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rdmsr.md

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Description of the 'rdmsr' command in HyperDbg.

rdmsr (read model-specific register)

Command

rdmsr

Syntax

rdmsr [Msr (hex)] [core CoreNumber (hex)]

Description

Reads the model-specific register using 'rdmsr' instruction.

Parameters

[Msr (hex)]

The index of MSR (ECX Register for 'rdmsr' instruction).

[core CoreNumber (hex)] (optional)

The core that we want to read the 'rdmsr' from it.

{% hint style="success" %} If you don't specify the 'core' by default, it shows the MSR for all cores. {% endhint %}

Examples

The following command shows the MSR register for c0000082 using rdmsr command.

HyperDbg> rdmsr c0000082
core : 0x0 - msr[c0000082] = fffff807`73553180
core : 0x1 - msr[c0000082] = fffff807`73553180
core : 0x2 - msr[c0000082] = fffff807`73553180
core : 0x3 - msr[c0000082] = fffff807`73553180

The following example shows the MSR c0000082 for core 2.

HyperDbg> rdmsr c0000082 core 2
core : 0x2 - msr[c0000082] = fffff807`73553180

IOCTL

This function works by calling DeviceIoControl with IOCTL = IOCTL_DEBUGGER_READ_OR_WRITE_MSR, you have to send it in the following structure.

typedef struct _DEBUGGER_READ_AND_WRITE_ON_MSR {

  UINT64 Msr; // It's actually a 32-Bit value but let's not mess with a register
  UINT32 CoreNumber; // specifies the core to execute wrmsr or read the msr
                     // (DEBUGGER_READ_AND_WRITE_ON_MSR_APPLY_ALL_CORES mean all the cores)
  DEBUGGER_MSR_ACTION_TYPE
  ActionType; // Detects whether user needs wrmsr or rdmsr
  UINT64 Value;

} DEBUGGER_READ_AND_WRITE_ON_MSR, *PDEBUGGER_READ_AND_WRITE_ON_MSR;

Where Msr is ecx value for 'rdmsr' or 'wrmsr' instruction, CoreNumber is the target core that you want to read or write on it and ActionType shows whether it's an 'rdmsr' or 'wrmsr'.

typedef enum _DEBUGGER_MSR_ACTION_TYPE { DEBUGGER_MSR_READ, DEBUGGER_MSR_WRITE } DEBUGGER_MSR_ACTION_TYPE;

{% hint style="info" %} If you want to execute 'wrmsr' or 'rdmsr', you should set CoreNumber to DEBUGGER_READ_AND_WRITE_ON_MSR_APPLY_ALL_CORES. {% endhint %}

#define DEBUGGER_READ_AND_WRITE_ON_MSR_APPLY_ALL_CORES 0xffffffff

Remarks

This command will continue the debuggee for some time (in Debugger Mode). This means that you lose the current context (registers & memory) after executing this command.

Requirements

None

Related

wrmsr (write model-specific register)