Patchwork [V27,5/7] Add a TPM Passthrough backend driver implementation

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Submitter Stefan Berger
Date Feb. 27, 2013, 5:47 p.m.
Message ID <1361987275-26289-6-git-send-email-stefanb@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/223668/
State New
Headers show

Comments

Stefan Berger - Feb. 27, 2013, 5:47 p.m.
From Andreas Niederl's original posting with adaptations where necessary:

This patch is based of off version 9 of Stefan Berger's patch series
  "QEMU Trusted Platform Module (TPM) integration"
and adds a new backend driver for it.

This patch adds a passthrough backend driver for passing commands sent to the
emulated TPM device directly to a TPM device opened on the host machine.
Thus it is possible to use a hardware TPM device in a system running on QEMU,
providing the ability to access a TPM in a special state (e.g. after a Trusted
Boot).

This functionality is being used in the acTvSM Trusted Virtualization Platform
which is available on [1].

Usage example:
  qemu-system-x86_64 -tpmdev passthrough,id=tpm0,path=/dev/tpm0 \
                     -device tpm-tis,tpmdev=tpm0 \
                     -cdrom test.iso -boot d

Some notes about the host TPM:
The TPM needs to be enabled and activated. If that's not the case one
has to go through the BIOS/UEFI and enable and activate that TPM for TPM
commands to work as expected.
It may be necessary to boot the kernel using tpm_tis.force=1 in the boot
command line or 'modprobe tpm_tis force=1' in case of using it as a module.

Regards,
Andreas Niederl, Stefan Berger

[1] http://trustedjava.sourceforge.net/

Signed-off-by: Andreas Niederl <andreas.niederl@iaik.tugraz.at>
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
---
 include/qemu/sockets.h |   1 +
 qemu-char.c            |  24 +++
 qemu-options.hx        |  36 ++++-
 tpm/Makefile.objs      |   2 +
 tpm/tpm.c              |  14 ++
 tpm/tpm_backend.c      |  58 ++++++++
 tpm/tpm_backend.h      |  45 ++++++
 tpm/tpm_int.h          |  33 +++++
 tpm/tpm_passthrough.c  | 387 +++++++++++++++++++++++++++++++++++++++++++++++++
 9 files changed, 599 insertions(+), 1 deletion(-)
 create mode 100644 tpm/tpm_backend.c
 create mode 100644 tpm/tpm_backend.h
 create mode 100644 tpm/tpm_passthrough.c

Patch

diff --git a/include/qemu/sockets.h b/include/qemu/sockets.h
index 803ae17..16569e2 100644
--- a/include/qemu/sockets.h
+++ b/include/qemu/sockets.h
@@ -37,6 +37,7 @@  int socket_set_cork(int fd, int v);
 void socket_set_block(int fd);
 void socket_set_nonblock(int fd);
 int send_all(int fd, const void *buf, int len1);
+int recv_all(int fd, void *buf, int len1, bool single_read);
 
 /* callback function for nonblocking connect
  * valid fd on success, negative error code on failure
diff --git a/qemu-char.c b/qemu-char.c
index 160decc..a8de655 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -537,6 +537,30 @@  int send_all(int fd, const void *_buf, int len1)
     }
     return len1 - len;
 }
+
+int recv_all(int fd, void *_buf, int len1, bool single_read)
+{
+    int ret, len;
+    uint8_t *buf = _buf;
+
+    len = len1;
+    while ((len > 0) && (ret = read(fd, buf, len)) != 0) {
+        if (ret < 0) {
+            if (errno != EINTR && errno != EAGAIN) {
+                return -1;
+            }
+            continue;
+        } else {
+            if (single_read) {
+                return ret;
+            }
+            buf += ret;
+            len -= ret;
+        }
+    }
+    return len1 - len;
+}
+
 #endif /* !_WIN32 */
 
 #define STDIO_MAX_CLIENTS 1
diff --git a/qemu-options.hx b/qemu-options.hx
index 3c31806..97723a7 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2222,7 +2222,8 @@  DEFHEADING()
 DEFHEADING(TPM device options:)
 
 DEF("tpmdev", HAS_ARG, QEMU_OPTION_tpmdev, \
-    "-tpmdev [<type>],id=str[,option][,option][,...]\n",
+    "-tpmdev passthrough,id=id[,path=path]\n"
+    "                use path to provide path to a character device; default is /dev/tpm0\n",
     QEMU_ARCH_ALL)
 STEXI
 
@@ -2232,6 +2233,7 @@  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}.
 
