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"""
This example demonstrates the recovering of possible C types for an arbitrary
variable in an assembly code (the types are inferred from the function
argument types). It also displays the C code used to access this variable.
Input:
* definitions of the C types that can be used by the code
* layout of structures (packed/not packed)
* prototype of the analyzed function
Algorithm:
The DepGraph of the target variable is computed, which gives possible
expressions for this variable. For each DepGraph solution, if the expression
depends on typed arguments, the code infers the variable type and displays the C
code to access this variable.
Here be dragons:
For the moment, Miasm can infer C types (and generate C) for simple expressions.
To summarize, Miasm only supports accesses that do not involve arithmetic or
conditional expressions such as the following:
* var1.field
* var1[12][4]
* *(var1.field->tab[4])
Unsupported forms:
* var1 + var2
* var1[var2+4]
* var1?var2->field:6
In the following example, we have an explicit cast for "age", from uint16_t to
uint64_t, and for "height", from uint32_t to uint64_t. We are adding a naive
reduction rule to support such a cast.
First, in the type inference engine:
ExprCompose(int, 0) => int
Then, in the C generator:
ExprCompose(var1, 0) => var1
"""
import sys
from miasm2.analysis.machine import Machine
from miasm2.analysis.binary import Container
from miasm2.expression.expression import ExprOp, ExprCompose, ExprId, ExprInt
from miasm2.analysis.depgraph import DependencyGraph
from miasm2.arch.x86.ctype import CTypeAMD64_unk
from miasm2.core.objc import ExprToAccessC, CHandler
from miasm2.core.objc import CTypesManagerNotPacked
from miasm2.core.ctypesmngr import CAstTypes, CTypePtr, CTypeStruct
def find_call(ira):
"""Returns (irb, index) which call"""
for irb in ira.blocks.values():
out = set()
if len(irb.irs) < 2:
continue
assignblk = irb.irs[-2]
for src in assignblk.itervalues():
if not isinstance(src, ExprOp):
continue
if not src.op.startswith('call_func'):
continue
out.add((irb, len(irb.irs) - 2))
if len(out) != 1:
continue
irb, index = out.pop()
yield irb, index
class MyExprToAccessC(ExprToAccessC):
"""Custom ExprToAccessC to complete expression traduction to C"""
def reduce_compose(self, node, **kwargs):
"""Custom reduction rule: {XXX, 0} -> XXX"""
if not (isinstance(node.expr, ExprCompose) and
len(node.expr.args) == 2 and
node.expr.args[1].is_int(0)):
return None
found = []
for subcgenobj in node.args[0].info:
found.append(subcgenobj)
return found
reduction_rules = ExprToAccessC.reduction_rules + [reduce_compose]
def get_funcs_arg0(ctx, ira, lbl_head):
"""Compute DependencyGraph on the func @lbl_head"""
g_dep = DependencyGraph(ira, follow_call=False)
element = ira.arch.regs.RSI
for irb, index in find_call(ira):
instr = irb.irs[index].instr
print 'Analysing references from:', hex(instr.offset), instr
g_list = g_dep.get(irb.label, set([element]), index, set([lbl_head]))
for dep in g_list:
emul_result = dep.emul(ctx)
value = emul_result[element]
yield value
class MyCHandler(CHandler):
"""Custom CHandler to add complementary C handling rules"""
exprToAccessC_cls = MyExprToAccessC
data = open(sys.argv[1]).read()
# Digest C informations
text = """
struct human {
unsigned short age;
unsigned int height;
char name[50];
};
struct ll_human {
struct ll_human* next;
struct human human;
};
"""
base_types = CTypeAMD64_unk()
types_ast = CAstTypes()
types_ast.add_c_decl(text)
types_mngr = CTypesManagerNotPacked(types_ast, base_types)
# Analyze binary
cont = Container.fallback_container(data, None, addr=0)
machine = Machine("x86_64")
dis_engine, ira = machine.dis_engine, machine.ira
mdis = dis_engine(cont.bin_stream, symbol_pool=cont.symbol_pool)
addr_head = 0
blocks = mdis.dis_multiblock(addr_head)
lbl_head = mdis.symbol_pool.getby_offset(addr_head)
ir_arch_a = ira(mdis.symbol_pool)
for block in blocks:
ir_arch_a.add_block(block)
open('graph_irflow.dot', 'w').write(ir_arch_a.graph.dot())
# Main function's first argument's type is "struct ll_human*"
ptr_llhuman = types_mngr.get_objc(CTypePtr(CTypeStruct('ll_human')))
arg0 = ExprId('ptr', 64)
ctx = {ir_arch_a.arch.regs.RDI: arg0}
expr_types = {arg0: (ptr_llhuman,),
ExprInt(0x8A, 64): (ptr_llhuman,)}
mychandler = MyCHandler(types_mngr, expr_types)
for expr in get_funcs_arg0(ctx, ir_arch_a, lbl_head):
print "Access:", expr
for c_str, ctype in mychandler.expr_to_c_and_types(expr):
print '\taccess:', c_str
print '\tc type:', ctype
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