info) >> 24) & 0x80))

#define BTF_INFO_VLEN(info)	((info) & 0xffff)



#define BTF_KIND_UNKN		0	/* Unknown	*/

#define BTF_KIND_INT		1	/* Integer	*/

#define BTF_KIND_PTR		2	/* Pointer	*/

#define BTF_KIND_ARRAY		3	/* Array	*/

#define BTF_KIND_STRUCT		4	/* Struct	*/

#define BTF_KIND_UNION		5	/* Union	*/

#define BTF_KIND_ENUM		6	/* Enumeration	*/

#define BTF_KIND_FWD		7	/* Forward	*/

#define BTF_KIND_TYPEDEF	8	/* Typedef	*/

#define BTF_KIND_VOLATILE	9	/* Volatile	*/

#define BTF_KIND_CONST		10	/* Const	*/

#define BTF_KIND_RESTRICT	11	/* Restrict	*/

#define BTF_KIND_MAX		11

#define NR_BTF_KINDS		12



/* For some specific BTF_KIND, "struct btf_type" is immediately

 * followed by extra data.

 */



/* BTF_KIND_INT is followed by a u32 and the following

 * is the 32 bits arrangement:

 */

#define BTF_INT_ENCODING(VAL)	(((VAL) & 0xff000000) >> 24)

#define BTF_INT_OFFSET(VAL)	(((VAL  & 0x00ff0000)) >> 16)

#define BTF_INT_BITS(VAL)	((VAL)  & 0x0000ffff)



/* Attributes stored in the BTF_INT_ENCODING */

#define BTF_INT_SIGNED	0x1

#define BTF_INT_CHAR	0x2

#define BTF_INT_BOOL	0x4

#define BTF_INT_VARARGS	0x8



/* BTF_KIND_ENUM is followed by multiple "struct btf_enum".

 * The exact number of btf_enum is stored in the vlen (of the

 * info in "struct btf_type").

 */

struct btf_enum {

	__u32	name;

	__s32	val;

};



/* BTF_KIND_ARRAY is followed by one "struct btf_array" */

struct btf_array {

	__u32	type;

	__u32	index_type;

	__u32	nelems;

};



/* BTF_KIND_STRUCT and BTF_KIND_UNION are followed

 * by multiple "struct btf_member".  The exact number

 * of btf_member is stored in the vlen (of the info in

 * "struct btf_type").

 */

struct btf_member {

	__u32	name;

	__u32	type;

	__u32	offset;	/* offset in bits */

};



#endif /* _UAPI__LINUX_BTF_H__ */

kernel/bpf/Makefile

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@@ -4,6 +4,7 @@ obj-y := core.o 
obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o

obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o

obj-$(CONFIG_BPF_SYSCALL) += disasm.o

obj-$(CONFIG_BPF_SYSCALL) += btf.o

ifeq ($(CONFIG_NET),y)

obj-$(CONFIG_BPF_SYSCALL) += devmap.o

obj-$(CONFIG_BPF_SYSCALL) += cpumap.o

kernel/bpf/btf.c

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