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Virtualization Guide / Hypervisor-independent features / Software TPM emulator
Applies to openSUSE Leap 15.4

20 Software TPM emulator

  

20.1 Introduction

  

The Trusted Platform Module (TPM) is a cryptoprocessor that secures hardware using cryptographic keys. For developers who use the TPM to develop security features, a software TPM emulator is a convenient solution. Compared to a hardware TPM device, the emulator has no limit on the number of guests that can access it. Also, it is simple to switch between TPM versions 1.2 and 2.0. QEMU supports the software TPM emulator that is included in the swtpm package.

20.2 Prerequisites

  

Before you can install and use the software TPM emulator, you need to install the libvirt virtualization environment. Refer to Section 6.2, “Installing virtualization components” and install one of the provided virtualization solutions.

20.3 Installation

  

To use the software TPM emulator, install the swtpm package: 

> sudo zypper install swtpm

20.4 Using swtpm with QEMU

  

swtpm provides three types of interface: socket, chardev, and cuse. This procedure focuses on the socket interface.

  1. Create a directory mytpm0 inside the VM directory to store the TPM states—for example, /var/lib/libvirt/qemu/sle15sp3: 

    > sudo mkdir /var/lib/libvirt/qemu/sle15sp3/mytpm0

  2. Start swtmp. It will create a socket file that QEMU can use—for example, /var/lib/libvirt/qemu/sle15sp3: 

     > sudo swtpm socket
  --tpmstate dir=/var/lib/libvirt/qemu/sle15sp3/mytpm0 \
  --ctrl type=unixio,path=/var/lib/libvirt/qemu/sle15sp3/mytpm0/swtpm-sock \
  --log level=20
    Tip
    Tip: TPM version 2.0

    By default, swtpm starts a TPM version 1.2 emulator and stores its states in the tpm-00.permall directory. To create a TPM 2.0 instance, run: 

     > sudo swtpm socket
  --tpm2
  --tpmstate dir=/var/lib/libvirt/qemu/sle15sp3/mytpm0 \
  --ctrl type=unixio,path=/var/lib/libvirt/qemu/sle15sp3/mytpm0/swtpm-sock \
  --log level=20

    TPM 2.0 states will be stored in the tpm2-00.permall directory.

  3. Add the following command line parameters to the qemu-system-ARCH command: 

    > qemu-system-x86_64 \
[...]
-chardev socket,id=chrtpm,path=/var/lib/libvirt/qemu/sle15sp3/mytpm0/swtpm-sock \
-tpmdev emulator,id=tpm0,chardev=chrtpm \
-device tpm-tis,tpmdev=tpm0

  4. Verify that the TPM device is available in the guest by running the following command: 

    > tpm_version
TPM 1.2 Version Info:
Chip Version:        1.2.18.158
Spec Level:          2
Errata Revision:     3
TPM Vendor ID:       IBM
TPM Version:         01010000
Manufacturer Info:   49424d00

20.5 Using swtpm with libvirt

  

To use swtpm with libvirt, add the following TPM device to the guest XML specification: 

<devices>
 <tpm model='tpm-tis'>
  <backend type='emulator' version='2.0'/>
 </tpm>
</devices>

libvirt will start swtpm for the guest automatically; you do not need to start it manually in advance. The corresponding permall file will be created in /var/lib/libvirt/swtpm/VM_UUID.

20.6 TPM measurement with OVMF firmware

  

If the guest uses the Open Virtual Machine Firmware (OVMF), it will measure components with TPM. You can find the event log in /sys/kernel/security/tpm0/binary_bios_measurements.

20.7 Resources