diff options
| -rw-r--r-- | example/samples/dse_crackme.c | 104 | ||||
| -rw-r--r-- | example/symbol_exec/dse_crackme.py | 310 | ||||
| -rwxr-xr-x | test/test_all.py | 11 |
3 files changed, 425 insertions, 0 deletions
diff --git a/example/samples/dse_crackme.c b/example/samples/dse_crackme.c new file mode 100644 index 00000000..5fc0faaf --- /dev/null +++ b/example/samples/dse_crackme.c @@ -0,0 +1,104 @@ +#include <stdio.h> +#include <stdint.h> + +/* + * This example is a tiny crackme, with a few specificities: + * - the flag must be read from a file ('test.txt') + * - a few steps are not naively bruteforcable (using a fuzzer for instance): + * comparison with a 32bit value, then CRC16 + * - a DSE engine has to support the search into a fixed memory table + * (crc16_tab) based on variables (file bytes) +*/ + + +static const uint16_t crc16_tab[] = { + 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, + 0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, + 0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6, + 0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, + 0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485, + 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d, + 0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4, + 0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc, + 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823, + 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, + 0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12, + 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a, + 0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41, + 0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49, + 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70, + 0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, + 0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f, + 0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067, + 0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e, + 0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256, + 0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d, + 0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, + 0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c, + 0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634, + 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab, + 0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3, + 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a, + 0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92, + 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, + 0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1, + 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, + 0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0, +}; + +uint16_t crc16(uint16_t seed, unsigned char *buf, size_t len) +{ + size_t i; + uint16_t tmp; + + tmp = seed ^ 0xFFFFFFFF; + for (i = 0; i < len; i++) { + tmp = crc16_tab[((tmp>>8) ^ buf[i]) & 0xFF] ^ (tmp << 8); + } + return tmp; +} + +uint16_t test() { + FILE *file; + unsigned char buf[0x100] = {0}; + size_t read; + uint32_t temp; + + file = fopen("test.txt", "r"); + if (file) { + read = fread(buf, sizeof(char), 0x100, file); + fclose(file); + if (read < 14) { + return 0xFFFF; + } + if (buf[0] != 'M') { + return 0xFFFF; + } + if (!((unsigned char) (2 * buf[7]) == 14) || (buf[7] == 7)) { + return 0xFFFF; + } + temp = buf[1]; + temp <<= 8; + temp |= buf[2]; + temp <<= 8; + temp |= buf[3]; + temp <<= 8; + temp |= buf[4]; + if (temp != 0x2140244d) { // "!@$M" + return 0xFFFF; + } + return crc16(0, buf, read); + } else { + return 0xFFFF; + } +} + +int main(int argc, char** argv) { + uint16_t result = test(); + if (result == 0x1337) { + printf("OK\n"); + } else { + printf("BAD\n"); + } + return 0; +} diff --git a/example/symbol_exec/dse_crackme.py b/example/symbol_exec/dse_crackme.py new file mode 100644 index 00000000..e08536f9 --- /dev/null +++ b/example/symbol_exec/dse_crackme.py @@ -0,0 +1,310 @@ +"""Example of DynamicSymbolicExecution engine use + +This example should run on the compiled ELF x86 64bits version of +"dse_crackme.c" + +""" + +#### This part is only related to the run of the sample, without DSE #### +import os +import subprocess +from collections import namedtuple +from pdb import pm + +from miasm2.jitter.csts import PAGE_READ, PAGE_WRITE +from miasm2.analysis.sandbox import Sandbox_Linux_x86_64 +from miasm2.expression.expression import * + +# File "management" +my_FILE_ptr = 0x11223344 +FInfo = namedtuple("FInfo", ["path", "fdesc"]) +FILE_to_info = {} +def xxx_fopen(jitter): + ''' + #include <stdio.h> + + FILE *fopen(const char *path, const char *mode); + ''' + global my_FILE_ptr + ret_addr, args = jitter.func_args_systemv(['path', 'mode']) + fname = jitter.get_str_ansi(args.path) + FILE_to_info[my_FILE_ptr] = FInfo(fname, open(fname)) + my_FILE_ptr += 1 + return jitter.func_ret_stdcall(ret_addr, my_FILE_ptr - 1) + +def xxx_fread(jitter): + ''' + #include <stdio.h> + + size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream); + ''' + ret_addr, args = jitter.func_args_systemv(['ptr', 'size', 'nmemb', 'stream']) + info = FILE_to_info[args.stream] + data = info.fdesc.read(args.size * args.nmemb) + jitter.vm.set_mem(args.ptr, data) + return jitter.func_ret_stdcall(ret_addr, len(data)) + +def xxx_fclose(jitter): + ''' + #include <stdio.h> + + int fclose(FILE *stream); + ''' + ret_addr, args = jitter.func_args_systemv(['stream']) + del FILE_to_info[args.stream] + return jitter.func_ret_stdcall(ret_addr, 0) + +# Create sandbox +parser = Sandbox_Linux_x86_64.parser(description="ELF sandboxer") +parser.add_argument("filename", help="ELF Filename") +options = parser.parse_args() +options.mimic_env = True +sb = Sandbox_Linux_x86_64(options.filename, options, globals()) + +# Init segment +sb.jitter.ir_arch.do_stk_segm = True +sb.jitter.ir_arch.do_ds_segm = True +sb.jitter.ir_arch.do_str_segm = True +sb.jitter.ir_arch.do_all_segm = True +FS_0_ADDR = 0x7ff70000 +sb.jitter.cpu.FS = 0x4 +sb.jitter.cpu.set_segm_base(sb.jitter.cpu.FS, FS_0_ADDR) +sb.jitter.vm.add_memory_page( + FS_0_ADDR + 0x28, PAGE_READ, "\x42\x42\x42\x42\x42\x42\x42\x42", + "Stack canary FS[0x28]") + +# Prepare the execution +sb.jitter.init_run(sb.entry_point) + + +#### This part handle the DSE #### +from miasm2.analysis.dse import DSEPathConstraint +from miasm2.analysis.machine import Machine + + +# File "management" + +class SymbolicFile(object): + """Symbolic file with read operation, returning symbolic bytes""" + + def __init__(self, fname): + self.fname = fname + self.position = 0 + self.max_size = os.stat(fname).st_size + self.gen_bytes = {} + self.state = "OPEN" + + def read(self, length): + assert self.state == "OPEN" + out = [] + for i in xrange(self.position, min(self.position + length, + self.max_size)): + if i not in self.gen_bytes: + ret = ExprId("SF_%08x_%d" % (id(self), i), 8) + self.gen_bytes[i] = ret + out.append(self.gen_bytes[i]) + self.position += 1 + + return out + + def close(self): + self.state = "CLOSE" + + +FILE_to_info_symb = {} +FILE_stream = ExprId("FILE_0", 64) +FILE_size = ExprId("FILE_0_size", 64) + +def xxx_fopen_symb(dse): + regs = dse.ir_arch.arch.regs + fname_addr = dse.eval_expr(regs.RDI) + mode = dse.eval_expr(regs.RSI) + assert fname_addr.is_int() + assert mode.is_int() + fname = dse.jitter.get_str_ansi(int(fname_addr)) + ret_addr = ExprInt(dse.jitter.get_stack_arg(0), regs.RIP.size) + + assert len(FILE_to_info_symb) == 0 + ret_value = FILE_stream + FILE_to_info_symb[ret_value] = SymbolicFile(fname) + + dse.update_state({ + regs.RSP: dse.eval_expr(regs.RSP + ExprInt(8, regs.RSP.size)), + dse.ir_arch.IRDst: ret_addr, + regs.RIP: ret_addr, + regs.RAX: ret_value, + }) + +def xxx_fread_symb(dse): + regs = dse.ir_arch.arch.regs + ptr = dse.eval_expr(regs.RDI) + size = dse.eval_expr(regs.RSI) + nmemb = dse.eval_expr(regs.RDX) + stream = dse.eval_expr(regs.RCX) + + assert size.is_int() + assert nmemb.is_int() + + # Fill the buffer with symbolic bytes + update = {} + sf = FILE_to_info_symb[stream] + data = sf.read(int(size) * int(nmemb)) + for i, content in enumerate(data): + addr = dse.symb.expr_simp(ptr + ExprInt(i, ptr.size)) + update[ExprMem(addr, 8)] = content + + ret_addr = ExprInt(dse.jitter.get_stack_arg(0), regs.RIP.size) + ret_value = FILE_size + + update.update({ + regs.RSP: dse.symb.eval_expr(regs.RSP + ExprInt(8, regs.RSP.size)), + dse.ir_arch.IRDst: ret_addr, + regs.RIP: ret_addr, + regs.RAX: ret_value, + }) + dse.update_state(update) + +def xxx_fclose_symb(dse): + regs = dse.ir_arch.arch.regs + stream = dse.eval_expr(regs.RDI) + FILE_to_info_symb[stream].close() + + ret_addr = ExprInt(dse.jitter.get_stack_arg(0), regs.RIP.size) + dse.update_state({ + regs.RSP: dse.symb.eval_expr(regs.RSP + ExprInt(8, regs.RSP.size)), + dse.ir_arch.IRDst: ret_addr, + regs.RIP: ret_addr, + regs.RAX: ExprInt(0, regs.RAX.size), + }) + +# Symbolic naive version of _libc_start_main + +def xxx___libc_start_main_symb(dse): + # ['RDI', 'RSI', 'RDX', 'RCX', 'R8', 'R9'] + # main, argc, argv, ... + regs = dse.ir_arch.arch.regs + top_stack = dse.eval_expr(regs.RSP) + main_addr = dse.eval_expr(regs.RDI) + argc = dse.eval_expr(regs.RSI) + argv = dse.eval_expr(regs.RDX) + hlt_addr = ExprInt(0x1337beef, 64) + + dse.update_state({ + ExprMem(top_stack, 64): hlt_addr, + regs.RDI: argc, + regs.RSI: argv, + dse.ir_arch.IRDst: main_addr, + dse.ir_arch.pc: main_addr, + }) + +# Stop the execution on puts and get back the corresponding string +class FinnishOn(Exception): + + def __init__(self, string): + self.string = string + super(FinnishOn, self).__init__() + +def xxx_puts_symb(dse): + string = dse.jitter.get_str_ansi(dse.jitter.cpu.RDI) + raise FinnishOn(string) + + +done = set([]) # Set of jump address already handled +todo = set([""]) # Set of file content to test + +class DSEGenFile(DSEPathConstraint): + """DSE with a specific solution creation: + The solution is the content of the FILE to be read + + The politics of exploration is the branch coverage: create a solution only + if the target address has never been seen + """ + + def handle_solution(self, model, destination): + global todo, done + assert destination.is_int() + + if destination in done: + # Skip this path, already treated + return + + finfo = FILE_to_info_symb[FILE_stream] + + # Build corresponding file + out = "" + fsize = max(model.eval(self.z3_trans.from_expr(FILE_size)).as_long(), + len(finfo.gen_bytes)) + for index in xrange(fsize): + try: + byteid = finfo.gen_bytes[index] + out += chr(model.eval(self.z3_trans.from_expr(byteid)).as_long()) + except (KeyError, AttributeError) as _: + # Default value if there is no constraint on current byte + out += "\x00" + + todo.add(out) + done.add(destination) + +# Instanciate the DSE engine +machine = Machine("x86_64") +dse = DSEGenFile(machine) + +# Attach to the jitter +dse.attach(sb.jitter) + +# Update the jitter state: df is read, but never set +# Approachs: specific or generic +# - Specific: +# df_value = ExprInt(sb.jitter.cpu.df, dse.ir_arch.arch.regs.df.size) +# dse.update_state({ +# dse.ir_arch.arch.regs.df: df_value +# }) +# - Generic: +dse.update_state_from_concrete() + +# Add constraint on file size, we don't want to generate too big FILE +z3_file_size = dse.z3_trans.from_expr(FILE_size) +dse.cur_solver.add(0 < z3_file_size) +dse.cur_solver.add(z3_file_size < 0x10) + +# Register symbolic stubs for extern functions (xxx_puts_symb, ...) +dse.add_lib_handler(sb.libs, globals()) + +# Automatic exploration of solution + +## Save the current clean state, before any computation of the FILE content +snapshot = dse.take_snapshot() +found = False + +while todo: + # Prepare a solution to try, based on the clean state + file_content = todo.pop() + print "CUR: %r" % file_content + open("test.txt", "w").write(file_content) + dse.restore_snapshot(snapshot) + FILE_to_info.clear() + FILE_to_info_symb.clear() + + # Play the current file + try: + sb.run() + except FinnishOn as finnish_info: + print finnish_info.string + if finnish_info.string == "OK": + # Stop if the expected result is found + found = True + break + +# Assert that the result has been found +assert found == True +print "FOUND !" + +# Replay for real +print "Trying to launch the binary without Miasm" +crackme = subprocess.Popen([options.filename], stdout=subprocess.PIPE, + stderr=subprocess.PIPE) +stdout, stderr = crackme.communicate() +assert not stderr +stdout = stdout.strip() +print stdout +assert stdout == "OK" diff --git a/test/test_all.py b/test/test_all.py index 9b3f2dc1..633798f0 100755 --- a/test/test_all.py +++ b/test/test_all.py @@ -585,6 +585,17 @@ for options, nb_sol, tag in [([], 4, []), depends=[test_x86_32_if_reg], tags=tag) +dse_crackme_out = Example.get_sample("dse_crackme.c")[:-2] +dse_crackme = ExampleSymbolExec([Example.get_sample("dse_crackme.c"), + "-o", dse_crackme_out], + products=[dse_crackme_out], + executable="cc") +testset += dse_crackme +testset += ExampleSymbolExec(["dse_crackme.py", dse_crackme_out], + depends=[dse_crackme], + products=["test.txt"], + tags=[TAGS["z3"]]) + ## Jitter class ExampleJitter(Example): """Jitter examples specificities: |