 The specific backend type will determine the applicable options.
 The @code{-tpmdev} option requires a @code{-device} option.
@@ -2243,6 +2245,38 @@  Use 'help' to print all available TPM backend types.
 qemu -tpmdev help
 @end example
 
+@item -tpmdev passthrough, id=@var{id}, path=@var{path}
+
+(Linux-host only) Enable access to the host's TPM using the passthrough
+driver.
+
+@option{path} specifies the path to the host's TPM device, i.e., on
+a Linux host this would be @code{/dev/tpm0}.
+@option{path} is optional and by default @code{/dev/tpm0} is used.
+
+Some notes about using the host's TPM with the passthrough driver:
+
+The TPM device accessed by the passthrough driver must not be
+used by any other application on the host.
+
+Since the host's firmware (BIOS/UEFI) has already initialized the TPM,
+the VM's firmware (BIOS/UEFI) will not be able to initialize the
+TPM again and may therefore not show a TPM-specific menu that would
+otherwise allow the user to configure the TPM, e.g., allow the user to
+enable/disable or activate/deactivate the TPM.
+Further, if TPM ownership is released from within a VM then the host's TPM
+will get disabled and deactivated. To enable and activate the
+TPM again afterwards, the host has to be rebooted and the user is
+required to enter the firmware's menu to enable and activate the TPM.
+If the TPM is left disabled and/or deactivated most TPM commands will fail.
+
+To create a passthrough TPM use the following two options:
+@example
+-tpmdev passthrough,id=tpm0 -device tpm-tis,tpmdev=tpm0
+@end example
+Note that the @code{-tpmdev} id is @code{tpm0} and is referenced by
+@code{tpmdev=tpm0} in the device option.
+
 @end table
 
 ETEXI
diff --git a/tpm/Makefile.objs b/tpm/Makefile.objs
index 94ad2e7..8676824 100644
--- a/tpm/Makefile.objs
+++ b/tpm/Makefile.objs
@@ -1,4 +1,6 @@ 
 common-obj-y = tpm.o
 ifeq ($(CONFIG_TPM),y)
+common-obj-y += tpm_backend.o
 common-obj-$(CONFIG_TPM_TIS) += tpm_tis.o
+common-obj-$(CONFIG_TPM_PASSTHROUGH) += tpm_passthrough.o
 endif
diff --git a/tpm/tpm.c b/tpm/tpm.c
index 0273549..ffd2495 100644
--- a/tpm/tpm.c
+++ b/tpm/tpm.c
@@ -61,6 +61,20 @@  static bool tpm_model_is_registered(enum TpmModel model)
     return false;
 }
 
