!interrupt (hook external device interrupts)

Description of '!interrupt' command in HyperDbg.

Command

!interrupt

Syntax

!interrupt [IDT Index (hex value)] [pid (hex value)] [core (hex value)] [imm (yes|no)] [event options]

Description

Triggers when the debugging machine encounters an external-interrupt. This command applies to only 32 to 255 entries of IDT (Interrupt Descriptor Table). If you need to hook entries between 0 to 31 of IDT, then you should use !exception instead.

When you enable this event, all entries from 32 to 255 will cause vm-exits, so this command will trigger on all external-interrupts; thus, making your computer substantially slower. This is not true about the !exception command as it will only trigger on that specific entry.

Parameters

[IDT Index (hex value)]

Trigger in the case of receiving an external-interrupt. The value should be between 0x20 to 0xff. If you don't specify this parameter, then it will be triggered for all external-interrupts.

[pid (hex value)]

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.

[core (hex value)]

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 (yes|no)]

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.

[event options]

Regular event parameters that are used in HyperDbg events. (For more information, read this topic)

Context

As the Context (r8 in custom code and rdx in condition code register) to the event trigger, HyperDbg sends vector or IDT index of the external-interrupt.

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

Imagine we want to break on entry 0x25 of IDT.

HyperDbg> !interrupt 0x25

If we want to break on external-interrupt (entry 0x25) from process id 0x490.

HyperDbg> !interrupt 0x25 pid 490

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> !interrupt 0x25 script { HyperDbg Script Here }

The above command when messages don't need to be delivered immediately.

HyperDbg> !interrupt 0x25 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> !interrupt 0x25 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 the occurrence of external-interrupts and run 3 nops whenever the event is triggered. Take a look at Run Custom Code for more information.

HyperDbg> !interrupt code {90 90 90}

Run Custom Code (Conditional)

Monitoring the external-interrupts occurrence and running 3 nops whenever the event condition is triggered and running 3 nops whenever the event is triggered. Take a look at Run Custom Code and how to create a condition for more information.

HyperDbg> !interrupt 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 EXTERNAL_INTERRUPT_OCCURRED and send the special entry between 0x20 to 0xff (if any) if you want to monitor just a special external-interrupt in OptionalParam1 in DEBUGGER_GENERAL_EVENT_DETAIL.

Please look at Remarks for more information.

Design

Take a look at "Design of !exception & !interrupt" to see how it works.

Remarks

You should avoid monitoring all external-interrupt because it is generally impossible. For example, thousands of clock-interrupts will be received, and if you want to handle all of them, it makes your system unresponsive. By the way, you can monitor just one external-interrupt without any problem.

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.

Requirements

None

!exception (hook first 32 entries of IDT)