radare2/libr/anal/README

NOTE: Most of the information in this document is not matching with reality.
      Take it as random ideas, proposals and so on

Code analysis module
====================
* Opcodes that will be executed depending on cond?
  - for example: (x86, arm..) (0f94c2  setz dl)
* Direction of the stack? (inc/dec) required?
* Register value source type
  - This is static entropy level for a register at some point
  - Constant value
    mov eax, 33
    mov eax, [const] ; from ro memory
      static_entropy = 0;
  - Variable
    mov eax, [rwmem] ; from rw memory (variable)
      static_entropy = 1;
  - Modification
    add eax, ebx ; from rw memory (variable)
      static_entropy ++;

  * At any point of the program we can determine if a register
    has a static fixed value or the level of possible polimorfism

  -- store register values in execution traces

////////////////////////////////////////

Global picture

(anal) -> can keep track of results of different context (functions ...)
  |
  `---> we get a context.. so we work there with
       (anal context owns stack, regs, ...)
     - able to detect function arguments
     - we can configure the context in a way or other
     - it is able to get info from global anal
     - feeded with bytes

r_anal_get_bb(an, 0x804800);
r_anal_op_t * op = r_anal_get_op(an, 0x804800);
r_anal_get_fun(an, 0x804800);

----------------------------------------

// Must use r_alloc_pool for every type of structure (per function level)
// Must store all this info using r_db
// Only index when requested (tempral analysis are temporal)
// Memory selectors are just modifiers .. how?
// How to handle with self-modifying code?
  - if its a conditional branch, refs are true , false
    - if not and there is more than one branch is all the possibilities
  - if an address is accessed in read|write and exec mode we should warn!
  xrefs[] = {
    addr = 0x8048480
    type = R|W|X  - executable xrefs are control flow branches,
                  - read/write are for data
  }
  refs[] = {
    op   = eq,add,mul ??
    reg  = regidx
    addr = 0x8048580
    type = R|W|X
  }

// we need an api in r_buf to modify bits with endian and values..
struct bin {
  int offset;
  int size;
  int endian;
};

enum type {
  IMM
  REG
  MEM
};

struct r_anal_value_t {
  int op; // NOP, ADD, SEL, ...
  int type; // opcode, reg, imm, addr
  ut64 num; // idxofreg, immvalue, addrnum
  struct bin bin;
  int size;
  int nextop; // ADD, MUL, ...
  struct r_anal_value_t *next;
};

struct arg {
  int rw; // READ | WRITE direction
  int nv; // number of values
  struct r_anal_value_t *v;
};

mov eax, [0x8048+eax*4]

  mov -> args = { "eax", {0x8048 {+eax*4}} }

struct r_anal_ref_t {
  int type; // READ, WRITE, EXEC
  struct r_anal_value_t value;
};

struct r_anal_op_t {
  ut64 addr;
  int frame;
  int type;
  int cond;
  int nestlevel;
  int length;
  int crc;
  struct r_anal_value_t rep;
  int nargs;
  struct arg args[];

  struct r_anal_op_t *next;
  int nrefs;
  struct r_anal_ref_t refs[];
  int nxrefs;
  struct r_anal_ref_t xrefs[];
};

/* basic block */
struct r_anal_bb_t {
  ut64 addr;
  int type;
  int size;
  ut8 *bytes;
  struct r_anal_op_t *head; // opcode heading this basic block
  struct r_anal_ref_t refs[];
  struct r_anal_ref_t xrefs[];
};

/* function */
struct r_anal_fun_t {
  char *name;
  ut64 addr;
  int size;
  // XXX: use r_ranges instead of addr+size?
  struct r_anal_ref_t refs[];
  struct r_anal_ref_t xrefs[];
};

/* used to emulate */
struct r_anal_arch_t {
  struct r_reg_t reg;
  char **regs;
  int pc; // program counter
  int sp; // stack pointer
  int bp; // base pointer
  int gp; // global pointer
  int sr; // src
  int dr; // dst
};

const char **regs = { "eax", "ebx", "ecx", "...", NULL };

  if (opcode.xrefs[i].type & R_ANAL_XS_EXEC)

