/*
* BPF asm code parser
*
* This program is free software; you can distribute it and/or modify
* it under the terms of the GNU General Public License as published
* by the Free Software Foundation; either version 2 of the License,
* or (at your option) any later version.
*
* Syntax kept close to:
*
* Steven McCanne and Van Jacobson. 1993. The BSD packet filter: a new
* architecture for user-level packet capture. In Proceedings of the
* USENIX Winter 1993 Conference Proceedings on USENIX Winter 1993
* Conference Proceedings (USENIX'93). USENIX Association, Berkeley,
* CA, USA, 2-2.
*
* Copyright 2013 Daniel Borkmann <[email protected]>
* Licensed under the GNU General Public License, version 2.0 (GPLv2)
*/
%{
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdbool.h>
#include <unistd.h>
#include <errno.h>
#include <assert.h>
#include <linux/filter.h>
#include "bpf_exp.yacc.h"
enum jmp_type { JTL, JFL, JKL };
extern FILE *yyin;
extern int yylineno;
extern int yylex(void);
extern void yyerror(const char *str);
extern void bpf_asm_compile(FILE *fp, bool cstyle);
static void bpf_set_curr_instr(uint16_t op, uint8_t jt, uint8_t jf, uint32_t k);
static void bpf_set_curr_label(char *label);
static void bpf_set_jmp_label(char *label, enum jmp_type type);
%}
%union {
char *label;
uint32_t number;
}
%token OP_LDB OP_LDH OP_LD OP_LDX OP_ST OP_STX OP_JMP OP_JEQ OP_JGT OP_JGE
%token OP_JSET OP_ADD OP_SUB OP_MUL OP_DIV OP_AND OP_OR OP_XOR OP_LSH OP_RSH
%token OP_RET OP_TAX OP_TXA OP_LDXB OP_MOD OP_NEG OP_JNEQ OP_JLT OP_JLE OP_LDI
%token OP_LDXI
%token K_PKT_LEN
%token ':' ',' '[' ']' '(' ')' 'x' 'a' '+' 'M' '*' '&' '#' '%'
%token extension number label
%type <label> label
%type <number> extension
%type <number> number
%%
prog
: line
| prog line
;
line
: instr
| labelled_instr
;
labelled_instr
: labelled instr
;
instr
: ldb
| ldh
| ld
| ldi
| ldx
| ldxi
| st
| stx
| jmp
| jeq
| jneq
| jlt
| jle
| jgt
| jge
| jset
| add
| sub
| mul
| div
| mod
| neg
| and
| or
| xor
| lsh
| rsh
| ret
| tax
| txa
;
labelled
: label ':' { bpf_set_curr_label($1); }
;
ldb
: OP_LDB '[' 'x' '+' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_B | BPF_IND, 0, 0, $5); }
| OP_LDB '[' '%' 'x' '+' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_B | BPF_IND, 0, 0, $6); }
| OP_LDB '[' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0, $3); }
| OP_LDB extension {
bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
SKF_AD_OFF + $2); }
;
ldh
: OP_LDH '[' 'x' '+' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_H | BPF_IND, 0, 0, $5); }
| OP_LDH '[' '%' 'x' '+' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_H | BPF_IND, 0, 0, $6); }
| OP_LDH '[' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0, $3); }
| OP_LDH extension {
bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
SKF_AD_OFF + $2); }
;
ldi
: OP_LDI '#' number {
bpf_set_curr_instr(BPF_LD | BPF_IMM, 0, 0, $3); }
| OP_LDI number {
bpf_set_curr_instr(BPF_LD | BPF_IMM, 0, 0, $2); }
;
ld
: OP_LD '#' number {
bpf_set_curr_instr(BPF_LD | BPF_IMM, 0, 0, $3); }
| OP_LD K_PKT_LEN {
bpf_set_curr_instr(BPF_LD | BPF_W | BPF_LEN, 0, 0, 0); }
| OP_LD extension {
bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
SKF_AD_OFF + $2); }
| OP_LD 'M' '[' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_MEM, 0, 0, $4); }
| OP_LD '[' 'x' '+' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_W | BPF_IND, 0, 0, $5); }
| OP_LD '[' '%' 'x' '+' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_W | BPF_IND, 0, 0, $6); }
| OP_LD '[' number ']' {
bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0, $3); }
;
ldxi
: OP_LDXI '#' number {
bpf_set_curr_instr(BPF_LDX | BPF_IMM, 0, 0, $3); }
| OP_LDXI number {
bpf_set_curr_instr(BPF_LDX | BPF_IMM, 0, 0, $2); }
;
ldx
: OP_LDX '#' number {
bpf_set_curr_instr(BPF_LDX | BPF_IMM, 0, 0, $3); }
| OP_LDX K_PKT_LEN {
bpf_set_curr_instr(BPF_LDX | BPF_W | BPF_LEN, 0, 0, 0); }
