HyperDbg Documentation
CommunityDownloadResearchTutorialhwdbg
  • HyperDbg
  • Getting Started
    • Quick Start
    • FAQ
    • Build & Install
    • Attach to HyperDbg
      • Attach to a remote machine
      • Attach to local machine
      • Start a new process
      • Attach to a running process
  • Using HyperDbg
    • Prerequisites
      • Operation Modes
      • How to create a condition?
      • How to create an action?
      • Signatures
    • User-mode Debugging
      • Principles
      • Examples
        • basics
        • events
          • Getting Results of a System-call
    • Kernel-mode Debugging
      • Principles
      • Examples
        • beginning
          • Connecting To HyperDbg
          • Configuring Symbol Server/Path
        • basics
          • Setting Breakpoints & Stepping Instructions
          • Displaying & Editing & Searching Memory
          • Showing & Modifying Registers and Flags
          • Switching to a Specific Process or Thread
          • Mapping Data & Create Structures, and Enums From Symbols
        • events
          • Managing Events
          • Hooking Any Function
          • Intercepting All SYSCALLs
          • Monitoring Accesses To Structures
          • Triggering Special Instructions
          • Identifying System Behavior
        • Scripting Language Examples
    • Software Development Kit (SDK)
      • Events
        • Conditions
        • Actions
      • IOCTL
        • Event Registration
  • Commands
    • Debugging Commands
      • ? (evaluate and execute expressions and scripts in debuggee)
      • ~ (display and change the current operating core)
      • a (assemble virtual address)
      • load (load the kernel modules)
      • unload (unload the kernel modules)
      • status (show the debuggee status)
      • events (show and modify active/disabled events)
      • p (step-over)
      • t (step-in)
      • i (instrumentation step-in)
      • gu (step-out or go up)
      • r (read or modify registers)
      • bp (set breakpoint)
      • bl (list breakpoints)
      • be (enable breakpoints)
      • bd (disable breakpoints)
      • bc (clear and remove breakpoints)
      • g (continue debuggee or processing kernel packets)
      • x (examine symbols and find functions and variables address)
      • db, dc, dd, dq (read virtual memory)
      • eb, ed, eq (edit virtual memory)
      • sb, sd, sq (search virtual memory)
      • u, u64, u2, u32 (disassemble virtual address)
      • k, kd, kq (display stack backtrace)
      • dt (display and map virtual memory to structures)
      • struct (make structures, enums, data types from symbols)
      • sleep (wait for specific time in the .script command)
      • pause (break to the debugger and pause processing kernel packets)
      • print (evaluate and print expression in debuggee)
      • lm (view loaded modules)
      • cpu (check cpu supported technologies)
      • rdmsr (read model-specific register)
      • wrmsr (write model-specific register)
      • flush (remove pending kernel buffers and messages)
      • prealloc (reserve pre-allocated pools)
      • preactivate (pre-activate special functionalities)
      • output (create output source for event forwarding)
      • test (test functionalities)
      • settings (configures different options and preferences)
      • exit (exit from the debugger)
    • Meta Commands
      • .help (show the help of commands)
      • .debug (prepare and connect to debugger)
      • .connect (connect to a session)
      • .disconnect (disconnect from a session)
      • .listen (listen on a port and wait for the debugger to connect)
      • .status (show the debugger status)
      • .start (start a new process)
      • .restart (restart the process)
      • .attach (attach to a process)
      • .detach (detach from the process)
      • .switch (show the list and switch between active debugging processes)
      • .kill (terminate the process)
      • .process, .process2 (show the current process and switch to another process)
      • .thread, .thread2 (show the current thread and switch to another thread)
      • .pagein (bring the page into the RAM)
      • .dump (save the virtual memory into a file)
      • .formats (show number formats)
      • .script (run batch script commands)
      • .sympath (set the symbol server)
      • .sym (load pdb symbols)
      • .pe (parse PE file)
      • .logopen (open log file)
      • .logclose (close log file)
      • .cls (clear the screen)
    • Extension Commands
      • !a (assemble physical address)
      • !pte (display page-level address and entries)
      • !db, !dc, !dd, !dq (read physical memory)
      • !eb, !ed, !eq (edit physical memory)
      • !sb, !sd, !sq (search physical memory)
      • !u, !u64, !u2, !u32 (disassemble physical address)
      • !dt (display and map physical memory to structures)
      • !track (track and map function calls and returns to the symbols)
