Patchwork [V19,7/7] Add fd parameter for TPM passthrough driver

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Submitter Stefan Berger
Date June 4, 2012, 7:37 p.m.
Message ID <1338838668-7544-8-git-send-email-stefanb@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/162863/
State New
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Comments

Stefan Berger - June 4, 2012, 7:37 p.m.
Enable the passing of a file descriptor via fd=<..> to access the host's
TPM device using the TPM passthrough driver.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
---
 hmp.c                |    7 +++++-
 hw/tpm_passthrough.c |   53 ++++++++++++++++++++++++++++++++++++++-----------
 qapi-schema.json     |    4 ++-
 qemu-config.c        |    5 ++++
 qemu-options.hx      |   11 +++++++--
 tpm.c                |    4 +++
 tpm.h                |    1 +
 7 files changed, 68 insertions(+), 17 deletions(-)
Corey Bryant - Sept. 27, 2012, 2:35 p.m.
On 06/04/2012 03:37 PM, Stefan Berger wrote:
> Enable the passing of a file descriptor via fd=<..> to access the host's
> TPM device using the TPM passthrough driver.
>
> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
> ---
>   hmp.c                |    7 +++++-
>   hw/tpm_passthrough.c |   53 ++++++++++++++++++++++++++++++++++++++-----------
>   qapi-schema.json     |    4 ++-
>   qemu-config.c        |    5 ++++
>   qemu-options.hx      |   11 +++++++--
>   tpm.c                |    4 +++
>   tpm.h                |    1 +
>   7 files changed, 68 insertions(+), 17 deletions(-)
>
> diff --git a/hmp.c b/hmp.c
> index 9aedaff..3176c74 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -567,10 +567,15 @@ void hmp_info_tpm(Monitor *mon)
>           TPMInfo *ti = info->value;
>           monitor_printf(mon, " tpm%d: model=%s\n",
>                          c, ti->model);
> -        monitor_printf(mon, "  \\ %s: type=%s%s%s\n",
> +        monitor_printf(mon, "  \\ %s: type=%s%s%s",
>                          ti->id, ti->type,
>                          ti->has_path ? ",path=" : "",
>                          ti->has_path ? ti->path : "");
> +        if (ti->has_fd) {
> +            monitor_printf(mon, ",fd=%" PRId64,
> +                           ti->fd);
> +        }
> +        monitor_printf(mon, "\n");
>           c++;
>       }
>       qapi_free_TPMInfoList(info_list);
> diff --git a/hw/tpm_passthrough.c b/hw/tpm_passthrough.c
> index 8914705..44cf272 100644
> --- a/hw/tpm_passthrough.c
> +++ b/hw/tpm_passthrough.c
> @@ -305,26 +305,54 @@ static int tpm_passthrough_test_tpmdev(int fd)
>   static int tpm_passthrough_handle_device_opts(QemuOpts *opts, TPMBackend *tb)
>   {
>       const char *value;
> +    struct stat statbuf;
>
> -    value = qemu_opt_get(opts, "path");
> -    if (!value) {
> -        value = TPM_PASSTHROUGH_DEFAULT_DEVICE;
> -    }
> +    value = qemu_opt_get(opts, "fd");
> +    if (value) {
> +        if (qemu_opt_get(opts, "path")) {
> +            error_report("fd= is invalid with path=");
> +            goto err_exit;
> +        }
> +
> +        tb->s.tpm_pt->tpm_fd = qemu_parse_fd(value);
> +        if (tb->s.tpm_pt->tpm_fd < 0) {
> +            error_report("Illegal file descriptor for TPM device.\n");
> +            goto err_exit;
> +        }
> +
> +        tb->tpm_fd = &tb->s.tpm_pt->tpm_fd;
> +    } else {
> +        value = qemu_opt_get(opts, "path");
> +        if (!value) {
> +            value = TPM_PASSTHROUGH_DEFAULT_DEVICE;
> +        }
>
> -    tb->s.tpm_pt->tpm_dev = g_strdup(value);
> +        tb->s.tpm_pt->tpm_dev = g_strdup(value);
>
> -    tb->path = g_strdup(tb->s.tpm_pt->tpm_dev);
> +        tb->path = g_strdup(value);
> +
> +        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_free_parameters;
> +        }
> +    }
> +
> +    if (fstat(tb->s.tpm_pt->tpm_fd, &statbuf) != 0) {
> +        error_report("Cannot determine file descriptor type for TPM "