| OP_LDX 'M' '[' number ']' {
bpf_set_curr_instr(BPF_LDX | BPF_MEM, 0, 0, $4); }
| OP_LDXB number '*' '(' '[' number ']' '&' number ')' {
if ($2 != 4 || $9 != 0xf) {
fprintf(stderr, "ldxb offset not supported!\n");
exit(1);
} else {
bpf_set_curr_instr(BPF_LDX | BPF_MSH | BPF_B, 0, 0, $6); } }
| OP_LDX number '*' '(' '[' number ']' '&' number ')' {
if ($2 != 4 || $9 != 0xf) {
fprintf(stderr, "ldxb offset not supported!\n");
exit(1);
} else {
bpf_set_curr_instr(BPF_LDX | BPF_MSH | BPF_B, 0, 0, $6); } }
;
st
: OP_ST 'M' '[' number ']' {
bpf_set_curr_instr(BPF_ST, 0, 0, $4); }
;
stx
: OP_STX 'M' '[' number ']' {
bpf_set_curr_instr(BPF_STX, 0, 0, $4); }
;
jmp
: OP_JMP label {
bpf_set_jmp_label($2, JKL);
bpf_set_curr_instr(BPF_JMP | BPF_JA, 0, 0, 0); }
;
jeq
: OP_JEQ '#' number ',' label ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_jmp_label($7, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, $3); }
| OP_JEQ 'x' ',' label ',' label {
bpf_set_jmp_label($4, JTL);
bpf_set_jmp_label($6, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_X, 0, 0, 0); }
| OP_JEQ '%' 'x' ',' label ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_jmp_label($7, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_X, 0, 0, 0); }
| OP_JEQ '#' number ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, $3); }
| OP_JEQ 'x' ',' label {
bpf_set_jmp_label($4, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_X, 0, 0, 0); }
| OP_JEQ '%' 'x' ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_X, 0, 0, 0); }
;
jneq
: OP_JNEQ '#' number ',' label {
bpf_set_jmp_label($5, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, $3); }
| OP_JNEQ 'x' ',' label {
bpf_set_jmp_label($4, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_X, 0, 0, 0); }
| OP_JNEQ '%' 'x' ',' label {
bpf_set_jmp_label($5, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JEQ | BPF_X, 0, 0, 0); }
;
jlt
: OP_JLT '#' number ',' label {
bpf_set_jmp_label($5, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_K, 0, 0, $3); }
| OP_JLT 'x' ',' label {
bpf_set_jmp_label($4, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_X, 0, 0, 0); }
| OP_JLT '%' 'x' ',' label {
bpf_set_jmp_label($5, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_X, 0, 0, 0); }
;
jle
: OP_JLE '#' number ',' label {
bpf_set_jmp_label($5, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_K, 0, 0, $3); }
| OP_JLE 'x' ',' label {
bpf_set_jmp_label($4, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_X, 0, 0, 0); }
| OP_JLE '%' 'x' ',' label {
bpf_set_jmp_label($5, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_X, 0, 0, 0); }
;
jgt
: OP_JGT '#' number ',' label ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_jmp_label($7, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_K, 0, 0, $3); }
| OP_JGT 'x' ',' label ',' label {
bpf_set_jmp_label($4, JTL);
bpf_set_jmp_label($6, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_X, 0, 0, 0); }
| OP_JGT '%' 'x' ',' label ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_jmp_label($7, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_X, 0, 0, 0); }
| OP_JGT '#' number ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_K, 0, 0, $3); }
| OP_JGT 'x' ',' label {
bpf_set_jmp_label($4, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_X, 0, 0, 0); }
| OP_JGT '%' 'x' ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JGT | BPF_X, 0, 0, 0); }
;
jge
: OP_JGE '#' number ',' label ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_jmp_label($7, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_K, 0, 0, $3); }
| OP_JGE 'x' ',' label ',' label {
bpf_set_jmp_label($4, JTL);
bpf_set_jmp_label($6, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_X, 0, 0, 0); }
| OP_JGE '%' 'x' ',' label ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_jmp_label($7, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_X, 0, 0, 0); }
