[Qemu-devel] [PATCH V11 5/5] Add a TPM Passthrough backend driver implementation

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

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>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.

Changes for v10:
 - clarified documentation
 - using /dev/tpm0 as default device if path option is not given
 - refactored code handling 'device' option into its own function
 - fixed name of structure to TPMPassthruThreadParams
 - only add tpm_passthrough_driver to collection of backends if
   it is compiled on the host

Changes for v9:
 - prefixing of all functions and variables with tpm_passthrough_
 - cleanup of all variables into a structure that is now accessed
   using TPMBackend (tb->s.tpm_pt)
 - build it on Linux machines
 - added function to test whether given device is a TPM and refuse
   startup if it is not

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>

---
 Makefile.target      |    1 
 configure            |    3 
 hw/tpm_passthrough.c |  471 +++++++++++++++++++++++++++++++++++++++++++++++++++
 qemu-options.hx      |   33 +++
 tpm.c                |   23 ++
 tpm.h                |   34 +++
 6 files changed, 565 insertions(+)
 create mode 100644 hw/tpm_passthrough.c

Index: qemu-git.pt/Makefile.target
===================================================================
--- qemu-git.pt.orig/Makefile.target
+++ qemu-git.pt/Makefile.target
@@ -195,6 +195,7 @@ obj-$(CONFIG_KVM) += kvm.o kvm-all.o
 obj-$(CONFIG_NO_KVM) += kvm-stub.o
 obj-y += memory.o
 obj-$(CONFIG_TPM) += tpm.o tpm_tis.o
+obj-$(CONFIG_TPM_PASSTHROUGH) += tpm_passthrough.o
 LIBS+=-lz
 
 QEMU_CFLAGS += $(VNC_TLS_CFLAGS)
Index: qemu-git.pt/configure
===================================================================
--- qemu-git.pt.orig/configure
+++ qemu-git.pt/configure
@@ -3565,6 +3565,9 @@ fi
 