> +                     "device: %s", strerror(errno));
> +        goto err_close_tpmdev;
> +    }
>
> -    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);
> +    /* only allow character devices for now */
> +    if (!S_ISCHR(statbuf.st_mode)) {
> +        error_report("TPM file descriptor is not a character device");
>           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);
> +        error_report("Device is not a TPM.\n");
>           goto err_close_tpmdev;
>       }
>
> @@ -341,6 +369,7 @@ static int tpm_passthrough_handle_device_opts(QemuOpts *opts, TPMBackend *tb)
>       g_free(tb->s.tpm_pt->tpm_dev);
>       tb->s.tpm_pt->tpm_dev = NULL;
>
> + err_exit:
>       return 1;
>   }
>
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 8799322..9d6f664 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1769,10 +1769,12 @@
>   #
>   # @path: #optional Path to the TPM backend device
>   #
> +# @fd: #optional File descriptor for the TPM backend device
>   # Since: 1.1
>   ##
>   { 'type': 'TPMInfo',
> -  'data': {'model': 'str', 'id': 'str', 'type': 'str', '*path': 'str' } }
> +  'data': {'model': 'str', 'id': 'str', 'type': 'str', '*path': 'str',
> +           '*fd' : 'int' } }
>
>   ##
>   # @query-tpm
> diff --git a/qemu-config.c b/qemu-config.c
> index edc8d5d..a5e2677 100644
> --- a/qemu-config.c
> +++ b/qemu-config.c
> @@ -628,6 +628,11 @@ static QemuOptsList qemu_tpmdev_opts = {
>               .type = QEMU_OPT_STRING,
>               .help = "Persistent storage for TPM state",
>           },
> +        {
> +            .name = "fd",
> +            .type = QEMU_OPT_STRING,
> +            .help = "Filedescriptor for accessing the TPM",
> +        },
>           { /* end of list */ }
>       },
>   };
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 0b9fa0b..cb9892b 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -2017,8 +2017,9 @@ DEFHEADING()
>   DEFHEADING(TPM device options:)
>
>   DEF("tpmdev", HAS_ARG, QEMU_OPTION_tpmdev, \
> -    "-tpmdev passthrough,id=id[,path=path]\n"
> -    "                use path to provide path to a character device; default is /dev/tpm0\n",
> +    "-tpmdev passthrough,id=id[,path=path][,fd=h]\n"
> +    "                use path to provide path to a character device; default is /dev/tpm0\n"
> +    "                use fd to provide a file descriptor to a character device\n",
>       QEMU_ARCH_ALL)
>   STEXI
>
> @@ -2040,7 +2041,7 @@ Use ? to print all available TPM backend types.
>   qemu -tpmdev ?
>   @end example
>
> -@item -tpmdev passthrough, id=@var{id}, path=@var{path}
> +@item -tpmdev passthrough, id=@var{id}, path=@var{path}, fd=@var{h}
>
>   (Linux-host only) Enable access to the host's TPM using the passthrough
>   driver.
> @@ -2049,6 +2050,10 @@ driver.
>   a Linux host this would be @code{/dev/tpm0}.
>   @option{path} is optional and by default @code{/dev/tpm0} is used.
>
> +@option{fd} specifies the file descriptor of the host's TPM device.
> +@option{fd} and @option{path} are mutually exclusive.
> +@option{fd} is optional.
> +
>   Some notes about using the host's TPM with the passthrough driver:
>
>   The TPM device accessed by the passthrough driver must not be
> diff --git a/tpm.c b/tpm.c
> index 79530c9..64d3140 100644
> --- a/tpm.c
> +++ b/tpm.c
> @@ -201,6 +201,10 @@ static TPMInfo *qmp_query_tpm_inst(TPMBackend *drv)
>           res->path = g_strdup(drv->path);
>           res->has_path = true;
>       }
> +    if (drv->tpm_fd != NULL && *drv->tpm_fd >= 0) {
> +        res->fd = *drv->tpm_fd;
> +        res->has_fd = true;
> +    }
>       res->type = g_strdup(drv->ops->id);
>
>       return res;
> diff --git a/tpm.h b/tpm.h
> index bacaff3..00f7600 100644
> --- a/tpm.h
> +++ b/tpm.h
> @@ -24,6 +24,7 @@ typedef struct TPMBackend {
>       char *id;
>       const char *fe_model;
>       char *path;
> +    int  *tpm_fd;
>       const TPMDriverOps *ops;
>
>       union {
>

