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!dr (hook access to debug registers)

Description of the '!dr' command in HyperDbg.

Command

!dr

Syntax

!dr [pid ProcessId (hex)] [core CoreId (hex)] [imm IsImmediate (yesno)] [buffer PreAllocatedBuffer (hex)] [script { Script (string) }] [condition { Condition (hex) }] [code { Code (hex) }]

Description

Triggers, when the debugging machine accesses one of the hardware debug registers.

Parameters

[pid ProcessId (hex)] (optional)
Optional value to trigger the event in just a specific process. Add pid xx to your command; thus, the command will be executed if the process id is equal to xx. If you don't specify this option, then by default, you receive events on all processes.
Still, in the case of user-mode debugging, HyperDbg will apply it only to the current active debugging process (not all the processes). In that case, you can specify pid all to intercept events from the entire system.
[core CoreId (hex)] (optional)
Optional value to trigger the event in just a specific core. Add core xx to your command thus command will be executed if core id is equal to xx. If you don't specify this option, then by default, you receive events on all cores.
[imm IsImmediate (yesno)] (optional)
Optional value in which yes means the results (printed texts in scripts) should be delivered immediately to the debugger. no means that the results can be accumulated and delivered as a couple of messages when the buffer is full; thus, it's substantially faster, but it's not real-time. By default, this value is set to yes.
[buffer PreAllocatedBuffer (hex)] (optional)
Optional value which reserves a safe pre-allocated buffer to be accessed within the event codes.
[script { Script (string) }] (optional)
A HyperDbg script will be executed each time the event is triggered.
[condition { Condition (hex) }] (optional)
Optional hex assembly codes which check for conditions in assembly.
[code { Code (hex) }] (optional)
Optional hex assembly codes will be executed each time the event is triggered.

Context

As the Context ($context pseudo-register in the event's script, r8 in custom code, and rdx in condition code register) to the event trigger, HyperDbg sends NULL.

Debugger

This event supports three debugging mechanisms.
  • Break
  • Script
  • Custom Code
Please read "How to create a condition?" if you need a conditional event, a conditional event can be used in all "Break", "Script", and "Custom Code".

Break

We want to break and get control over each access to hardware debug registers in our system.
HyperDbg> !dr
Imagine we want to break on all accesses to hardware debug registers of a process id 0x490.
HyperDbg> !dr pid 490
Imagine we want to break on all accesses to hardware debug registers of a process id 0x490 and only on core 3.
HyperDbg> !dr pid 490 core 3

Script

Using the following command, you can use HyperDbg's Script Engine. You should replace the string between braces (HyperDbg Script Here) with your script. You can find script examples here.
HyperDbg> !dr script { HyperDbg Script Here }
The above command when messages don't need to be delivered immediately.
HyperDbg> !dr script { HyperDbg Script Here } imm no
Script (From File)
If you saved your script into a file then you can add file: instead of a script and append the file path to it. For example, the following examples show how you can run a script from file:c:\users\sina\desktop\script.txt.
HyperDbg> !dr script {file:c:\users\sina\desktop\script.txt}
You can use event forwarding to forward the event monitoring results from this event and other events to an external source, e.g., File, NamedPipe, or TCP Socket. This way, you can use HyperDbg as a monitoring tool and gather your target system's behavior and use it later or analyze it on other systems.

Custom Code

Please read "How to create an action?" to get an idea about how to run the custom buffer code in HyperDbg.
Your custom code will be executed in vmx-root mode. Take a look at this topic for more information. Running code in vmx-root is considered "unsafe".
Run Custom Code (Unconditional)
Monitoring process ID 0x490 for any access to hardware debug registers and run 3 nops whenever the event is triggered. Take a look at Run Custom Code for more information.
HyperDbg> !dr pid 490 code {90 90 90}
Run Custom Code (Conditional)
Monitoring process ID 0x490 for any access to hardware debug registers and run 3 nops whenever the event condition is triggered and run 3 nops whenever the event is triggered. Take a look at Run Custom Code and how to create a condition for more information.
HyperDbg> !dr pid 490 code {90 90 90} condition {90 90 90}
Keep in mind that a conditional event can be used in Breaking to Debugger and Running Script too.

IOCTL

This command uses the same method to send IOCTL for regular events.
As EventType use DEBUG_REGISTERS_ACCESSED in DEBUGGER_GENERAL_EVENT_DETAIL.

Design

This command uses Debug Register Access (EXIT_REASON_DR_ACCESS) vm-exits (29) to implement hardware debug registers hooks.
This is an event command, but in the current version of HyperDbg (in Debugger Mode), this command will continue the debuggee for some time; however, you can use this trick to make sure you won't lose any event.

Remarks

None

Requirements

None
None