!vmcall (hook hypercalls)
Description of the '!vmcall' command in HyperDbg.
Command
!vmcall
Syntax
!vmcall [pid ProcessId (hex)] [core CoreId (hex)] [imm IsImmediate (yesno)] [sc EnableShortCircuiting (onoff)] [stage CallingStage (prepostall)] [buffer PreAllocatedBuffer (hex)] [script { Script (string) }] [asm condition { Condition (assembly/hex) }] [asm code { Code (assembly/hex) }] [output {OutputName (string)}]
Description
Triggers when the debugging machine executes VMCALL instruction.
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
.
[sc EnableShortCircuiting (onoff)] (optional)
[stage CallingStage (prepostall)] (optional)
[buffer PreAllocatedBuffer (hex)] (optional)
[script { Script (string) }] (optional)
[asm condition { Condition (assembly/hex) }] (optional)
[asm code { Code (assembly/hex) }] (optional)
[output {OutputName (string)}] (optional)
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.
Short-circuiting
Calling Stages
Debugger
This event supports three debugging mechanisms.
Break
Script
Custom Code
Break
We want to break and get control over all hypercalls (VMCALLs) execution in our system.
Imagine we want to break on all VMCALL executions of a process id 0x490 in core 2.
Script
The above command when messages don't need to be delivered immediately.
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
.
Custom Code
Run Custom Code (Unconditional)
Or if you want to use assembly codes directly, you can add an asm
before the code
.
Run Custom Code (Conditional)
Or if you want to use assembly codes directly, you can add an asm
before the condition
and also before the code
.
Keep in mind that a conditional event can be used in Breaking to Debugger and Running Script too.
IOCTL
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
Requirements
None
Related
None
Last updated