This patch looks okay to me.
Corey Bryant - Oct. 3, 2012, 6:46 p.m.
On 06/04/2012 03:37 PM, Stefan Berger wrote:
> Enable the passing of a file descriptor via fd=<..> to access the host's
> TPM device using the TPM passthrough driver.
>
> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
> ---
>   hmp.c                |    7 +++++-
>   hw/tpm_passthrough.c |   53 ++++++++++++++++++++++++++++++++++++++-----------
>   qapi-schema.json     |    4 ++-
>   qemu-config.c        |    5 ++++
>   qemu-options.hx      |   11 +++++++--
>   tpm.c                |    4 +++
>   tpm.h                |    1 +
>   7 files changed, 68 insertions(+), 17 deletions(-)
>
> diff --git a/hmp.c b/hmp.c
> index 9aedaff..3176c74 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -567,10 +567,15 @@ void hmp_info_tpm(Monitor *mon)
>           TPMInfo *ti = info->value;
>           monitor_printf(mon, " tpm%d: model=%s\n",
>                          c, ti->model);
> -        monitor_printf(mon, "  \\ %s: type=%s%s%s\n",
> +        monitor_printf(mon, "  \\ %s: type=%s%s%s",
>                          ti->id, ti->type,
>                          ti->has_path ? ",path=" : "",
>                          ti->has_path ? ti->path : "");
> +        if (ti->has_fd) {
> +            monitor_printf(mon, ",fd=%" PRId64,
> +                           ti->fd);
> +        }
> +        monitor_printf(mon, "\n");
>           c++;
>       }
>       qapi_free_TPMInfoList(info_list);
> diff --git a/hw/tpm_passthrough.c b/hw/tpm_passthrough.c
> index 8914705..44cf272 100644
> --- a/hw/tpm_passthrough.c
> +++ b/hw/tpm_passthrough.c
> @@ -305,26 +305,54 @@ static int tpm_passthrough_test_tpmdev(int fd)
>   static int tpm_passthrough_handle_device_opts(QemuOpts *opts, TPMBackend *tb)
>   {
>       const char *value;
> +    struct stat statbuf;
>
> -    value = qemu_opt_get(opts, "path");
> -    if (!value) {
> -        value = TPM_PASSTHROUGH_DEFAULT_DEVICE;
> -    }
> +    value = qemu_opt_get(opts, "fd");
> +    if (value) {
> +        if (qemu_opt_get(opts, "path")) {
> +            error_report("fd= is invalid with path=");
> +            goto err_exit;
> +        }
> +
> +        tb->s.tpm_pt->tpm_fd = qemu_parse_fd(value);
> +        if (tb->s.tpm_pt->tpm_fd < 0) {
> +            error_report("Illegal file descriptor for TPM device.\n");
> +            goto err_exit;
> +        }
> +
> +        tb->tpm_fd = &tb->s.tpm_pt->tpm_fd;
> +    } else {
> +        value = qemu_opt_get(opts, "path");
> +        if (!value) {
> +            value = TPM_PASSTHROUGH_DEFAULT_DEVICE;
> +        }
>
> -    tb->s.tpm_pt->tpm_dev = g_strdup(value);
> +        tb->s.tpm_pt->tpm_dev = g_strdup(value);
>
> -    tb->path = g_strdup(tb->s.tpm_pt->tpm_dev);
> +        tb->path = g_strdup(value);
> +
> +        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_free_parameters;
> +        }
> +    }
> +
> +    if (fstat(tb->s.tpm_pt->tpm_fd, &statbuf) != 0) {
> +        error_report("Cannot determine file descriptor type for TPM "
> +                     "device: %s", strerror(errno));
> +        goto err_close_tpmdev;
> +    }
>
> -    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);
> +    /* only allow character devices for now */
> +    if (!S_ISCHR(statbuf.st_mode)) {
> +        error_report("TPM file descriptor is not a character device");
>           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);
> +        error_report("Device is not a TPM.\n");
>           goto err_close_tpmdev;
>       }
>
> @@ -341,6 +369,7 @@ static int tpm_passthrough_handle_device_opts(QemuOpts *opts, TPMBackend *tb)
>       g_free(tb->s.tpm_pt->tpm_dev);
>       tb->s.tpm_pt->tpm_dev = NULL;
>
> + err_exit:
>       return 1;
>   }
>
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 8799322..9d6f664 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1769,10 +1769,12 @@
>   #
>   # @path: #optional Path to the TPM backend device
>   #
> +# @fd: #optional File descriptor for the TPM backend device
>   # Since: 1.1
>   ##
>   { 'type': 'TPMInfo',
> -  'data': {'model': 'str', 'id': 'str', 'type': 'str', '*path': 'str' } }
> +  'data': {'model': 'str', 'id': 'str', 'type': 'str', '*path': 'str',
> +           '*fd' : 'int' } }
>
>   ##
>   # @query-tpm
> diff --git a/qemu-config.c b/qemu-config.c
> index edc8d5d..a5e2677 100644
> --- a/qemu-config.c
> +++ b/qemu-config.c
> @@ -628,6 +628,11 @@ static QemuOptsList qemu_tpmdev_opts = {
>               .type = QEMU_OPT_STRING,
>               .help = "Persistent storage for TPM state",
>           },
> +        {
> +            .name = "fd",
> +            .type = QEMU_OPT_STRING,
> +            .help = "Filedescriptor for accessing the TPM",