 if test "$tpm" = "yes"; then
   if test "$target_softmmu" = "yes" ; then
+    if test "$linux" = "yes" ; then
+      echo "CONFIG_TPM_PASSTHROUGH=y" >> $config_target_mak
+    fi
     echo "CONFIG_TPM=y" >> $config_host_mak
   fi
 fi
Index: qemu-git.pt/hw/tpm_passthrough.c
===================================================================
--- /dev/null
+++ qemu-git.pt/hw/tpm_passthrough.c
@@ -0,0 +1,471 @@
+/*
+ *  passthrough TPM driver
+ *
+ *  Copyright (c) 2010, 2011 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 "qemu-error.h"
+#include "tpm.h"
+#include "hw/hw.h"
+#include "hw/tpm_tis.h"
+#include "hw/pc.h"
+
+/* #define DEBUG_TPM */
+
+/* data structures */
+
+typedef struct TPMPassthruThreadParams {
+    TPMState *tpm_state;
+
+    TPMRecvDataCB *recv_data_callback;
+    TPMBackend *tb;
+} TPMPassthruThreadParams;
+
+struct TPMPassthruState {
+    QemuThread thread;
+    bool thread_terminate;
+    bool thread_running;
+
+    TPMPassthruThreadParams tpm_thread_params;
+
+    char tpm_dev[64];
+    int tpm_fd;
+    bool had_startup_error;
+};
+
+#define TPM_PASSTHROUGH_DEFAULT_DEVICE "/dev/tpm0"
+
+/* borrowed from qemu-char.c */
+static int tpm_passthrough_unix_write(int fd, const uint8_t *buf, uint32_t len)
+{
+    int ret, len1;
+
+    len1 = len;
+    while (len1 > 0) {
+        ret = write(fd, buf, len1);
+        if (ret < 0) {
+            if (errno != EINTR && errno != EAGAIN) {
+                return -1;
+            }
+        } else if (ret == 0) {
+            break;
+        } else {
+            buf  += ret;
+            len1 -= ret;
+        }
+    }
+    return len - len1;
+}
+
+static int tpm_passthrough_unix_read(int fd, uint8_t *buf, uint32_t len)
+{
+    int ret, len1;
+    uint8_t *buf1;
+
+    len1 = len;
+    buf1 = buf;
+    while ((len1 > 0) && (ret = read(fd, buf1, len1)) != 0) {
+        if (ret < 0) {
+            if (errno != EINTR && errno != EAGAIN) {
+                return -1;
+            }
+        } else {
+            buf1 += ret;
+            len1 -= ret;
+        }
+    }
+    return len - len1;
+}
+
+static void *tpm_passthrough_main_loop(void *d)
+{
+    TPMPassthruThreadParams *thr_parms = d;
+    TPMPassthruState *tpm_pt = thr_parms->tb->s.tpm_pt;
+    uint32_t in_len, out_len;
+    uint8_t *in, *out;
+    uint8_t locty;
+    TPMLocality *cmd_locty;
+    int ret;
+
+#ifdef DEBUG_TPM
+    fprintf(stderr, "tpm_passthrough: THREAD IS STARTING\n");
+#endif
+
+    /* start command processing */
+    while (!tpm_pt->thread_terminate) {
+        /* receive and handle commands */
+        in_len = 0;
+        do {
+#ifdef DEBUG_TPM
+            fprintf(stderr, "tpm_passthrough: waiting for commands...\n");
+#endif
+
+            if (tpm_pt->thread_terminate) {
+                break;
+            }
+
+            qemu_mutex_lock(&thr_parms->tpm_state->state_lock);
+
+            /* in case we were to slow and missed the signal, the
+               to_tpm_execute boolean tells us about a pending command */
+            if (!thr_parms->tpm_state->to_tpm_execute) {
+                qemu_cond_wait(&thr_parms->tpm_state->to_tpm_cond,
+                        &thr_parms->tpm_state->state_lock);
+            }
+
+            thr_parms->tpm_state->to_tpm_execute = false;
+
+            qemu_mutex_unlock(&thr_parms->tpm_state->state_lock);
+
+            if (tpm_pt->thread_terminate) {
+                break;
+            }
+
+            locty = thr_parms->tpm_state->command_locty;
+
+            cmd_locty = thr_parms->tpm_state->cmd_locty;
+
+            in      = cmd_locty->w_buffer.buffer;
+            in_len  = cmd_locty->w_offset;
+            out     = cmd_locty->r_buffer.buffer;
+            out_len = cmd_locty->r_buffer.size;
+
+            ret = tpm_passthrough_unix_write(tpm_pt->tpm_fd, in, in_len);
+            if (ret < 0) {
+                error_report("tpm_passthrough: error while transmitting data "
+                             "to host tpm: %s (%i)\n",
+                             strerror(errno), errno);
+                tpm_write_std_fatal_error_response(out, out_len, in, in_len);
+                goto send_resp;
+            }
+
+            ret = tpm_passthrough_unix_read(tpm_pt->tpm_fd, out, out_len);
+            if (ret < 0) {
+                error_report("tpm_passthrough: error while reading data from "
+                             "host tpm : %s (%i)\n",
+                             strerror(errno), errno);
+                tpm_write_std_fatal_error_response(out, out_len, in, in_len);
+            }
+
+send_resp:
+            thr_parms->recv_data_callback(thr_parms->tpm_state, locty);
+        } while (in_len > 0);
+    }
+
+#ifdef DEBUG_TPM
+    fprintf(stderr, "tpm_passthrough: THREAD IS ENDING\n");
+#endif
+
+    tpm_pt->thread_running = false;
+
+    return NULL;
+}
+
