!dr (hook access to debug registers)
Description of the '!dr' command in HyperDbg.
!dr
!dr [pid ProcessId (hex)] [core CoreId (hex)] [imm IsImmediate (yesno)] [buffer PreAllocatedBuffer (hex)] [script { Script (string) }] [condition { Condition (hex) }] [code { Code (hex) }]
Triggers, when the debugging machine accesses one of the hardware debug registers.
[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)
[script { Script (string) }] (optional)
[condition { Condition (hex) }] (optional)
[code { Code (hex) }] (optional)
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.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".
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
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.
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.
As EventType use
DEBUG_REGISTERS_ACCESSED in DEBUGGER_GENERAL_EVENT_DETAIL.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.
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