Filedescriptor needs a space.

> +        },
>           { /* end of list */ }
>       },
>   };
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 0b9fa0b..cb9892b 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -2017,8 +2017,9 @@ DEFHEADING()
>   DEFHEADING(TPM device options:)
>
>   DEF("tpmdev", HAS_ARG, QEMU_OPTION_tpmdev, \
> -    "-tpmdev passthrough,id=id[,path=path]\n"
> -    "                use path to provide path to a character device; default is /dev/tpm0\n",
> +    "-tpmdev passthrough,id=id[,path=path][,fd=h]\n"
> +    "                use path to provide path to a character device; default is /dev/tpm0\n"
> +    "                use fd to provide a file descriptor to a character device\n",
>       QEMU_ARCH_ALL)
>   STEXI
>
> @@ -2040,7 +2041,7 @@ Use ? to print all available TPM backend types.
>   qemu -tpmdev ?
>   @end example
>
> -@item -tpmdev passthrough, id=@var{id}, path=@var{path}
> +@item -tpmdev passthrough, id=@var{id}, path=@var{path}, fd=@var{h}
>
>   (Linux-host only) Enable access to the host's TPM using the passthrough
>   driver.
> @@ -2049,6 +2050,10 @@ driver.
>   a Linux host this would be @code{/dev/tpm0}.
>   @option{path} is optional and by default @code{/dev/tpm0} is used.
>
> +@option{fd} specifies the file descriptor of the host's TPM device.
> +@option{fd} and @option{path} are mutually exclusive.
> +@option{fd} is optional.
> +
>   Some notes about using the host's TPM with the passthrough driver:
>
>   The TPM device accessed by the passthrough driver must not be
> diff --git a/tpm.c b/tpm.c
> index 79530c9..64d3140 100644
> --- a/tpm.c
> +++ b/tpm.c
> @@ -201,6 +201,10 @@ static TPMInfo *qmp_query_tpm_inst(TPMBackend *drv)
>           res->path = g_strdup(drv->path);
>           res->has_path = true;
>       }
> +    if (drv->tpm_fd != NULL && *drv->tpm_fd >= 0) {
> +        res->fd = *drv->tpm_fd;
> +        res->has_fd = true;
> +    }

