Commit c4d0bfb4 authored by Alan Maguire's avatar Alan Maguire Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_snprintf_btf helper 



A helper is added to support tracing kernel type information in BPF
using the BPF Type Format (BTF).  Its signature is

long bpf_snprintf_btf(char *str, u32 str_size, struct btf_ptr *ptr,
		      u32 btf_ptr_size, u64 flags);

struct btf_ptr * specifies

- a pointer to the data to be traced
- the BTF id of the type of data pointed to
- a flags field is provided for future use; these flags
  are not to be confused with the BTF_F_* flags
  below that control how the btf_ptr is displayed; the
  flags member of the struct btf_ptr may be used to
  disambiguate types in kernel versus module BTF, etc;
  the main distinction is the flags relate to the type
  and information needed in identifying it; not how it
  is displayed.

For example a BPF program with a struct sk_buff *skb
could do the following:

	static struct btf_ptr b = { };

	b.ptr = skb;
	b.type_id = __builtin_btf_type_id(struct sk_buff, 1);
	bpf_snprintf_btf(str, sizeof(str), &b, sizeof(b), 0, 0);

Default output looks like this:

(struct sk_buff){
 .transport_header = (__u16)65535,
 .mac_header = (__u16)65535,
 .end = (sk_buff_data_t)192,
 .head = (unsigned char *)0x000000007524fd8b,
 .data = (unsigned char *)0x000000007524fd8b,
 .truesize = (unsigned int)768,
 .users = (refcount_t){
  .refs = (atomic_t){
   .counter = (int)1,
  },
 },
}

Flags modifying display are as follows:

- BTF_F_COMPACT:	no formatting around type information
- BTF_F_NONAME:		no struct/union member names/types
- BTF_F_PTR_RAW:	show raw (unobfuscated) pointer values;
			equivalent to %px.
- BTF_F_ZERO:		show zero-valued struct/union members;
			they are not displayed by default

Signed-off-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1601292670-1616-4-git-send-email-alan.maguire@oracle.com
parent 31d0bc81

include/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -1822,6 +1822,7 @@ extern const struct bpf_func_proto bpf_skc_to_tcp_timewait_sock_proto; 
extern const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto;

extern const struct bpf_func_proto bpf_skc_to_udp6_sock_proto;

extern const struct bpf_func_proto bpf_copy_from_user_proto;

extern const struct bpf_func_proto bpf_snprintf_btf_proto;



const struct bpf_func_proto *bpf_tracing_func_proto(

	enum bpf_func_id func_id, const struct bpf_prog *prog);

include/linux/btf.h

+5 −4
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 


#include <linux/types.h>

#include <uapi/linux/btf.h>

#include <uapi/linux/bpf.h>



#define BTF_TYPE_EMIT(type) ((void)(type *)0)
@@ -59,10 +60,10 @@ const struct btf_type *btf_type_id_size(const struct btf *btf, 
 *	- BTF_SHOW_UNSAFE: skip use of bpf_probe_read() to safely read

 *	  data before displaying it.

 */

#define BTF_SHOW_COMPACT	(1ULL << 0)

#define BTF_SHOW_NONAME		(1ULL << 1)

#define BTF_SHOW_PTR_RAW	(1ULL << 2)

#define BTF_SHOW_ZERO		(1ULL << 3)

#define BTF_SHOW_COMPACT	BTF_F_COMPACT

#define BTF_SHOW_NONAME		BTF_F_NONAME

#define BTF_SHOW_PTR_RAW	BTF_F_PTR_RAW

#define BTF_SHOW_ZERO		BTF_F_ZERO

#define BTF_SHOW_UNSAFE		(1ULL << 4)



void btf_type_seq_show(const struct btf *btf, u32 type_id, void *obj,

include/uapi/linux/bpf.h

+67 −0
Original line number Diff line number Diff line
@@ -3594,6 +3594,42 @@ union bpf_attr { 
 * 		the data in *dst*. This is a wrapper of **copy_from_user**\ ().

 * 	Return

 * 		0 on success, or a negative error in case of failure.

