1 /*
2 * DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
3 * Version 2, December 2004
4 *
5 * Copyright (C) 2016 Olaf Wintermann <olaf.wintermann@gmail.com>
6 *
7 * Everyone is permitted to copy and distribute verbatim or modified
8 * copies of this license document, and changing it is allowed as long
9 * as the name is changed.
10 *
11 * DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
12 * TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
13 *
14 * 0. You just DO WHAT THE FUCK YOU WANT TO.
15 */
16
17 /*
18 * compile instruction
19 * dependency: https://github.com/intelxed/xed
20 *
21 * export XED=/path/to/xed/installation
22 * cc -std=gnu99 -m64 -o x86dec -I$XED/include -L$XED/lib x86decode.c -lxed -lxed-ild
23 */
24
25 #include <stdio.h>
26 #include <stdlib.h>
27 #include <string.h>
28 #include <unistd.h>
29
30 #include <sys/mman.h>
31
32 #include <xed/xed-interface.h>
33 #include <xed/xed-common-hdrs.h>
34
35 #define MMAP_LEN 1024
36
37 typedef int(*fn)(int,int);
38 int func(int a, int b) {
39 return a + b;
40 }
41
42 int main(int argc, char **argv) {
43 xed_tables_init();
44
45 const xed_uint8_t *inst = (const xed_uint8_t*)func;
46
47 xed_decoded_inst_t dec;
48 xed_error_enum_t error;
49
50 char buffer[1024];
51
52 // allocate executable memory
53 void *execmem = mmap(NULL, MMAP_LEN, PROT_EXEC | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
54 if(!execmem) {
55 perror("mmap");
56 return -1;
57 }
58 char *em = execmem;
59
60 printf("copy function code:\n\n");
61 for(int i=0;i<256;i++) {
62 // init xed_decoded_inst_t struct
63 memset(&dec, '\0', sizeof(xed_decoded_inst_t));
64 xed_decoded_inst_set_mode(&dec, XED_MACHINE_MODE_LONG_64, XED_ADDRESS_WIDTH_64b);
65
66 // decode instruction
67 error = xed_decode(&dec, inst, 15);
68 if(error != XED_ERROR_NONE) {
69 // decode error
70 printf("%s\n", xed_error_enum_t2str(error));
71 break;
72 }
73
74 // print instruction
75 xed_format_context(XED_SYNTAX_ATT, &dec, buffer, 1024, 0, 0, 0);
76 printf("%s\n", buffer);
77
78 xed_uint_t instlen = xed_decoded_inst_get_length(&dec);
79
80 // copy instruction to new memory
81 memcpy(em, inst, instlen);
82 em += instlen;
83
84 // stop loop after any ret instruction
85 if(!memcmp("ret", buffer, 3)) {
86 break;
87 }
88
89 inst += instlen;
90 }
91
92 printf("\nexecute new code:\n\n");
93
94 fn f = (fn)execmem; // function pointer to execmem
95
96 int a = 10;
97 int b = 50;
98 int res = f(a, b); // run code from mmap memory
99
100 printf("f(%d, %d) = %d\n", a, b, res);
101
102 munmap(execmem, MMAP_LEN);
103
104 return 0;
105 }
106