// compilation process defines a mapping between the binary representation
// of an opcode into an AST of structs describing the opcode itself or
// we can just serialize it into a evaluable string
// - evaluable strings are cheaper in memory consumption
// - strstr(es, "%eax") easy way to check if a register is used
// - the eval string should be converted into an AST at some point

Analysis levels:
================
- opcode level
  - frame size
  - conditional (used by branches(jumps) and arm opcodes)
  - weight (importance) (if <0, it is a nop) trash detection
  - XXX file/line (dwarf nfo??? here) i think no
  - lifetime of register value (detect if
  - nesting level (branch analysis)
  - sign
  - type
  -- operand level:
     - bitsize
     - mem | reg | imm
       - value
     - direction (read|write)
     - operand index
- basic block level
  - bytes + length + (checksum?)
  - type (head, tail, body, last)
  - xrefs (branches to here)
  - refs (must be an array)
    - true branch
    - false branch
    - destinations[] // for call eax and so
- function level
  - name
  - offset range (r_range here, functions do not need to be linear)
  - variables (use r_var) (( merge r_var here? ))
  - arguments ("")
  - xrefs
  - calls (outrefs)
  == graph simplification (serialize blocks with direct branches (jmp))
- program
  - comprends data + code trees
  - all references must be stored twice
  - r_range of functions, data and other shit

Context analysis:
=================
- Merge r_vm here -- multiarchitecture code emulation
- Allows to track register lifetime,
- Detect possible values for 'call eax' f.ex
- Identify fake conditional branches

TEH RIR
=======
The radare intermediate representation.
 - ascii representation of opcode level analysis

-- epilog/prolog bytez for extra function detection

Architecture language
=====================
Allows to describe an architecture (byte parsing, read/write)
 - opcode reassembling
 - automatic code analysis
 r_anal_opcode_set(op, R_OPTYPE_ADD);
 - opcode level analysis can be manually modified in runtime
   - basic blocks can change

Decompilation
=============
Use ALT .. in a inverse way OMG thats freaking

/////////////////////////////////////////////////////////////

opcode_analyze ()
  - parse bytes and fill an structure
  - opcode type and arguments
  - underlying vm code
opcode_modify ()
  - modify the bytes based on the structure changes
  - the structure should expose the bit level info to make this possible
   // this is //
   * modify reg, immediate or memory values

+--------------+
| AnalArchLang | **
+--------------+
if [arg0 == 0xff] {
	reg = { eax, ecx, edx, ebx, esp, ebp, esi, edi }
	jmp [0xe0+reg]
	jmp [0xe8+reg]

	reg = { eax, ecx, edx, ebx, esp, ebp, esi, edi }
	push [0xf0+reg]

	reg = { eax, ecx, edx, ebx, esp, ebp, esi, edi }
	call [0xd0+reg]
	call [0xd8+reg]
}

[0:7]=e8 {
  type = "call"
  addr = [8:31]
  len = 5
}
[0:7]=50 && [0:7]<60 {
  type = "push"
  len = 1
}
[0:7]=c3 {
  type = "ret"
  len = 1
}

BASIC OPS we need for the IR
============================ -- this is RISC! :D

Each opcode must support a size value. The format is:
We need some intermediate temporal registers


lispy assembly:
  (addi eax 3)
  (addi *(+ eax 8) 3)

  lea edi, [ecx*4-0x4]
  (set edi (- (* ecx 4) 4)
  (set edi (* ecx 4 - 4)) ; iterative format

     1 byte       1           N       N
  [ opcode ] [ type|size ] [ arg ] [ arg ]

type = [ op | reg | mem | imm ]  ; 2 bits is enought
size = 1, 2, 4, 8           ; byte level

ADD reg, reg
SUB reg, 
JMP reg
JMP imm
JMP mem
SET reg, imm
STO mem, reg   ; store register value into memory
LOA reg, mem   ; load memory value into register
 ...