[Qemu-devel] [PATCH V20 8/8] Add fd parameter for TPM passthrough driver

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

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 8d63d03..ee6ab54 100644
--- a/hmp.c
+++ b/hmp.c
@@ -647,12 +647,17 @@ 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%s%s\n",
+        monitor_printf(mon, "  \\ %s: type=%s%s%s%s%s",
                        ti->id, ti->type,
                        ti->has_path ? ",path=" : "",
                        ti->has_path ? ti->path : "",
                        ti->has_cancel_path ? ",cancel_path=" : "",
                        ti->has_cancel_path ? ti->cancel_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 1b17c30..3843268 100644
--- a/hw/tpm_passthrough.c
+++ b/hw/tpm_passthrough.c
@@ -420,26 +420,54 @@ exit:
 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': %s\n",
+                         tb->s.tpm_pt->tpm_dev, strerror(errno));
+            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': %s\n",
-                     tb->s.tpm_pt->tpm_dev, strerror(errno));
+    /* 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;
     }
 
@@ -456,6 +484,7 @@ 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 82f753b..43b46e7 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -3033,11 +3033,13 @@
 #
 # @cancel_path: #optional Path to TPM backend device's cancel sysfs entry
 #
+# @fd: #optional File descriptor for the TPM backend device
+#
 # Since: 1.5.0
 ##
 { 'type': 'TPMInfo',
   'data': {'model': 'str', 'id': 'str', 'type': 'str', '*path': 'str',
-           '*cancel_path': 'str' } }
+           '*cancel_path': 'str', '*fd' : 'int' } }
 
 ##
 # @query-tpm
diff --git a/qemu-config.c b/qemu-config.c
index 59f605a..e0e1c6f 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -706,6 +706,11 @@ static QemuOptsList qemu_tpmdev_opts = {
             .type = QEMU_OPT_STRING,
             .help = "Persistent storage for TPM state",
         },
+        {
+            .name = "fd",
+            .type = QEMU_OPT_STRING,
+            .help = "File descriptor for accessing the TPM",
+        },
         { /* end of list */ }
     },
 };
diff --git a/qemu-options.hx b/qemu-options.hx
index 225191f..bb7fe44 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2163,8 +2163,9 @@ 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
 
@@ -2186,7 +2187,7 @@ 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.
@@ -2195,6 +2196,10 @@ 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 4730039..5cb9772 100644
--- a/tpm.c
+++ b/tpm.c
@@ -204,6 +204,10 @@ static TPMInfo *qmp_query_tpm_inst(TPMBackend *drv)
         res->cancel_path = g_strdup(drv->cancel_path);
         res->has_cancel_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->type);
 
     return res;
diff --git a/tpm.h b/tpm.h
index b4f7774..7d3dcac 100644
--- a/tpm.h
+++ b/tpm.h
@@ -25,6 +25,7 @@ typedef struct TPMBackend {
     const char *fe_model;
     char *path;
     char *cancel_path;
+    int  *tpm_fd;
     const TPMDriverOps *ops;
 
     union {
-- 
1.7.11.7