 *

 * long bpf_snprintf_btf(char *str, u32 str_size, struct btf_ptr *ptr, u32 btf_ptr_size, u64 flags)

 *	Description

 *		Use BTF to store a string representation of *ptr*->ptr in *str*,

 *		using *ptr*->type_id.  This value should specify the type

 *		that *ptr*->ptr points to. LLVM __builtin_btf_type_id(type, 1)

 *		can be used to look up vmlinux BTF type ids. Traversing the

 *		data structure using BTF, the type information and values are

 *		stored in the first *str_size* - 1 bytes of *str*.  Safe copy of

 *		the pointer data is carried out to avoid kernel crashes during

 *		operation.  Smaller types can use string space on the stack;

 *		larger programs can use map data to store the string

 *		representation.

 *

 *		The string can be subsequently shared with userspace via

 *		bpf_perf_event_output() or ring buffer interfaces.

 *		bpf_trace_printk() is to be avoided as it places too small

 *		a limit on string size to be useful.

 *

 *		*flags* is a combination of

 *

 *		**BTF_F_COMPACT**

 *			no formatting around type information

 *		**BTF_F_NONAME**

 *			no struct/union member names/types

 *		**BTF_F_PTR_RAW**

 *			show raw (unobfuscated) pointer values;

 *			equivalent to printk specifier %px.

 *		**BTF_F_ZERO**

 *			show zero-valued struct/union members; they

 *			are not displayed by default

 *

 *	Return

 *		The number of bytes that were written (or would have been

 *		written if output had to be truncated due to string size),

 *		or a negative error in cases of failure.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -3745,6 +3781,7 @@ union bpf_attr { 
	FN(inode_storage_delete),	\

	FN(d_path),			\

	FN(copy_from_user),		\

	FN(snprintf_btf),		\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4853,4 +4890,34 @@ struct bpf_sk_lookup { 
	__u32 local_port;	/* Host byte order */

};



/*

 * struct btf_ptr is used for typed pointer representation; the

 * type id is used to render the pointer data as the appropriate type

 * via the bpf_snprintf_btf() helper described above.  A flags field -

 * potentially to specify additional details about the BTF pointer

 * (rather than its mode of display) - is included for future use.

 * Display flags - BTF_F_* - are passed to bpf_snprintf_btf separately.

 */

struct btf_ptr {

	void *ptr;

	__u32 type_id;

	__u32 flags;		/* BTF ptr flags; unused at present. */

};



/*

 * Flags to control bpf_snprintf_btf() behaviour.

 *     - BTF_F_COMPACT: no formatting around type information

 *     - BTF_F_NONAME: no struct/union member names/types

 *     - BTF_F_PTR_RAW: show raw (unobfuscated) pointer values;

 *       equivalent to %px.

 *     - BTF_F_ZERO: show zero-valued struct/union members; they

 *       are not displayed by default

 */

enum {

	BTF_F_COMPACT	=	(1ULL << 0),

	BTF_F_NONAME	=	(1ULL << 1),

	BTF_F_PTR_RAW	=	(1ULL << 2),

	BTF_F_ZERO	=	(1ULL << 3),

};



#endif /* _UAPI__LINUX_BPF_H__ */

kernel/bpf/core.c

+1 −0
Original line number Diff line number Diff line
@@ -2216,6 +2216,7 @@ const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak; 
const struct bpf_func_proto bpf_get_current_ancestor_cgroup_id_proto __weak;

const struct bpf_func_proto bpf_get_local_storage_proto __weak;

const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto __weak;

const struct bpf_func_proto bpf_snprintf_btf_proto __weak;



const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)

{

kernel/bpf/helpers.c

+4 −0
Original line number Diff line number Diff line
@@ -683,6 +683,10 @@ bpf_base_func_proto(enum bpf_func_id func_id) 
		if (!perfmon_capable())

			return NULL;

		return bpf_get_trace_printk_proto();

	case BPF_FUNC_snprintf_btf:

		if (!perfmon_capable())

			return NULL;

		return &bpf_snprintf_btf_proto;

	case BPF_FUNC_jiffies64:

		return &bpf_jiffies64_proto;

	default: