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Intel® Trust Domain Extensions (Intel® TDX) is an Intel technology that expands Virtual Machine Extensions (VMX) with a new type of virtual machine guest known as a Trust Domain (TD).

A TD is intended to secure the confidentiality of its memory contents, CPU state, and so on. This patch set aims to develop a TDX compliance test suite to verify the TDX's consistency to the specification, preventing potential security risks in the TD environment.

TDX compliance tests contain a series of compliance tests, including CPUID, CR, MSR. They are designed to verify the security and functionality of the TD environment, which should work exactly as designed in the TDX Specification. That will increase the credibility of Intel TDX.

Usage

TDX-compliance is designed to work as a kernel module. Before using it, you need to build it.

Step 1: Prepare your environment to build kernel modules

Build and install the kernel locally (in TD guest) Install the source code from distribution

Step 2: Build tdx-compliance

To build tdx-compliance, follow these steps:

git clone https://github.com/intel/lkvs.git
cd lkvs/BM/tdx-compliance
make
insmod tdx-compliance.ko

Step 3: Run test cases

To run all kinds of compliance tests, simply enter the following command:

echo all [version]> /sys/kernel/debug/tdx/tdx-tests

the compliance tests of all versions will be tested in default.

If you want to test against a specific TDX-Module version, use [version] option, the currently selectable version is "1.0" or "1.5".

To view the results and logs, use this command:

cat /sys/kernel/debug/tdx/tdx-tests

If you want to learn more about tdx-compliance, please refer to the following resources.

  • CPUID

CPUID compliance is part of TDX-compliance tests to make sure whether the current virtualized TD environment is compliant with the CPUID instruction, especially for the ones with fixed type, confirming the expected outputs, and no exceptions occur.

A CPUID compliance test calls the instruction 'cpuid' with leaf or sub-leaf specified, then check the bits of outputs. All tests are from the table 2.4(CPUID Virtualization Overview) in Intel® Trust Domain Extensions (Intel® TDX) Module Architecture Application Binary Interface (ABI) Reference Specification

Users can execute the compliance test and dump results via the Kernel interface /sys/kernel/debug/tdx/tdx-tests.

Usage: Run cpuid compliance tests:

echo cpuid [version] > /sys/kernel/debug/tdx/tdx-tests
  • MSR

The Model Specific Registers (MSR) are special registers in the CPU that store information related to the processor model. Intel TDX virtualizes the behavior of the MSRs' read and write.

Usage: Run MSR compliance tests:

each msr [version] > /sys/kernel/debug/tdx/tdx-tests
  • CR(Control Registers)

CR(Control Register) is a set of registers in the processor used to control operations. They contain many different control bits that are used to control how the processor operates. For example, control bits in the CR0 can be used to enable or disable the pagination mechanism, etc.

Usage:

echo cr [version] > /sys/kernel/debug/tdx/tdx-tests
  • Trigger the cpuid and capture #VE or #GP.

Some CPUID instructions will trigger #VE (Virtualization Exceptions), and during the process of handling #VE, the tdx_handle_virt_exception function is called. Based on the return value of this function, it can be determined whether it is #VE or #GP. The #VE triggered by the CPUID instruction will ultimately be handled by the handle_cpuid function, and the return value of this function determines the return value of the tdx_handle_virt_exception function. Therefore, it is necessary to capture the return value of the handle_cpuid function. We use the kernel-provided kretprobe mechanism to capture the return value of the handle_cpuid function, thereby determining whether it is #VE or #GP.

Usage: Register probe points:

echo kretprobe > /sys/kernel/debug/tdx/tdx-tests

Single trigger cpuid instruction, and the captured information is printed in dmesg. 0x1f 0x0 0x0 0x0 are the input of eax, ebx, ecx, edx.:

echo trigger_cpuid 0x1f 0x0 0x0 0x0 > /sys/kernel/debug/tdx/tdx-tests

Trigger all cpuid instructions in tdx-compliance.h：

echo cpuid > /sys/kernel/debug/tdx/tdx-tests

Unregister the kretprobe:

echo unregister > /sys/kernel/debug/tdx/tdx-tests
rmmod tdx_compliance

Note: Executing the CPUID instruction in user space can lead to contamination, resulting in multiple captures of handle_cpuid; therefore, the most accurate method is to trigger the CPUID instruction in kernel space.

Contact:

Sun, Yi ([email protected])