+/*
+ * Write an error message in the given output buffer.
+ */
+void tpm_write_fatal_error_response(uint8_t *out, uint32_t out_len)
+{
+    if (out_len >= sizeof(struct tpm_resp_hdr)) {
+        struct tpm_resp_hdr *resp = (struct tpm_resp_hdr *)out;
+
+        resp->tag = cpu_to_be16(TPM_TAG_RSP_COMMAND);
+        resp->len = cpu_to_be32(sizeof(struct tpm_resp_hdr));
+        resp->errcode = cpu_to_be32(TPM_FAIL);
+    }
+}
+
 const TPMDriverOps *tpm_get_backend_driver(const char *type)
 {
     int i;
diff --git a/tpm/tpm_backend.c b/tpm/tpm_backend.c
new file mode 100644
index 0000000..4144ef7
--- /dev/null
+++ b/tpm/tpm_backend.c
@@ -0,0 +1,58 @@ 
+/*
+ *  common TPM backend driver functions
+ *
+ *  Copyright (c) 2012-2013 IBM Corporation
+ *  Authors:
+ *    Stefan Berger <stefanb@us.ibm.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>
+ */
+
+#include "tpm/tpm.h"
+#include "qemu/thread.h"
+#include "tpm_backend.h"
+
+void tpm_backend_thread_deliver_request(TPMBackendThread *tbt)
+{
+   g_thread_pool_push(tbt->pool, (gpointer)TPM_BACKEND_CMD_PROCESS_CMD, NULL);
+}
+
+void tpm_backend_thread_create(TPMBackendThread *tbt,
+                               GFunc func, gpointer user_data)
+{
+    if (!tbt->pool) {
+        tbt->pool = g_thread_pool_new(func, user_data, 1, TRUE, NULL);
+        g_thread_pool_push(tbt->pool, (gpointer)TPM_BACKEND_CMD_INIT, NULL);
+    }
+}
+
+void tpm_backend_thread_end(TPMBackendThread *tbt)
+{
+    if (tbt->pool) {
+        g_thread_pool_push(tbt->pool, (gpointer)TPM_BACKEND_CMD_END, NULL);
+        g_thread_pool_free(tbt->pool, FALSE, TRUE);
+        tbt->pool = NULL;
+    }
+}
+
+void tpm_backend_thread_tpm_reset(TPMBackendThread *tbt,
+                                  GFunc func, gpointer user_data)
+{
+    if (!tbt->pool) {
+        tpm_backend_thread_create(tbt, func, user_data);
+    } else {
+        g_thread_pool_push(tbt->pool, (gpointer)TPM_BACKEND_CMD_TPM_RESET,
+                           NULL);
+    }
+}
diff --git a/tpm/tpm_backend.h b/tpm/tpm_backend.h
new file mode 100644
index 0000000..05d94d0
--- /dev/null
+++ b/tpm/tpm_backend.h
@@ -0,0 +1,45 @@ 
+/*
+ *  common TPM backend driver functions
+ *
+ *  Copyright (c) 2012-2013 IBM Corporation
+ *  Authors:
+ *    Stefan Berger <stefanb@us.ibm.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>
+ */
+
+#ifndef TPM_TPM_BACKEND_H
+#define TPM_TPM_BACKEND_H
+
+#include <glib.h>
+
+typedef struct TPMBackendThread {
+    GThreadPool *pool;
+} TPMBackendThread;
+
+void tpm_backend_thread_deliver_request(TPMBackendThread *tbt);
+void tpm_backend_thread_create(TPMBackendThread *tbt,
+                               GFunc func, gpointer user_data);
+void tpm_backend_thread_end(TPMBackendThread *tbt);
+void tpm_backend_thread_tpm_reset(TPMBackendThread *tbt,
+                                  GFunc func, gpointer user_data);
+
+typedef enum TPMBackendCmd {
+    TPM_BACKEND_CMD_INIT = 1,
+    TPM_BACKEND_CMD_PROCESS_CMD,
+    TPM_BACKEND_CMD_END,
+    TPM_BACKEND_CMD_TPM_RESET,
+} TPMBackendCmd;
+
+#endif /* TPM_TPM_BACKEND_H */
diff --git a/tpm/tpm_int.h b/tpm/tpm_int.h
index d5358ad..f705643 100644
--- a/tpm/tpm_int.h
+++ b/tpm/tpm_int.h
@@ -18,6 +18,8 @@ 
 struct TPMDriverOps;
 typedef struct TPMDriverOps TPMDriverOps;
 
+typedef struct TPMPassthruState TPMPassthruState;
+
 typedef struct TPMBackend {
     char *id;
     enum TpmModel fe_model;
@@ -25,6 +27,10 @@  typedef struct TPMBackend {
     char *cancel_path;
     const TPMDriverOps *ops;
 
+    union {
+        TPMPassthruState *tpm_pt;
+    } s;
+
     QLIST_ENTRY(TPMBackend) list;
 } TPMBackend;
 
@@ -74,10 +80,37 @@  struct TPMDriverOps {
     bool (*get_tpm_established_flag)(TPMBackend *t);
 };
 
+struct tpm_req_hdr {
+    uint16_t tag;
+    uint32_t len;
+    uint32_t ordinal;
+} QEMU_PACKED;
+
+struct tpm_resp_hdr {
+    uint16_t tag;
+    uint32_t len;
+    uint32_t errcode;
+} QEMU_PACKED;
+
+#define TPM_TAG_RQU_COMMAND       0xc1
+#define TPM_TAG_RQU_AUTH1_COMMAND 0xc2
+#define TPM_TAG_RQU_AUTH2_COMMAND 0xc3
+
+#define TPM_TAG_RSP_COMMAND       0xc4
+#define TPM_TAG_RSP_AUTH1_COMMAND 0xc5
+#define TPM_TAG_RSP_AUTH2_COMMAND 0xc6
+
+#define TPM_FAIL                  9
+
+#define TPM_ORD_GetTicks          0xf1
+
 TPMBackend *qemu_find_tpm(const char *id);
 int tpm_register_model(enum TpmModel model);
 int tpm_register_driver(const TPMDriverOps *tdo);
 void tpm_display_backend_drivers(void);
 const TPMDriverOps *tpm_get_backend_driver(const char *type);
+void tpm_write_fatal_error_response(uint8_t *out, uint32_t out_len);
+
+extern const TPMDriverOps tpm_passthrough_driver;
 
