!vmcall (hook hypercalls)

Command
!vmcall
Syntax
!vmcall [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 executes VMCALL instruction.
By using this command, you also receive HyperDbg's hypercalls. You shouldn't modify them.
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 all hypercalls (VMCALLs) execution in our system.
1
HyperDbg> !vmcall
Copied!
Imagine we want to break on all VMCALL executions of a process id 0x490 in core 2.
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HyperDbg> !vmcall pid 490 core 2
Copied!
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.
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HyperDbg> !vmcall script { HyperDbg Script Here }
Copied!
The above command when messages don't need to be delivered immediately.
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HyperDbg> !vmcall script { HyperDbg Script Here } imm no
Copied!
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.
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HyperDbg> !vmcall script {file:c:\users\sina\desktop\script.txt}
Copied!
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 VMCALL instruction execution and run 3 nops whenever the event is triggered. Take a look at Run Custom Code for more information.
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HyperDbg> !vmcall pid 490 code {90 90 90}
Copied!
Run Custom Code (Conditional)
Monitoring process id 0x490 for VMCALL instruction execution and run 3 nops whenever the event condition is triggered and runs 3 nops whenever the event is triggered. Take a look at Run Custom Code and how to create a condition for more information.
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HyperDbg> !vmcall pid 490 code {90 90 90} condition {90 90 90}
Copied!
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 VMCALL_INSTRUCTION_EXECUTION in DEBUGGER_GENERAL_EVENT_DETAIL.
Design
This command uses VMCALL (EXIT_REASON_VMCALL - 18) vm-exit to implement hypercall hooks.
Remarks
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
Related
None

!pmc (hook RDPMC instruction execution)

!exception (hook first 32 entries of IDT)

Last modified 29d ago

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