!sysret, !sysret2 (hook SYSRET instruction execution)
Description of '!sysret, !sysret2' commands in HyperDbg.
!sysret!sysret2
!sysret [pid ProcessId (hex)] [core CoreId (hex)] [imm IsImmediate (yesno)] [sc EnableShortCircuiting (onoff)] [stage CallingStage (prepostall)] [buffer PreAllocatedBuffer (hex)] [script { Script (string) }] [condition { Condition (hex) }] [code { Code (hex) }]!sysret2 [pid ProcessId (hex)] [core CoreId (hex)] [imm IsImmediate (yesno)] [sc EnableShortCircuiting (onoff)] [stage CallingStage (prepostall)] [buffer PreAllocatedBuffer (hex)] [script { Script (string) }] [condition { Condition (hex) }] [code { Code (hex) }]
Triggers when the debugging machine executes a sysret instruction or, in other words, when Windows tries to return to user-mode from a previous syscall.
When you enable this event, all sysret instructions from all processes will be monitored, and due to the limitation in hardware, you can't expect it to trigger for just one process. Still, you can configure the debugger to trigger the event for you in the case of a special process by adding
pid xxto the command.The difference between !sysret and !sysret2 is that we safely check the memory in the first command to see if the instruction that caused #UD is really an SYSRET or a SYSCALL. So, we access the memory in this command. However, we realized that older systems have problems with this way of memory access. In the second command, we just check for the RIP to see if it's a kernel address or a user address. Usually, this method works without error for several hours, but if one application generates a #UD, then a BSOD will happen. The second method is generally faster in speed, but we encourage you to use the first command and if your computer doesn't support the first command, then use the second command.
[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)
Optional value to ignore the emulation (skip execution) of the event. Add
sc on to your command thus whenever the event is triggered, the effects and the execution of the actual event will be ignored. For more information, please read this article. If you don't specify this option, then by default, all the events will be emulated (executed). By default, this value is set to off.[stage CallingStage (prepostall)] (optional)
Optional value to configure the calling stage of the event. To trigger the event before the emulation, include
stage pre in your command. Conversely, using stage post will cause the event to be triggered after the emulation. Additionally, using stage all will trigger the event both before and after the emulation. For more information, please read this article. By default, this value is set to pre.[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 the rip register of where executes the sysret instruction. Generally, it should be the same in value in Windows (just one sysret instruction is in Windows).This event supports 'event short-circuiting', which means that you can configure HyperDbg to ignore its execution and its effects. For additional details, please refer to the article provided here.
This event supports different calling stages. The 'pre' calling stage is triggered prior to the user transfer, whereas the 'post' calling stage is triggered subsequent to the user transfer. In addition, the 'all' calling stage will trigger the event in both cases. You can ignore the event in the 'pre' stage. For more information, please refer to the article provided here.
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".
You can use condition if you want to check the sysret parameters, for example, you can check the result of a previous syscall which now wants to return to user-mode by executing sysret instruction to see if it matches to your debugging logic or not and have a conditional sysret hooker and also you can change the parameters of a sysret.
Imagine we want to break on all sysret executions of a process id 0x490.
HyperDbg> !sysret pid 490
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> !sysret script { HyperDbg Script Here }
The above command when messages don't need to be delivered immediately.
HyperDbg> !sysret 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> !sysret 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 sysret instruction execution and run 3 nops whenever the event is triggered. Take a look at Run Custom Code for more information.
HyperDbg> !sysret pid 490 code {90 90 90}
Run Custom Code (Conditional)
Monitoring process ID 0x490 for sysret instruction execution 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> !sysret 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
SYSCALL_HOOK_EFER_SYSRET in DEBUGGER_GENERAL_EVENT_DETAIL.This command is not PatchGurad compatible, which means that PatchGuard detects this command and will cause BSOD; thus, make sure to turn it off (e.g., attaching a kernel-mode WinDbg debugger at the start of the Windows) before using this command. Disabling Driver Signature Enforcement alone won't turn off the PatchGuard.
This command makes your computer substantially slower.
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.
Post-Nehalem Processor (EPT)