+static void tpm_passthrough_terminate_tpm_thread(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+    if (!tpm_pt->thread_running) {
+        return;
+    }
+
+#if defined DEBUG_TPM
+    fprintf(stderr, "tpm_passthrough: TERMINATING RUNNING TPM THREAD\n");
+#endif
+
+    if (!tpm_pt->thread_terminate) {
+        tpm_pt->thread_terminate = true;
+
+        qemu_mutex_lock(&tpm_pt->tpm_thread_params.tpm_state->state_lock);
+        qemu_cond_signal(&tpm_pt->tpm_thread_params.tpm_state->to_tpm_cond);
+        qemu_mutex_unlock(&tpm_pt->tpm_thread_params.tpm_state->state_lock);
+
+        while (tpm_pt->thread_running) {
+            usleep(100000);
+        }
+        memset(&tpm_pt->thread, 0, sizeof(tpm_pt->thread));
+    }
+}
+
+/**
+ * Start the TPM (thread). If it had been started before, then terminate
+ * and start it again.
+ */
+static int tpm_passthrough_do_startup_tpm(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+    /* terminate a running TPM */
+    tpm_passthrough_terminate_tpm_thread(tb);
+
+    /* reset the flag so the thread keeps on running */
+    tpm_pt->thread_terminate = false;
+
+    qemu_thread_create(&tpm_pt->thread, tpm_passthrough_main_loop,
+                       &tpm_pt->tpm_thread_params);
+
+    tpm_pt->thread_running = true;
+
+    return 0;
+}
+
+static int tpm_passthrough_startup_tpm(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+    int rc;
+
+    rc = tpm_passthrough_do_startup_tpm(tb);
+    if (rc) {
+        tpm_pt->had_startup_error = true;
+    }
+    return rc;
+}
+
+static void tpm_passthrough_reset(TPMBackend *tb)
+{
+    TPMPassthruState *tpm_pt = tb->s.tpm_pt;
+
+#if defined DEBUG_TPM
+    fprintf(stderr, "tpm_passthrough: CALL TO TPM_RESET!\n");
+#endif
+
+    tpm_passthrough_terminate_tpm_thread(tb);
+
+    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;
+
+    tpm_pt->thread_running = false;
+
+    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);
+        if (sb->buffer != NULL) {
+            sb->size = wanted_size;
+        } else {
+            sb->size = 0;
+        }
+    }
+    return sb->size;
+}
+
+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;
+    char buf[64];
+    int n;
+
+    value = qemu_opt_get(opts, "path");
+    if (!value) {
+        value = TPM_PASSTHROUGH_DEFAULT_DEVICE;
+    }
+
+    n = snprintf(tb->s.tpm_pt->tpm_dev, sizeof(tb->s.tpm_pt->tpm_dev),
+                 "%s", value);
+
+    if (n >= sizeof(tb->s.tpm_pt->tpm_dev)) {
+        error_report("TPM device path is too long.\n");
+        goto err_exit;
+    }
+
+    snprintf(buf, sizeof(buf), "path=%s", tb->s.tpm_pt->tpm_dev);
+
+    tb->parameters = g_strdup(buf);
+
+    if (tb->parameters == NULL) {
+        return 1;
+    }
+
+    tb->s.tpm_pt->tpm_fd = 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'.\n",
+                     tb->s.tpm_pt->tpm_dev);
+        goto err_exit;
+    }
+
+    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:
+    close(tb->s.tpm_pt->tpm_fd);
+    tb->s.tpm_pt->tpm_fd = -1;
+
+ err_exit:
+    g_free(tb->parameters);
+    tb->parameters = NULL;
+
+    return 1;
+}
+
+
+static TPMBackend *tpm_passthrough_create(QemuOpts *opts, const char *id)
+{
+    TPMBackend *tb;
+
+    tb = g_malloc0(sizeof(TPMBackend));
+    if (tb == NULL) {
+        error_report("tpm_passthrough: Could not allocate memory.\n");
+        return NULL;
+    }
+
+    tb->s.tpm_pt = g_malloc0(sizeof(TPMPassthruState));
+    if (tb->s.tpm_pt == NULL) {
+        error_report("tpm_passthrough: Could not allocate memory.\n");
+        g_free(tb);
+        return NULL;
+    }
+
+    tb->id = g_strdup(id);
+    if (tb->id == NULL) {
+        error_report("tpm_passthrough: Could not allocate memory.\n");
+        goto err_exit;
+    }
+
+    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_passthrough_terminate_tpm_thread(tb);
+
+    close(tpm_pt->tpm_fd);
+
+    g_free(tb->id);
+    g_free(tb->parameters);
+    g_free(tb->s.tpm_pt);
+    g_free(tb);
+}
+
+const TPMDriverOps tpm_passthrough_driver = {
+    .id                       = "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,
+    .get_tpm_established_flag = tpm_passthrough_get_tpm_established_flag,
+};
Index: qemu-git.pt/qemu-options.hx
===================================================================
--- qemu-git.pt.orig/qemu-options.hx
+++ qemu-git.pt/qemu-options.hx
@@ -1777,6 +1777,7 @@ The general form of a TPM device option 
 @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} options requires a @code{-device} option.
@@ -1788,6 +1789,38 @@ Use ? to print all available TPM backend
 qemu -tpmdev ?
 @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
Index: qemu-git.pt/tpm.c
===================================================================
--- qemu-git.pt.orig/tpm.c
+++ qemu-git.pt/tpm.c
@@ -18,12 +18,35 @@
 #include "qerror.h"
 