| OP_JGE '#' number ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_K, 0, 0, $3); }
| OP_JGE 'x' ',' label {
bpf_set_jmp_label($4, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_X, 0, 0, 0); }
| OP_JGE '%' 'x' ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JGE | BPF_X, 0, 0, 0); }
;
jset
: OP_JSET '#' number ',' label ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_jmp_label($7, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JSET | BPF_K, 0, 0, $3); }
| OP_JSET 'x' ',' label ',' label {
bpf_set_jmp_label($4, JTL);
bpf_set_jmp_label($6, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JSET | BPF_X, 0, 0, 0); }
| OP_JSET '%' 'x' ',' label ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_jmp_label($7, JFL);
bpf_set_curr_instr(BPF_JMP | BPF_JSET | BPF_X, 0, 0, 0); }
| OP_JSET '#' number ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JSET | BPF_K, 0, 0, $3); }
| OP_JSET 'x' ',' label {
bpf_set_jmp_label($4, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JSET | BPF_X, 0, 0, 0); }
| OP_JSET '%' 'x' ',' label {
bpf_set_jmp_label($5, JTL);
bpf_set_curr_instr(BPF_JMP | BPF_JSET | BPF_X, 0, 0, 0); }
;
add
: OP_ADD '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_ADD | BPF_K, 0, 0, $3); }
| OP_ADD 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_ADD | BPF_X, 0, 0, 0); }
| OP_ADD '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_ADD | BPF_X, 0, 0, 0); }
;
sub
: OP_SUB '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_SUB | BPF_K, 0, 0, $3); }
| OP_SUB 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_SUB | BPF_X, 0, 0, 0); }
| OP_SUB '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_SUB | BPF_X, 0, 0, 0); }
;
mul
: OP_MUL '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_MUL | BPF_K, 0, 0, $3); }
| OP_MUL 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_MUL | BPF_X, 0, 0, 0); }
| OP_MUL '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_MUL | BPF_X, 0, 0, 0); }
;
div
: OP_DIV '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_DIV | BPF_K, 0, 0, $3); }
| OP_DIV 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_DIV | BPF_X, 0, 0, 0); }
| OP_DIV '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_DIV | BPF_X, 0, 0, 0); }
;
mod
: OP_MOD '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_MOD | BPF_K, 0, 0, $3); }
| OP_MOD 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_MOD | BPF_X, 0, 0, 0); }
| OP_MOD '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_MOD | BPF_X, 0, 0, 0); }
;
neg
: OP_NEG {
bpf_set_curr_instr(BPF_ALU | BPF_NEG, 0, 0, 0); }
;
and
: OP_AND '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_AND | BPF_K, 0, 0, $3); }
| OP_AND 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_AND | BPF_X, 0, 0, 0); }
| OP_AND '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_AND | BPF_X, 0, 0, 0); }
;
or
: OP_OR '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_OR | BPF_K, 0, 0, $3); }
| OP_OR 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_OR | BPF_X, 0, 0, 0); }
| OP_OR '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_OR | BPF_X, 0, 0, 0); }
;
xor
: OP_XOR '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_XOR | BPF_K, 0, 0, $3); }
| OP_XOR 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_XOR | BPF_X, 0, 0, 0); }
| OP_XOR '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_XOR | BPF_X, 0, 0, 0); }
;
lsh
: OP_LSH '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_LSH | BPF_K, 0, 0, $3); }
| OP_LSH 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_LSH | BPF_X, 0, 0, 0); }
| OP_LSH '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_LSH | BPF_X, 0, 0, 0); }
;
rsh
: OP_RSH '#' number {
bpf_set_curr_instr(BPF_ALU | BPF_RSH | BPF_K, 0, 0, $3); }
| OP_RSH 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_RSH | BPF_X, 0, 0, 0); }
| OP_RSH '%' 'x' {
bpf_set_curr_instr(BPF_ALU | BPF_RSH | BPF_X, 0, 0, 0); }
;
ret
: OP_RET 'a' {
bpf_set_curr_instr(BPF_RET | BPF_A, 0, 0, 0); }
