/* From http://www.hanshq.net/making-executables.html */ #include #include #include #include #include static const uint8_t rot13_program[] = { /* read: */ 0xb9,0x00,0x20,0x00,0x00, /* movl $buffer,%ecx */ 0xb8,0x03,0x00,0x00,0x00, /* movl $3,%eax */ 0x68,0x00,0x10,0x00,0x00, /* pushl $4096 */ 0x51, /* pushl %ecx */ 0x6a,0x00, /* pushl $0 */ 0x6a,0x00, /* pushl $0 */ 0xcd,0x80, /* int $0x80 */ 0x83,0xc4,0x10, /* addl $16,%esp */ 0x85,0xc0, /* testl %eax,%eax */ 0x7e,0x25, /* jle end */ 0x89,0xc2, /* movl %eax,%edx */ /* rot13: */ 0x0f,0xb6,0x19, /* movzbl (%ecx),%ebx */ 0x8a,0x9b,0x2d,0x12,0x00,0x00, /* movb rot13_table(%ebx),%bl */ 0x88,0x19, /* movb %bl,(%ecx) */ 0x41, /* incl %ecx */ 0x48, /* decl %eax */ 0x75,0xf1, /* jnz rot13 */ 0x29,0xd1, /* subl %edx,%ecx */ 0xb8,0x04,0x00,0x00,0x00, /* movl $4,%eax */ 0x52, /* pushl %edx */ 0x51, /* pushl %ecx */ 0x6a,0x01, /* pushl $1 */ 0x6a,0x00, /* pushl $0 */ 0xcd,0x80, /* int $0x80 */ 0x83,0xc4,0x10, /* addl $16,%esp */ 0xeb,0xbe, /* jmp read */ /* end: */ 0xb8,0x01,0x00,0x00,0x00, /* movl $1,%eax */ 0x6a,0x00, /* pushl $0 */ 0x6a,0x00, /* pushl $0 */ 0xcd,0x80, /* int $0x80 */ }; static const uint8_t rot13_table[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 91, 92, 93, 94, 95, 96, 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255 }; /* Write an 8-bit value to file. */ static void write8(FILE *file, uint8_t value) { if (fputc(value, file) == EOF) { perror("fputc"); exit(1); } } /* Write a 32-bit value in little-endian to file. */ static void write32(FILE *file, uint32_t value) { write8(file, (value >> 0) & 0xff); write8(file, (value >> 8) & 0xff); write8(file, (value >> 16) & 0xff); write8(file, (value >> 24) & 0xff); } /* Write a string to file, padded to 16 bytes. */ static void writestr16(FILE *file, const char *str) { size_t len, i; len = strlen(str); assert(len <= 16 && "The string must fit in 16 bytes."); for (i = 0; i < 16; i++) { write8(file, i < len ? str[i] : 0); } } /* Seek to offset in file. */ static void seek(FILE *file, long offset) { if (fseek(file, offset, SEEK_SET) == -1) { perror("fseek"); exit(1); } } /* Round value up to alignment. */ static uint32_t align_to(uint32_t value, uint32_t alignment) { uint32_t remainder = value % alignment; if (remainder == 0) { return value; } return value + (alignment - remainder); } #define MACH_HEADER_SZ (7*4) /* Size of Mach-O header. */ #define MACH_SEGMENT_SZ (10*4+16) /* Size of segment struct. */ #define MACH_SECTION_SZ (2*16+9*4) /* Size of section struct. */ #define MACH_UNIXTHREAD_SZ (4*4+16*4) /* Size of UNIXTHREAD command. */ #define TEXT_SZ sizeof(rot13_program) /* Size of the code. */ #define CONST_SZ sizeof(rot13_table) /* Size of rot13_table. */ #define COMMON_SZ 4096 /* Size of buffer. */ #define PAGE_SIZE 4096 int main(int argc, char **argv) { FILE *f; size_t i; if (argc != 2) { fprintf(stderr, "Usage: %s \n", argv[0]); exit(1); } f = fopen(argv[1], "wb"); if (f == NULL) { perror("fopen"); exit(1); } uint32_t num_commands = 4; /* Three LC_SEGMENT and one LC_UNIXTHREAD. */ uint32_t commands_size = 3 * MACH_SEGMENT_SZ + 3 * MACH_SECTION_SZ + MACH_UNIXTHREAD_SZ; /* Mach-O header. */ write32(f, 0xfeedface); /* MH_MAGIC */ write32(f, 7); /* CPU_TYPE_I386 */ write32(f, 3); /* CPU_SUBTYPE_I386_ALL */ write32(f, 2); /* MH_EXECUTE */ write32(f, num_commands); /* ncmds */ write32(f, commands_size); /* sizeofcmds */ write32(f, 1); /* MH_NOUNDEFS */ /* The __PAGEZERO segment. */ write32(f, 1); /* LC_SEGMENT */ write32(f, MACH_SEGMENT_SZ); /* cmdsize */ writestr16(f, "__PAGEZERO"); /* segname */ write32(f, 0x0); /* vmaddr */ write32(f, 0x1000); /* vmsize */ write32(f, 0); /* fileoff */ write32(f, 0); /* filesize */ write32(f, 0); /* VM_PROT_NONE */ write32(f, 0); /* VM_PROT_NONE */ write32(f, 0); /* nsects */ write32(f, 0); /* flags */ uint32_t text_cmd_size = MACH_SEGMENT_SZ + 2 * MACH_SECTION_SZ; uint32_t