 #endif /* TPM_TPM_INT_H */
diff --git a/tpm/tpm_passthrough.c b/tpm/tpm_passthrough.c
new file mode 100644
index 0000000..760e18f
--- /dev/null
+++ b/tpm/tpm_passthrough.c
@@ -0,0 +1,387 @@ 
+/*
+ *  passthrough TPM driver
+ *
+ *  Copyright (c) 2010 - 2013 IBM Corporation
+ *  Authors:
+ *    Stefan Berger <stefanb@us.ibm.com>
+ *
+ *  Copyright (C) 2011 IAIK, Graz University of Technology
+ *    Author: Andreas Niederl
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>
+ */
+
+#include "qemu-common.h"
+#include "qapi/error.h"
+#include "qemu/sockets.h"
+#include "tpm_int.h"
+#include "hw/hw.h"
+#include "hw/pc.h"
+#include "tpm_tis.h"
+#include "tpm_backend.h"
+
+/* #define DEBUG_TPM */
+
+#ifdef DEBUG_TPM
+#define DPRINTF(fmt, ...) \
+    do { fprintf(stderr, fmt, ## __VA_ARGS__); } while (0)
+#else
+#define DPRINTF(fmt, ...) \
+    do { } while (0)
+#endif
+
+/* data structures */
+
+typedef struct TPMPassthruThreadParams {
+    TPMState *tpm_state;
+
+    TPMRecvDataCB *recv_data_callback;
+    TPMBackend *tb;
+} TPMPassthruThreadParams;
+
+struct TPMPassthruState {
+    TPMBackendThread tbt;
+
+    TPMPassthruThreadParams tpm_thread_params;
+
+    char *tpm_dev;
+    int tpm_fd;
+    bool had_startup_error;
+};
+
+#define TPM_PASSTHROUGH_DEFAULT_DEVICE "/dev/tpm0"
+
+static int tpm_passthrough_unix_write(int fd, const uint8_t *buf, uint32_t len)
+{
+    return send_all(fd, buf, len);
+}
+
+static int tpm_passthrough_unix_read(int fd, uint8_t *buf, uint32_t len)
+{
+    return recv_all(fd, buf, len, true);
+}
+
+static uint32_t tpm_passthrough_get_size_from_buffer(const uint8_t *buf)
+{
+    struct tpm_resp_hdr *resp = (struct tpm_resp_hdr *)buf;
+
+    return be32_to_cpu(resp->len);
+}
+
+static int tpm_passthrough_unix_tx_bufs(int tpm_fd,
+                                        const uint8_t *in, uint32_t in_len,
+                                        uint8_t *out, uint32_t out_len)
+{
+    int ret;
+
+    ret = tpm_passthrough_unix_write(tpm_fd, in, in_len);
+    if (ret != in_len) {
+        error_report("tpm_passthrough: error while transmitting data "
+                     "to TPM: %s (%i)\n",
+                     strerror(errno), errno);
+        goto err_exit;
+    }
+
+    ret = tpm_passthrough_unix_read(tpm_fd, out, out_len);
+    if (ret < 0) {
+        error_report("tpm_passthrough: error while reading data from "
+                     "TPM: %s (%i)\n",
+                     strerror(errno), errno);
+    } else if (ret < sizeof(struct tpm_resp_hdr) ||
+               tpm_passthrough_get_size_from_buffer(out) != ret) {
+        ret = -1;
+        error_report("tpm_passthrough: received invalid response "
+                     "packet from TPM\n");
+    }
+
+err_exit:
+    if (ret < 0) {
+        tpm_write_fatal_error_response(out, out_len);
+    }
+
+    return ret;
+}
+
+static int tpm_passthrough_unix_transfer(int tpm_fd,
+                                         const TPMLocality *locty_data)
+{
+    return tpm_passthrough_unix_tx_bufs(tpm_fd,
+                                        locty_data->w_buffer.buffer,
+                                        locty_data->w_offset,
+                                        locty_data->r_buffer.buffer,
+                                        locty_data->r_buffer.size);
+}
+
+static void tpm_passthrough_worker_thread(gpointer data,
+                                          gpointer user_data)