| OP_RET '%' 'a' {
bpf_set_curr_instr(BPF_RET | BPF_A, 0, 0, 0); }
| OP_RET 'x' {
bpf_set_curr_instr(BPF_RET | BPF_X, 0, 0, 0); }
| OP_RET '%' 'x' {
bpf_set_curr_instr(BPF_RET | BPF_X, 0, 0, 0); }
| OP_RET '#' number {
bpf_set_curr_instr(BPF_RET | BPF_K, 0, 0, $3); }
;
tax
: OP_TAX {
bpf_set_curr_instr(BPF_MISC | BPF_TAX, 0, 0, 0); }
;
txa
: OP_TXA {
bpf_set_curr_instr(BPF_MISC | BPF_TXA, 0, 0, 0); }
;
%%
static int curr_instr = 0;
static struct sock_filter out[BPF_MAXINSNS];
static char **labels, **labels_jt, **labels_jf, **labels_k;
static void bpf_assert_max(void)
{
if (curr_instr >= BPF_MAXINSNS) {
fprintf(stderr, "only max %u insns allowed!\n", BPF_MAXINSNS);
exit(1);
}
}
static void bpf_set_curr_instr(uint16_t code, uint8_t jt, uint8_t jf,
uint32_t k)
{
bpf_assert_max();
out[curr_instr].code = code;
out[curr_instr].jt = jt;
out[curr_instr].jf = jf;
out[curr_instr].k = k;
curr_instr++;
}
static void bpf_set_curr_label(char *label)
{
bpf_assert_max();
labels[curr_instr] = label;
}
static void bpf_set_jmp_label(char *label, enum jmp_type type)
{
bpf_assert_max();
switch (type) {
case JTL:
labels_jt[curr_instr] = label;
break;
case JFL:
labels_jf[curr_instr] = label;
break;
case JKL:
labels_k[curr_instr] = label;
break;
}
}
static int bpf_find_insns_offset(const char *label)
{
int i, max = curr_instr, ret = -ENOENT;
for (i = 0; i < max; i++) {
if (labels[i] && !strcmp(label, labels[i])) {
ret = i;
break;
}
}
if (ret == -ENOENT) {
fprintf(stderr, "no such label \'%s\'!\n", label);
exit(1);
}
return ret;
}
static void bpf_stage_1_insert_insns(void)
{
yyparse();
}
static void bpf_reduce_k_jumps(void)
{
int i;
for (i = 0; i < curr_instr; i++) {
if (labels_k[i]) {
int off = bpf_find_insns_offset(labels_k[i]);
out[i].k = (uint32_t) (off - i - 1);
}
}
}
static uint8_t bpf_encode_jt_jf_offset(int off, int i)
{
int delta = off - i - 1;
if (delta < 0 || delta > 255) {
fprintf(stderr, "error: insn #%d jumps to insn #%d, "
"which is out of range\n", i, off);
exit(1);
}
return (uint8_t) delta;
}
static void bpf_reduce_jt_jumps(void)
{
int i;
for (i = 0; i < curr_instr; i++) {
if (labels_jt[i]) {
int off = bpf_find_insns_offset(labels_jt[i]);
out[i].jt = bpf_encode_jt_jf_offset(off, i);
}
}
}
static void bpf_reduce_jf_jumps(void)
{
int i;
for (i = 0; i < curr_instr; i++) {
if (labels_jf[i]) {
int off = bpf_find_insns_offset(labels_jf[i]);
out[i].jf = bpf_encode_jt_jf_offset(off, i);
}
}
}
static void bpf_stage_2_reduce_labels(void)
{
bpf_reduce_k_jumps();
bpf_reduce_jt_jumps();
bpf_reduce_jf_jumps();
}
static void bpf_pretty_print_c(void)
{
int i;
for (i = 0; i < curr_instr; i++)
printf("{ %#04x, %2u, %2u, %#010x },\n", out[i].code,
out[i].jt, out[i].jf, out[i].k);
}
static void bpf_pretty_print(void)
{
int i;
printf("%u,", curr_instr);
for (i = 0; i < curr_instr; i++)
printf("%u %u %u %u,", out[i].code,
out[i].jt, out[i].jf, out[i].k);
printf("\n");
}
static void bpf_init(void)
{
memset(out, 0, sizeof(out));
labels = calloc(BPF_MAXINSNS, sizeof(*labels));
assert(labels);
labels_jt = calloc(BPF_MAXINSNS, sizeof(*labels_jt));
assert(labels_jt);
labels_jf = calloc(BPF_MAXINSNS, sizeof(*labels_jf));
assert(labels_jf);
labels_k = calloc(BPF_MAXINSNS, sizeof(*labels_k));
assert(labels_k);
}
static void bpf_destroy_labels(void)
{
int i;
for (i = 0; i < curr_instr; i++) {
free(labels_jf[i]);
free(labels_jt[i]);
free(labels_k[i]);
free(labels[i]);
}
}
static void bpf_destroy(void)
{
bpf_destroy_labels();
free(labels_jt);
free(labels_jf);
free(labels_k);
free(labels);
}
void bpf_asm_compile(FILE *fp, bool cstyle)
{
yyin = fp;
bpf_init();
bpf_stage_1_insert_insns();
bpf_stage_2_reduce_labels();
bpf_destroy();
if (cstyle)
bpf_pretty_print_c();
else
bpf_pretty_print();
if (fp != stdin)
fclose(yyin);
}
void yyerror(const char *str)
{
fprintf(stderr, "error: %s at line %d\n", str, yylineno);
exit(1);
}
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