Triggering Special Instructions
A description about hooking RDTSC, RDTSCP, I/O IN & OUT, RDPMC, etc.
There are special instructions in x86 and AMD64 processors that might be configured to cause vm-exits when executed; thus, we can intercept them.
For example, we might be interested in the execution of I/O instructions (IN & OUT). We can monitor memory-mapped I/O using the !monitor command, but for I/O mapped devices, we can use !ioin and !ioout commands.
Do not try to monitor all I/O ports or the I/O port for the serial device connected to the debugger if you are operating on Debugger Mode.
Using these commands, we can monitor I/O ports. For examples, let say we want to monitor the I/O port 0x3f8 for INinstruction.
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HyperDbg> !ioin 0x3f8
Copied!
If we want to monitor port 0x3f8 for OUT instruction, we use the following command.
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HyperDbg> !ioout 0x3f8
Copied!
Let's intercept another instruction.
We know that CPUID is an important instruction that tries to get processor features to see if a processor supports a special feature or not.
For example, we want to intercept all the CPUIDs that a process with process ID 0x490 tries to execute.
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HyperDbg> !cpuid pid 490
Copied!
You can also break on the execution of other instructions like:
  • RDTSC and RDTSCP using !tsc command
  • RDPMC using !pmc command
  • VMCALLs using !vmcall command
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