+{
+    TPMPassthruThreadParams *thr_parms = user_data;
+    TPMPassthruState *tpm_pt = thr_parms->tb->s.tpm_pt;
+    TPMBackendCmd cmd = (TPMBackendCmd)data;
+
+    DPRINTF("tpm_passthrough: processing command type %d\n", cmd);
+
+    switch (cmd) {
+    case TPM_BACKEND_CMD_PROCESS_CMD:
+        tpm_passthrough_unix_transfer(tpm_pt->tpm_fd,
+                                      thr_parms->tpm_state->locty_data);
+
+        thr_parms->recv_data_callback(thr_parms->tpm_state,
+                                      thr_parms->tpm_state->locty_number);
+        break;
+    case TPM_BACKEND_CMD_INIT:
+    case TPM_BACKEND_CMD_END:
+    case TPM_BACKEND_CMD_TPM_RESET:
+        /* nothing to do */
+        break;
+    }
+}
+
+/*
+ * Start the TPM (thread). If it had been started before, then terminate
+ * and start it again.
+ */
+static int tpm_passthrough_startup_tpm(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+    /* terminate a running TPM */
+    tpm_backend_thread_end(&tpm_pt->tbt);
+
+    tpm_backend_thread_create(&tpm_pt->tbt,
+                              tpm_passthrough_worker_thread,
+                              &tb->s.tpm_pt->tpm_thread_params);
+
+    return 0;
+}
+
+static void tpm_passthrough_reset(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+    DPRINTF("tpm_passthrough: CALL TO TPM_RESET!\n");
+
+    tpm_backend_thread_end(&tpm_pt->tbt);
+
+    tpm_pt->had_startup_error = false;
+}
+
+static int tpm_passthrough_init(TPMBackend *tb, TPMState *s,
+                                TPMRecvDataCB *recv_data_cb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+    tpm_pt->tpm_thread_params.tpm_state = s;
+    tpm_pt->tpm_thread_params.recv_data_callback = recv_data_cb;
+    tpm_pt->tpm_thread_params.tb = tb;
+
+    return 0;
+}
+
+static bool tpm_passthrough_get_tpm_established_flag(TPMBackend *tb)
+{
+    return false;
+}
+
+static bool tpm_passthrough_get_startup_error(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+    return tpm_pt->had_startup_error;
+}
+
+static size_t tpm_passthrough_realloc_buffer(TPMSizedBuffer *sb)
+{
+    size_t wanted_size = 4096; /* Linux tpm.c buffer size */
+
+    if (sb->size != wanted_size) {
+        sb->buffer = g_realloc(sb->buffer, wanted_size);
+        sb->size = wanted_size;
+    }
+    return sb->size;
+}
+
+static void tpm_passthrough_deliver_request(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+    tpm_backend_thread_deliver_request(&tpm_pt->tbt);
+}
+
+static void tpm_passthrough_cancel_cmd(TPMBackend *tb)
+{
+    /* cancelling an ongoing command is known not to work with some TPMs */
+}
+
+static const char *tpm_passthrough_create_desc(void)
+{
+    return "Passthrough TPM backend driver";
+}
+
+/*
+ * A basic test of a TPM device. We expect a well formatted response header
+ * (error response is fine) within one second.
+ */
+static int tpm_passthrough_test_tpmdev(int fd)
+{
+    struct tpm_req_hdr req = {
+        .tag = cpu_to_be16(TPM_TAG_RQU_COMMAND),
+        .len = cpu_to_be32(sizeof(req)),
+        .ordinal = cpu_to_be32(TPM_ORD_GetTicks),
+    };
+    struct tpm_resp_hdr *resp;
+    fd_set readfds;
+    int n;
+    struct timeval tv = {
+        .tv_sec = 1,
+        .tv_usec = 0,
+    };
+    unsigned char buf[1024];
+
+    n = write(fd, &req, sizeof(req));
+    if (n < 0) {
+        return errno;
+    }
+    if (n != sizeof(req)) {