Is an else path needed to set res->has_fd = false if there's no tpm_fd?
Stefan Berger - Oct. 24, 2012, 7:06 p.m.
On 10/03/2012 02:46 PM, Corey Bryant wrote:
>
>
> On 06/04/2012 03:37 PM, Stefan Berger wrote:
>> @@ -201,6 +201,10 @@ static TPMInfo *qmp_query_tpm_inst(TPMBackend *drv)
>>           res->path = g_strdup(drv->path);
>>           res->has_path = true;
>>       }
>> +    if (drv->tpm_fd != NULL && *drv->tpm_fd >= 0) {
>> +        res->fd = *drv->tpm_fd;
>> +        res->has_fd = true;
>> +    }
>
> Is an else path needed to set res->has_fd = false if there's no tpm_fd?
>

res is allocated using g_new0, so all fields are set to 0. With that 
has_fd is also set to false.

Regards,
    Stefan

Patch

diff --git a/hmp.c b/hmp.c
index 9aedaff..3176c74 100644
--- a/hmp.c
+++ b/hmp.c
@@ -567,10 +567,15 @@  void hmp_info_tpm(Monitor *mon)
         TPMInfo *ti = info->value;
         monitor_printf(mon, " tpm%d: model=%s\n",
                        c, ti->model);
-        monitor_printf(mon, "  \\ %s: type=%s%s%s\n",
+        monitor_printf(mon, "  \\ %s: type=%s%s%s",
                        ti->id, ti->type,
                        ti->has_path ? ",path=" : "",
                        ti->has_path ? ti->path : "");
+        if (ti->has_fd) {
+            monitor_printf(mon, ",fd=%" PRId64,
+                           ti->fd);
+        }
+        monitor_printf(mon, "\n");
         c++;
     }
     qapi_free_TPMInfoList(info_list);
diff --git a/hw/tpm_passthrough.c b/hw/tpm_passthrough.c
index 8914705..44cf272 100644
--- a/hw/tpm_passthrough.c
+++ b/hw/tpm_passthrough.c
@@ -305,26 +305,54 @@  static int tpm_passthrough_test_tpmdev(int fd)
 static int tpm_passthrough_handle_device_opts(QemuOpts *opts, TPMBackend *tb)
 {
     const char *value;
+    struct stat statbuf;
 
-    value = qemu_opt_get(opts, "path");
-    if (!value) {
-        value = TPM_PASSTHROUGH_DEFAULT_DEVICE;
-    }
+    value = qemu_opt_get(opts, "fd");
+    if (value) {
+        if (qemu_opt_get(opts, "path")) {
+            error_report("fd= is invalid with path=");
+            goto err_exit;
+        }
+
+        tb->s.tpm_pt->tpm_fd = qemu_parse_fd(value);
+        if (tb->s.tpm_pt->tpm_fd < 0) {
+            error_report("Illegal file descriptor for TPM device.\n");
+            goto err_exit;
+        }
+
+        tb->tpm_fd = &tb->s.tpm_pt->tpm_fd;
+    } else {
+        value = qemu_opt_get(opts, "path");
+        if (!value) {
+            value = TPM_PASSTHROUGH_DEFAULT_DEVICE;
+        }
 
-    tb->s.tpm_pt->tpm_dev = g_strdup(value);
+        tb->s.tpm_pt->tpm_dev = g_strdup(value);
 
-    tb->path = g_strdup(tb->s.tpm_pt->tpm_dev);
+        tb->path = g_strdup(value);
+
+        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_free_parameters;
+        }
+    }
+
+    if (fstat(tb->s.tpm_pt->tpm_fd, &statbuf) != 0) {
+        error_report("Cannot determine file descriptor type for TPM "
+                     "device: %s", strerror(errno));
+        goto err_close_tpmdev;
+    }
 