      • !epthook (hidden hook with EPT - stealth breakpoints)
      • !epthook2 (hidden hook with EPT - detours)
      • !monitor (monitor read/write/execute to a range of memory)
      • !syscall, !syscall2 (hook system-calls)
      • !sysret, !sysret2 (hook SYSRET instruction execution)
      • !mode (detect kernel-to-user and user-to-kernel transitions)
      • !cpuid (hook CPUID instruction execution)
      • !msrread (hook RDMSR instruction execution)
      • !msrwrite (hook WRMSR instruction execution)
      • !tsc (hook RDTSC/RDTSCP instruction execution)
      • !pmc (hook RDPMC instruction execution)
      • !vmcall (hook hypercalls)
      • !exception (hook first 32 entries of IDT)
      • !interrupt (hook external device interrupts)
      • !dr (hook access to debug registers)
      • !ioin (hook IN instruction execution)
      • !ioout (hook OUT instruction execution)
      • !hide (enable transparent-mode)
      • !unhide (disable transparent-mode)
      • !measure (measuring and providing details for transparent-mode)
      • !va2pa (convert a virtual address to physical address)
      • !pa2va (convert physical address to virtual address)
      • !dump (save the physical memory into a file)
      • !pcitree (show PCI/PCIe device tree)
      • !pcicam (dump the PCI/PCIe configuration space)
      • !idt (show Interrupt Descriptor Table entries)
      • !apic (dump local APIC entries in XAPIC and X2APIC modes)
      • !ioapic (dump I/O APIC)
    • Scripting Language
      • Assumptions & Evaluations
      • Variables & Assignments
      • Casting & Type-awareness
      • Conditionals & Loops
      • Constants & Functions
      • Debugger Script (DS)
      • Examples
        • view system state (registers, memory, variables)
        • change system state (registers, memory, variables)
        • trace function calls
        • pause the debugger conditionally
        • conditional breakpoints and events
        • patch the normal sequence of execution
        • access to a shared variable from different cores
        • count occurrences of events
      • Functions
        • debugger
          • pause
        • events
          • event_enable
          • event_disable
          • event_clear
          • event_sc
          • event_inject
          • event_inject_error_code
          • flush
        • exports
          • print
          • printf
        • interlocked
          • interlocked_compare_exchange
          • interlocked_decrement
          • interlocked_exchange
          • interlocked_exchange_add
          • interlocked_increment
        • memory
          • check_address
          • eb, ed, eq
          • eb_pa, ed_pa, eq_pa
          • memcpy
          • memcpy_pa
          • memcmp
          • virtual_to_physical
          • physical_to_virtual
        • diassembler
          • disassemble_len
          • disassemble_len32
        • spinlocks
          • spinlock_lock
          • spinlock_lock_custom_wait
          • spinlock_unlock
        • strings
          • strlen
          • wcslen
          • strcmp
          • strncmp
          • wcscmp
          • wcsncmp
    • Commands Map
  • Tips & Tricks
    • Considerations
      • Basic concepts in Intel VT-x
      • VMX root-mode vs VMX non-root mode
      • The "unsafe" behavior
      • Script engine in VMX non-root mode
      • Difference between process and thread switching commands
      • Accessing Invalid Address
      • Transparent Mode
    • Nested-Virtualization Environments
      • Supported Virtual Machines
      • Run HyperDbg on VMware
      • Run HyperDbg on Hyper-V
      • Supporting VMware/Hyper-V
      • VMware backdoor I/O ports
    • Misc
      • Event forwarding
      • Event short-circuiting
      • Event calling stage
      • Instant events
      • Message overflow
      • Customize build
        • Increase Communication Buffer Size
        • Number of EPT Hooks in One Page
        • Change Script Engine Limitations
      • Enable and disable events in Debugger Mode
      • Switch to New Process Layout
  • Contribution
    • Style Guide
      • Coding style
      • Command style
      • Doxygen style
    • Logo & Artworks
  • Design
    • Features
      • VMM (Module)
        • Control over NMIs
        • VMX root-mode compatible message tracing
        • Design of !epthook
        • Design of !epthook2
        • Design of !monitor
        • Design of !syscall & !sysret
        • Design of !exception & !interrupt
    • Debugger Internals
      • Events
      • Conditions
      • Actions
      • Kernel Debugger
        • Design Perspective
        • Connection
  • Links
    • Twitter
    • Telegram
    • Discord
    • Matrix
    • Mastodon
    • YouTube
    • hwdbg (Chip Debugger)
    • Doxygen
    • Contribution
Powered by GitBook
On this page
  • Access invalid address from VMI Mode
  • Access invalid address from Debugger Mode
Edit on GitHub
  1. Tips & Tricks
  2. Considerations

