tpm: Added support for TPM emulator

This change introduces a new TPM backend driver that can communicate with
swtpm(software TPM emulator) using unix domain socket interface. QEMU talks to
the TPM emulator using QEMU's socket-based chardev backend device.

Swtpm uses two Unix sockets for communications, one for plain TPM commands and
responses, and one for out-of-band control messages. QEMU passes the data
socket to be used over the control channel.

The swtpm and associated tools can be found here:
    https://github.com/stefanberger/swtpm

The swtpm's control channel protocol specification can be found here:
    https://github.com/stefanberger/swtpm/wiki/Control-Channel-Specification

Usage:
    # setup TPM state directory
    mkdir /tmp/mytpm
    chown -R tss:root /tmp/mytpm
    /usr/bin/swtpm_setup --tpm-state /tmp/mytpm --createek

    # Ask qemu to use TPM emulator with given tpm state directory
    qemu-system-x86_64 \
        [...] \
        -chardev socket,id=chrtpm,path=/tmp/swtpm-sock \
        -tpmdev emulator,id=tpm0,chardev=chrtpm \
        -device tpm-tis,tpmdev=tpm0 \
        [...]

Signed-off-by: Amarnath Valluri <amarnath.valluri@intel.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>

1 files changed, 19 insertions, 3 deletions

diff --git a/qemu-options.hx b/qemu-options.hx
index 981742d..3728e9b 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3121,7 +3121,9 @@ DEF("tpmdev", HAS_ARG, QEMU_OPTION_tpmdev, \
     "-tpmdev passthrough,id=id[,path=path][,cancel-path=path]\n"
     "                use path to provide path to a character device; default is /dev/tpm0\n"
     "                use cancel-path to provide path to TPM's cancel sysfs entry; if\n"
-    "                not provided it will be searched for in /sys/class/misc/tpm?/device\n",
+    "                not provided it will be searched for in /sys/class/misc/tpm?/device\n"
+    "-tpmdev emulator,id=id,chardev=dev\n"
+    "                configure the TPM device using chardev backend\n",
     QEMU_ARCH_ALL)
 STEXI
 
@@ -3130,8 +3132,8 @@ The general form of a TPM device option is:
 
 @item -tpmdev @var{backend} ,id=@var{id} [,@var{options}]
 @findex -tpmdev
-Backend type must be:
-@option{passthrough}.
+Backend type must be either one of the following:
+@option{passthrough}, @option{emulator}.
 
 The specific backend type will determine the applicable options.
 The @code{-tpmdev} option creates the TPM backend and requires a
@@ -3181,6 +3183,20 @@ To create a passthrough TPM use the following two options:
 Note that the @code{-tpmdev} id is @code{tpm0} and is referenced by
 @code{tpmdev=tpm0} in the device option.
 
+@item -tpmdev emulator, id=@var{id}, chardev=@var{dev}
+
+(Linux-host only) Enable access to a TPM emulator using Unix domain socket based
+chardev backend.
+
+@option{chardev} specifies the unique ID of a character device backend that provides connection to the software TPM server.
+
+To create a TPM emulator backend device with chardev socket backend:
+@example
+
+-chardev socket,id=chrtpm,path=/tmp/swtpm-sock -tpmdev emulator,id=tpm0,chardev=chrtpm -device tpm-tis,tpmdev=tpm0
+
+@end example
+
 @end table
 
 ETEXI