Process Memory Layout

Virtual Memory Layout of a 32-bit Windows Process

When the Windows loader maps a PE file into memory, it arranges the sections into a virtual address space. Every 32-bit process gets a private 4 GB virtual address space, split between user mode (0x00000000-0x7FFFFFFF) and kernel mode (0x80000000-0xFFFFFFFF).

High address (0xFFFFFFFF)
┌─────────────────────────┐
│      Kernel Space        │  OS kernel — not accessible from user mode
├─────────────────────────┤  (0x80000000)
│         Stack            │  grows downward ↓
│                          │
│    (unallocated)         │
│                          │
│         Heap             │  grows upward ↑
├─────────────────────────┤
│    .bss / .data          │  Global variables
├─────────────────────────┤
│       .text              │  Executable code
├─────────────────────────┤
│      PE Headers          │
└─────────────────────────┘  (0x00400000 — typical ImageBase)
Low address

Refer to REMA eBook 2026, Figure 2.14 for the full virtual memory layout diagram with annotated address ranges.

The Stack

The stack is a LIFO (last-in, first-out) data structure managed automatically by the CPU.

• Grows downward: from high addresses toward low addresses
• PUSH decrements ESP by 4, then writes the value
• POP reads the value, then increments ESP by 4
• Stores: local variables, saved registers, return addresses, function arguments

Each function call creates a stack frame: a region of the stack holding the function's local variables, the saved EBP, and the return address. When the function returns, its frame is destroyed.

Stack frame layout (after prologue)

High address
┌─────────────────────────┐
│  Arg 2     [EBP+0x0C]   │  ← Passed by caller
│  Arg 1     [EBP+0x08]   │
│  Return Address [EBP+04]│  ← Where to resume after RET
│  Saved EBP [EBP+0x00]   │  ← EBP points here
│  Local var 1 [EBP-0x04] │  ← Current frame begins
│  Local var 2 [EBP-0x08] │
│  Buffer    [EBP-0x??]   │
└─────────────────────────┘  ← ESP points here
Low address

Why this matters for malware analysis

A buffer overflow on the stack writes past the buffer boundary upward: toward the saved EBP and then the return address. When RET executes, the CPU pops the corrupted value into EIP and jumps to attacker-controlled code.

Buffer at [EBP-0x40]
Overflow direction: low → high
Overwrites: local vars → saved EBP → return address

Recognising this layout in a debugger is the basis for understanding every stack exploitation technique.

The Heap

The heap is a pool of memory used for dynamic allocations requested at runtime.

• Grows upward: from low addresses toward high addresses
• malloc() / HeapAlloc(): requests heap memory
• free() / HeapFree(): releases heap memory
• VirtualAlloc(): large allocations with custom permissions

Malware and the heap

Malware frequently uses the heap to store unpacked payloads. If a binary calls VirtualAlloc with PAGE_EXECUTE_READWRITE, it is allocating a heap region where it can both write data and execute code: a strong indicator of runtime unpacking or shellcode injection.

push  PAGE_EXECUTE_READWRITE     ; flProtect = 0x40
push  MEM_COMMIT                 ; flAllocationType
push  payload_size               ; dwSize
push  0                          ; lpAddress (OS chooses)
call  VirtualAlloc               ; returns base address in EAX
; EAX now points to RWX memory — malware writes shellcode here

Stack vs Heap comparison

Property	Stack	Heap
Management	Automatic (CPU adjusts ESP)	Manual (programmer calls alloc/free)
Growth direction	Downward (high → low)	Upward (low → high)
Lifetime	Until function returns	Until explicitly freed
Speed	Fast (single SUB ESP)	Slower (heap manager search)
Typical abuse	Buffer overflow overwrites return address	Heap spray fills memory with shellcode

Loaded DLLs

In addition to the PE sections, a process's memory contains all loaded DLLs mapped into the same address space. In a debugger, the Modules panel (x64dbg: View → Modules) shows every DLL currently mapped.

Malware injected as a DLL appears here, but reflective DLL injection and some advanced techniques can hide from this list. The Volatility dlllist plugin (covered in Unit 5) detects discrepancies between the module list and actual memory mappings.

Interpreting Debugger Output

Understanding the memory layout transforms the register panel from noise into signal:

Register Value	Meaning
EIP in .text range	Normal code execution
EIP in heap range	Shellcode executing from heap: likely injection
ESP decreasing	Stack growing: function calls happening
EBP stable across loop	Loop executing within same frame
EAX = 0 after API call	API returned failure: check GetLastError

When EIP points outside .text or any known module, the process is executing injected code. This is the most direct indicator of code injection visible in a debugger.