+        return EFAULT;
+    }
+
+    FD_ZERO(&readfds);
+    FD_SET(fd, &readfds);
+
+    /* wait for a second */
+    n = select(fd + 1, &readfds, NULL, NULL, &tv);
+    if (n != 1) {
+        return errno;
+    }
+
+    n = read(fd, &buf, sizeof(buf));
+    if (n < sizeof(struct tpm_resp_hdr)) {
+        return EFAULT;
+    }
+
+    resp = (struct tpm_resp_hdr *)buf;
+    /* check the header */
+    if (be16_to_cpu(resp->tag) != TPM_TAG_RSP_COMMAND ||
+        be32_to_cpu(resp->len) != n) {
+        return EBADMSG;
+    }
+
+    return 0;
+}
+
+static int tpm_passthrough_handle_device_opts(QemuOpts *opts, TPMBackend *tb)
+{
+    const char *value;
+
+    value = qemu_opt_get(opts, "path");
+    if (!value) {
+        value = TPM_PASSTHROUGH_DEFAULT_DEVICE;
+    }
+
+    tb->s.tpm_pt->tpm_dev = g_strdup(value);
+
+    tb->path = g_strdup(tb->s.tpm_pt->tpm_dev);
+
+    tb->s.tpm_pt->tpm_fd = qemu_open(tb->s.tpm_pt->tpm_dev, O_RDWR);
+    if (tb->s.tpm_pt->tpm_fd < 0) {
+        error_report("Cannot access TPM device using '%s': %s\n",
+                     tb->s.tpm_pt->tpm_dev, strerror(errno));
+        goto err_free_parameters;
+    }
+
+    if (tpm_passthrough_test_tpmdev(tb->s.tpm_pt->tpm_fd)) {
+        error_report("'%s' is not a TPM device.\n",
+                     tb->s.tpm_pt->tpm_dev);
+        goto err_close_tpmdev;
+    }
+
+    return 0;
+
+ err_close_tpmdev:
+    qemu_close(tb->s.tpm_pt->tpm_fd);
+    tb->s.tpm_pt->tpm_fd = -1;
+
+ err_free_parameters:
+    g_free(tb->path);
+    tb->path = NULL;
+
+    g_free(tb->s.tpm_pt->tpm_dev);
+    tb->s.tpm_pt->tpm_dev = NULL;
+
+    return 1;
+}
+
+static TPMBackend *tpm_passthrough_create(QemuOpts *opts, const char *id)
+{
+    TPMBackend *tb;
+
+    tb = g_new0(TPMBackend, 1);
+    tb->s.tpm_pt = g_new0(TPMPassthruState, 1);
+    tb->id = g_strdup(id);
+    /* let frontend set the fe_model to proper value */
+    tb->fe_model = -1;
+
+    tb->ops = &tpm_passthrough_driver;
+
+    if (tpm_passthrough_handle_device_opts(opts, tb)) {
+        goto err_exit;
+    }
+
+    return tb;
+
+err_exit:
+    g_free(tb->id);
+    g_free(tb->s.tpm_pt);
+    g_free(tb);
+
+    return NULL;
+}
+
+static void tpm_passthrough_destroy(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+    tpm_backend_thread_end(&tpm_pt->tbt);
+
+    qemu_close(tpm_pt->tpm_fd);
+
+    g_free(tb->id);
+    g_free(tb->path);
+    g_free(tb->s.tpm_pt->tpm_dev);
+    g_free(tb->s.tpm_pt);
+    g_free(tb);
+}
+
+const TPMDriverOps tpm_passthrough_driver = {
+    .type                     = TPM_TYPE_PASSTHROUGH,
+    .desc                     = tpm_passthrough_create_desc,
+    .create                   = tpm_passthrough_create,
+    .destroy                  = tpm_passthrough_destroy,
+    .init                     = tpm_passthrough_init,
+    .startup_tpm              = tpm_passthrough_startup_tpm,
+    .realloc_buffer           = tpm_passthrough_realloc_buffer,
+    .reset                    = tpm_passthrough_reset,
+    .had_startup_error        = tpm_passthrough_get_startup_error,
+    .deliver_request          = tpm_passthrough_deliver_request,
+    .cancel_cmd               = tpm_passthrough_cancel_cmd,
+    .get_tpm_established_flag = tpm_passthrough_get_tpm_established_flag,
+};
+
+static void tpm_passthrough_register(void)
+{
+    tpm_register_driver(&tpm_passthrough_driver);
+}
+
+type_init(tpm_passthrough_register)