-    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);
+    /* only allow character devices for now */
+    if (!S_ISCHR(statbuf.st_mode)) {
+        error_report("TPM file descriptor is not a character device");
         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);
+        error_report("Device is not a TPM.\n");
         goto err_close_tpmdev;
     }
 
@@ -341,6 +369,7 @@  static int tpm_passthrough_handle_device_opts(QemuOpts *opts, TPMBackend *tb)
     g_free(tb->s.tpm_pt->tpm_dev);
     tb->s.tpm_pt->tpm_dev = NULL;
 
+ err_exit:
     return 1;
 }
 
diff --git a/qapi-schema.json b/qapi-schema.json
index 8799322..9d6f664 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1769,10 +1769,12 @@ 
 #
 # @path: #optional Path to the TPM backend device
 #
+# @fd: #optional File descriptor for the TPM backend device
 # Since: 1.1
 ##
 { 'type': 'TPMInfo',
-  'data': {'model': 'str', 'id': 'str', 'type': 'str', '*path': 'str' } }
+  'data': {'model': 'str', 'id': 'str', 'type': 'str', '*path': 'str',
+           '*fd' : 'int' } }
 
 ##
 # @query-tpm
diff --git a/qemu-config.c b/qemu-config.c
index edc8d5d..a5e2677 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -628,6 +628,11 @@  static QemuOptsList qemu_tpmdev_opts = {
             .type = QEMU_OPT_STRING,
             .help = "Persistent storage for TPM state",
         },
+        {
+            .name = "fd",
+            .type = QEMU_OPT_STRING,
+            .help = "Filedescriptor for accessing the TPM",
+        },
         { /* end of list */ }
     },
 };
diff --git a/qemu-options.hx b/qemu-options.hx
index 0b9fa0b..cb9892b 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2017,8 +2017,9 @@  DEFHEADING()
 DEFHEADING(TPM device options:)
 
 DEF("tpmdev", HAS_ARG, QEMU_OPTION_tpmdev, \
-    "-tpmdev passthrough,id=id[,path=path]\n"
-    "                use path to provide path to a character device; default is /dev/tpm0\n",
+    "-tpmdev passthrough,id=id[,path=path][,fd=h]\n"
+    "                use path to provide path to a character device; default is /dev/tpm0\n"
+    "                use fd to provide a file descriptor to a character device\n",
     QEMU_ARCH_ALL)
 STEXI
 
@@ -2040,7 +2041,7 @@  Use ? to print all available TPM backend types.
 qemu -tpmdev ?
 @end example
 
-@item -tpmdev passthrough, id=@var{id}, path=@var{path}
+@item -tpmdev passthrough, id=@var{id}, path=@var{path}, fd=@var{h}
 
 (Linux-host only) Enable access to the host's TPM using the passthrough
 driver.
@@ -2049,6 +2050,10 @@  driver.
 a Linux host this would be @code{/dev/tpm0}.
 @option{path} is optional and by default @code{/dev/tpm0} is used.
 
+@option{fd} specifies the file descriptor of the host's TPM device.
+@option{fd} and @option{path} are mutually exclusive.
+@option{fd} is optional.
+
 Some notes about using the host's TPM with the passthrough driver:
 
 The TPM device accessed by the passthrough driver must not be
diff --git a/tpm.c b/tpm.c
index 79530c9..64d3140 100644
--- a/tpm.c
+++ b/tpm.c
@@ -201,6 +201,10 @@  static TPMInfo *qmp_query_tpm_inst(TPMBackend *drv)
         res->path = g_strdup(drv->path);
         res->has_path = true;
     }
+    if (drv->tpm_fd != NULL && *drv->tpm_fd >= 0) {
+        res->fd = *drv->tpm_fd;
+        res->has_fd = true;
+    }
     res->type = g_strdup(drv->ops->id);
 
     return res;
diff --git a/tpm.h b/tpm.h
index bacaff3..00f7600 100644
--- a/tpm.h
+++ b/tpm.h
@@ -24,6 +24,7 @@  typedef struct TPMBackend {
     char *id;
     const char *fe_model;
     char *path;
+    int  *tpm_fd;
     const TPMDriverOps *ops;
 
     union {