Accessing Invalid Address

Considerations for accessing memory in different modes

PreviousDifference between process and thread switching commandsNextTransparent Mode

Last updated 6 months ago

Accessing memory could be challenging depending on the fact that HyperDbg tries to access memory from VMX-root mode. Generally, if you see the following error in HyperDbg, this page is to help you fix this problem.

err, invalid address (c0000005)
address may be paged-out or unavailable on the page table due to 'demand paging'
please refer to https://docs.hyperdbg.org/tips-and-tricks/considerations/accessing-invalid-address for further information

As the code implies, HyperDbg couldn't determine whether the address is valid or invalid. It typically happens when the address may be paged out or unavailable on the page table due to '' and since HyperDbg could not perform paging in the VMX-root mode, it throws this error.

Thus, two situations might happen here.

First, the address is invalid!

If the address is not valid and not allocated by OS, surely you cannot put a hook on it or view its content.

Second, the address is actually valid but still, we get this error.

Some addresses might not be available on the RAM (paged out by the operating system) or the operating system did not allocate a physical memory for the address as it brings the page into the RAM only when an attempt is made to access it.

Another scenario is that the page is already in the RAM but from the current view of the process (based on the current CR3 register), it is not present in the page-table. For example, the address might be located in the 'kernel32' or 'ntdll' memory but since the current process never accessed some of the functions (pages) it is not present based on their paging base of the memory.

In the second scenario, you have two options forcing the operating system to bring the page into the memory or make it present in both and the .

Access invalid address from VMI Mode

In this mode, virtual memory reading commands like or assembler commands like , all access the memory from VMX non-root mode. This means that accessing the memory will trigger a page-fault and if the address is actually valid, the OS either brings it to the RAM or makes it present to the process.

For example, assume that we want to apply the following EPT hook (e.g., by using the '').

HyperDbg> !epthook kernel32!LoadLibraryW script {
> printf("LoadLibrary called!\n"); 
> }
err, invalid address (c0000005)
address may be paged-out or unavailable on the page table due to 'demand paging'
please refer to https://docs.hyperdbg.org/tips-and-tricks/considerations/accessing-invalid-address for further information

If you access this function directly using the memory access commands or assembler commands,

HyperDbg> u kernel32!LoadLibraryW

or

yperDbg> u kernel32!LoadLibraryW pid 1c0

Then when you run your EPT hook again, the address is valid this time!

HyperDbg> !epthook kernel32!LoadLibraryW script {
> printf("LoadLibrary called!\n"); 
> }
LoadLibrary called!
LoadLibrary called!
LoadLibrary called!
LoadLibrary called!
...

Access invalid address from Debugger Mode

0: kHyperDbg> !epthook kernel32!LoadLibraryW script {
> printf("LoadLibrary called!\n"); 
> }
err, invalid address (c0000005)
address may be paged-out or unavailable on the page table due to 'demand paging'
please refer to https://docs.hyperdbg.org/tips-and-tricks/considerations/accessing-invalid-address for further information

In order to bring it to the memory, run the following command:

0: kHyperDbg> .pagein kernel32!LoadLibraryW
the page-fault is delivered to the target thread
press 'g' to continue debuggee (the current thread will execute ONLY one instruction and will be halted again)...

0: kHyperDbg> g
0: kHyperDbg> !epthook kernel32!LoadLibraryW script {
> printf("LoadLibrary called!\n"); 
> }

0: kHyperDbg> g
LoadLibrary called!
LoadLibrary called!
LoadLibrary called!
LoadLibrary called!
...

Please remember that these techniques only apply when the address is actually valid, if the address is not allocated and invalid, then it does not make sense to access them!

If you are in the debugger mode, the debuggee cannot switch between processes. At this point, you can use the '' command to inject a page-fault (#PF) and force the operating system to bring the page into the memory or make it present in the paging tables of the current process.

Once you run the '' command the OS finds a chance to bring the page into the memory or make it present in the memory and it immediately pauses the debuggee again, then you can apply your EPT hook.

Please note that technically, you could use the '' command on a large range of memory. However, in large memory ranges, there are often page entries that are already valid (paged in or never paged out by the OS). In those cases, if you bring them into memory (force the OS to page them in) using the '' command, it will disrupt the OS semantics. This command injects a #PF (page fault) into the OS, and if the address is already valid, the operating system does not expect to receive a page fault for an available page, which might or will cause a triple fault and consequently a system restart or crash.

demand paging
VMI Mode
Debugger Mode
db, dc, dd, and dq
u, and u2
!epthook
.pagein
g
.pagein
.pagein