[Qemu-devel] [PATCH V13 7/7] 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>

---

v13:
 - Only accepting a character device's file descriptor

v12:
 - added documentation part
---
 hw/tpm_passthrough.c |   73 +++++++++++++++++++++++++++++++++++++-------------
 qemu-config.c        |    5 +++
 qemu-options.hx      |    6 +++-
 3 files changed, 64 insertions(+), 20 deletions(-)

diff --git a/hw/tpm_passthrough.c b/hw/tpm_passthrough.c
index f9cfe3d..57bb77a 100644
--- a/hw/tpm_passthrough.c
+++ b/hw/tpm_passthrough.c
@@ -361,33 +361,68 @@ static int tpm_passthrough_handle_device_opts(QemuOpts *opts, TPMBackend *tb)
     const char *value;
     char buf[64];
     int n;
+    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=");
+            return -1;
+        }
+
+        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");
+            return -1;
+        }
 
-    n = snprintf(tb->s.tpm_pt->tpm_dev, sizeof(tb->s.tpm_pt->tpm_dev),
-                 "%s", value);
+        snprintf(buf, sizeof(buf), "fd=%d", tb->s.tpm_pt->tpm_fd);
 
-    if (n >= sizeof(tb->s.tpm_pt->tpm_dev)) {
-        error_report("TPM device path is too long.\n");
-        goto err_exit;
-    }
+        tb->parameters = g_strdup(buf);
 
-    snprintf(buf, sizeof(buf), "path=%s", tb->s.tpm_pt->tpm_dev);
+        if (tb->parameters == NULL) {
+            goto err_close_tpmdev;
+        }
+    } else {
+        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;
+        }
 
-    tb->parameters = g_strdup(buf);
+        snprintf(buf, sizeof(buf), "path=%s", tb->s.tpm_pt->tpm_dev);
 
-    if (tb->parameters == NULL) {
-        return 1;
+        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;
+        }
     }
 
-    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 (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;
+    }
+
+    /* only allow character devices for now */
+    if (!S_ISCHR(statbuf.st_mode)) {
+        error_report("TPM file descriptor is not a character device");
+        goto err_close_tpmdev;
     }
 
     if (tpm_passthrough_test_tpmdev(tb->s.tpm_pt->tpm_fd)) {
diff --git a/qemu-config.c b/qemu-config.c
index cc4c31d..e49f4d8 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -564,6 +564,11 @@ 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 4916baf..7eca701 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1932,7 +1932,7 @@ 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.
@@ -1941,6 +1941,10 @@ 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
-- 
1.7.6.4