 static const TPMDriverOps *bes[] = {
+#ifdef CONFIG_TPM_PASSTHROUGH
+    &tpm_passthrough_driver,
+#endif
     NULL,
 };
 
 static QLIST_HEAD(, TPMBackend) tpm_backends =
     QLIST_HEAD_INITIALIZER(tpm_backends);
 
+void tpm_write_std_fatal_error_response(uint8_t *out, uint32_t out_len,
+                                        uint8_t *in, uint32_t in_len)
+{
+    if (out_len > sizeof(struct tpm_resp_hdr)) {
+        struct tpm_resp_hdr *resp = (struct tpm_resp_hdr *)out;
+        struct tpm_req_hdr *req  = (struct tpm_req_hdr *)in;
+        uint16_t tag = be16_to_cpu(req->tag);
+
+        resp->tag = cpu_to_be16(
+                     (in_len > 2 &&
+                      tag >= TPM_TAG_RQU_COMMAND &&
+                      tag <= TPM_TAG_RQU_AUTH2_COMMAND)
+                     ? tag + 3
+                     : 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 *id)
 {
     int i;
Index: qemu-git.pt/tpm.h
===================================================================
--- qemu-git.pt.orig/tpm.h
+++ qemu-git.pt/tpm.h
@@ -7,12 +7,18 @@
 struct TPMDriverOps;
 typedef struct TPMDriverOps TPMDriverOps;
 
+typedef struct TPMPassthruState TPMPassthruState;
+
 typedef struct TPMBackend {
     char *id;
     const char *fe_model;
     char *parameters;
     const TPMDriverOps *ops;
 
+    union {
+        TPMPassthruState *tpm_pt;
+    } s;
+
     QLIST_ENTRY(TPMBackend) list;
 } TPMBackend;
 
@@ -79,6 +85,30 @@ static inline void tpm_dump_buffer(FILE 
 
 #define TPM_DEFAULT_DEVICE_MODEL "tpm-tis"
 
+struct tpm_req_hdr {
+    uint16_t tag;
+    uint32_t len;
+    uint32_t ordinal;
+} __attribute__((packed));
+
+struct tpm_resp_hdr {
+    uint16_t tag;
+    uint32_t len;
+    uint32_t errcode;
+} __attribute__((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
+
 void tpm_config_parse(QemuOptsList *opts_list, const char *optarg);
 int tpm_init(void);
 void tpm_cleanup(void);
@@ -86,5 +116,9 @@ TPMBackend *qemu_find_tpm(const char *id
 void do_info_tpm(Monitor *mon);
 void tpm_display_backend_drivers(void);
 const TPMDriverOps *tpm_get_backend_driver(const char *id);
+void tpm_write_std_fatal_error_response(uint8_t *out, uint32_t out_len,
+                                        uint8_t *in, uint32_t in_len);
+
+extern const TPMDriverOps tpm_passthrough_driver;
 
 #endif /* _QEMU_TPM_H */