text_seg_addr = 0x1000; uint32_t text_seg_size = align_to(MACH_HEADER_SZ + commands_size + TEXT_SZ + CONST_SZ, PAGE_SIZE); /* The __TEXT segment. */ write32(f, 1); /* LC_SEGMENT */ write32(f, text_cmd_size); /* cmdsize */ writestr16(f, "__TEXT"); /* segname */ write32(f, text_seg_addr); /* vmaddr */ write32(f, text_seg_size); /* vmsize */ write32(f, 0); /* fileoff */ write32(f, text_seg_size); /* filesize */ write32(f, 0x7); /* VM_PROT_ALL */ write32(f, 0x1 | 0x4); /* VM_PROT_READ | VM_PROT_EXECUTE */ write32(f, 2); /* nsects */ write32(f, 0); /* flags */ uint32_t text_sec_addr = text_seg_addr + MACH_HEADER_SZ + commands_size; uint32_t text_sec_size = TEXT_SZ; uint32_t text_sec_offset = MACH_HEADER_SZ + commands_size; /* The __TEXT,__text section. */ writestr16(f, "__text"); /* sectname */ writestr16(f, "__TEXT"); /* segname */ write32(f, text_sec_addr); /* addr */ write32(f, text_sec_size); /* size */ write32(f, text_sec_offset); /* offset */ write32(f, 0); /* alignment */ write32(f, 0); /* reloff */ write32(f, 0); /* nreloc */ write32(f, 0x80000400); /* S_ATTR_{SOME | PURE}_INSTRUCTIONS */ write32(f, 0); /* reserved1 */ write32(f, 0); /* reserved2 */ uint32_t const_sec_addr = text_sec_addr + text_sec_size; uint32_t const_sec_size = CONST_SZ; uint32_t const_sec_offset = text_sec_offset + text_sec_size; /* The __TEXT,__const section. */ writestr16(f, "__const"); /* sectname */ writestr16(f, "__TEXT"); /* segname */ write32(f, const_sec_addr); /* addr */ write32(f, const_sec_size); /* size */ write32(f, const_sec_offset); /* offset */ write32(f, 0); /* alignment */ write32(f, 0); /* reloff */ write32(f, 0); /* nreloc */ write32(f, 0); /* flags */ write32(f, 0); /* reserved1 */ write32(f, 0); /* reserved2 */ uint32_t data_cmd_size = MACH_SEGMENT_SZ + MACH_SECTION_SZ; uint32_t data_seg_addr = text_seg_addr + text_seg_size; assert(data_seg_addr == align_to(data_seg_addr, PAGE_SIZE)); uint32_t data_seg_size = COMMON_SZ; /* The __DATA segment. */ write32(f, 1); /* LC_SEGMENT */ write32(f, data_cmd_size); /* cmdsize */ writestr16(f, "__DATA"); /* segname */ write32(f, data_seg_addr); /* vmaddr */ write32(f, data_seg_size); /* vmsize */ write32(f, 0); /* fileoff */ write32(f, 0); /* filesize */ write32(f, 0x7); /* VM_PROT_ALL */ write32(f, 0x1 | 0x2); /* VM_PROT_READ | VM_PROT_WRITE */ write32(f, 1); /* nsects */ write32(f, 0); /* flags */ /* The __DATA,__common section. */ writestr16(f, "__common"); /* sectname */ writestr16(f, "__DATA"); /* segname */ write32(f, data_seg_addr); /* addr */ write32(f, data_seg_size); /* size */ write32(f, 0); /* offset */ write32(f, 0); /* alignment */ write32(f, 0); /* reloff */ write32(f, 0); /* nreloc */ write32(f, 0x1); /* S_ZEROFILL */ write32(f, 0); /* reserved1 */ write32(f, 0); /* reserved2 */ /* The LC_UNIXTHREAD command. */ write32(f, 0x5); /* LC_UNIXTHREAD */ write32(f, MACH_UNIXTHREAD_SZ); /* cmdsize */ write32(f, 1); /* flavor: X86_THREAD_STATE32 */ write32(f, 16); /* count: x86_THREAD_STATE_COUNT */ write32(f, 0x0); /* eax */ write32(f, 0x0); /* ebx */ write32(f, 0x0); /* ecx */ write32(f, 0x0); /* edx */ write32(f, 0x0); /* edi */ write32(f, 0x0); /* esi */ write32(f, 0x0); /* ebp */ write32(f, 0x0); /* esp */ write32(f, 0x0); /* ss */ write32(f, 0x0); /* eflags */ write32(f, text_sec_addr); /* eip */ write32(f, 0x0); /* cs */ write32(f, 0x0); /* ds */ write32(f, 0x0); /* es */ write32(f, 0x0); /* fs */ write32(f, 0x0); /* gs */ /* Write the __TEXT,__text section. */ for (i = 0; i < sizeof(rot13_program); i++) { write8(f, rot13_program[i]); } /* Write the __TEXT,__const section. */ for (i = 0; i < sizeof(rot13_table); i++) { write8(f, rot13_table[i]); } /* Pad the file to match the __TEXT segment size. */ assert(const_sec_offset + const_sec_size < text_seg_size); seek(f, text_seg_size - 1); write8(f, 0); if (fclose(f) == EOF) { perror("fclose"); exit(1); } return 0; }