[Qemu-devel] [PATCH Appendix] Skeleton backend driver

[Stefan Berger]

It should be possible to recycle a lot of the backend code. So, below is
a skeleton backend driver with all libtpms and block storage
dependencies removed. It compiled, but doesn't work.

In the areas where I know that code needs to be written into, I marked
it with '// !!!'.

Signed-off-by: Stefan Berger <address@hidden>

Index: qemu-git/hw/tpm_be_skeleton.c
===================================================================
--- /dev/null
+++ qemu-git/hw/tpm_be_skeleton.c
@@ -0,0 +1,369 @@
+/*
+ *
+ *  Copyright (c) 2010, 2011 IBM Corporation
+ *  Copyright (c) 2010, 2011 Stefan Berger
+ *
+ * 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 "hw/hw.h"
+#include "hw/tpm_tis.h"
+#include "hw/pc.h"
+
+//#define DEBUG_TPM
+//#define DEBUG_TPM_SR /* suspend - resume */
+
+
+/* data structures */
+
+typedef struct ThreadParams {
+    TPMState *tpm_state;
+
+    TPMRecvDataCB *recv_data_callback;
+} ThreadParams;
+
+
+/* local variables */
+
+static QemuThread thread;
+
+static QemuMutex state_mutex; /* protects *_state below */
+
+static bool thread_terminate = false;
+static bool tpm_initialized = false;
+static bool had_fatal_error = false;
+static bool had_startup_error = false;
+
+static ThreadParams tpm_thread_params;
+
+/* locality of the command being executed by libtpms */
+static uint8_t g_locty;
+
+static const unsigned char tpm_std_fatal_error_response[10] = {
+    0x00, 0xc4, 0x00, 0x00, 0x00, 0x0A, 0x00, 0x00, 0x00, 0x09 /* TPM_FAIL */
+};
+
+static char dev_description[80];
+
+
+/**
+ * Start the TPM. If it had been started before, then terminate and start
+ * it again.
+ */
+static int startup_tpm(void)
+{
+    tpm_initialized = true;
+
+#if defined DEBUG_TPM || defined DEBUG_TPM_SR
+    fprintf(stderr,"tpm: *** tpm startup was successful! ***\n");
+#endif
+
+    return 0;
+}
+
+
+/*
+ * Start up the TPM before it sees the first command.
+ * We need to do this late since only now we will have the
+ * block storage encryption key and can read the previous
+ * TPM state. During 'reset' the key would not be available.
+ */
+static int late_startup_tpm(void)
+{
+    int rc;
+
+    rc  = startup_tpm();
+    if (rc) {
+        had_fatal_error = 1;
+        return 1;
+    }
+
+    return 0;
+}
+
+
+static void terminate_tpm_thread(void)
+{
+    if (!thread_terminate) {
+        thread_terminate = true;
+
+        qemu_mutex_lock  (&tpm_thread_params.tpm_state->state_lock);
+        qemu_cond_signal (&tpm_thread_params.tpm_state->to_tpm_cond);
+        qemu_mutex_unlock(&tpm_thread_params.tpm_state->state_lock);
+
+        qemu_thread_join(&thread, NULL);
+        memset(&thread, 0, sizeof(thread));
+
+        if (tpm_initialized) {
+            tpm_initialized = false;
+        }
+    }
+}
+
+
+static void tpm_atexit(void)
+{
+    terminate_tpm_thread();
+}
+
+
+static void *mainLoop(void *d)
+{
+    int res = 0;
+    ThreadParams *tParams = (ThreadParams *)d;
+    uint32_t in_len, out_len;
+    uint8_t *in, *out;
+    uint32_t resp_size; /* total length of response */
+
+    /* start command processing */
+    while (!thread_terminate) {
+        /* receive and handle commands */
+        in_len = 0;
+        do {
+#ifdef DEBUG_TPM
+            fprintf(stderr,"waiting for commands...\n");
+#endif
+
+            if (thread_terminate)
+                break;
+
+            qemu_mutex_lock(&tParams->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 (!tParams->tpm_state->to_tpm_execute)
+                qemu_cond_wait(&tParams->tpm_state->to_tpm_cond,
+                               &tParams->tpm_state->state_lock);
+
+            tParams->tpm_state->to_tpm_execute = false;
+
+            qemu_mutex_unlock(&tParams->tpm_state->state_lock);
+
+            if (thread_terminate)
+                break;
+
+            g_locty = tParams->tpm_state->command_locty;
+
+            in = tParams->tpm_state->loc[g_locty].w_buffer.buffer;
+            in_len = tParams->tpm_state->loc[g_locty].w_offset;
+
+            if (!had_fatal_error) {
+
+                out_len = tParams->tpm_state->loc[g_locty].r_buffer.size;
+
+#ifdef DEBUG_TPM
+                fprintf(stderr,
+                        "tpm: received %d bytes from VM in locality %d\n",
+                        in_len,
+                        g_locty);
+                dumpBuffer(stdout, in, in_len);
+#endif
+
+                resp_size = 0;
+
+
+                // !!! Send command to TPM & wait for response
+
+
+                if (res != 0) {
+#ifdef DEBUG_TPM
+                    fprintf(stderr,
+                            "Sending/receiving TPM request/response "
+                            "failed\n");
+#endif
+                    had_fatal_error = 1;
+                }
+            }
+
+            if (had_fatal_error) {
+                out = tParams->tpm_state->loc[g_locty].r_buffer.buffer;
+                resp_size = sizeof(tpm_std_fatal_error_response);
+                memcpy(out, tpm_std_fatal_error_response, resp_size);
+                out[1] = (in_len > 2 && in[1] >= 0xc1 && in[1] <= 0xc3)
+                       ? in[1] + 3
+                       : 0xc4;
+            }
+#ifdef DEBUG_TPM
+            fprintf(stderr,"sending %d bytes to VM\n", resp_size);
+            dumpBuffer(stdout, out, resp_size);
+#endif
+            tParams->recv_data_callback(tParams->tpm_state, g_locty);
+        } while (in_len > 0);
+    }
+
+    return NULL;
+}
+
+
+
+/*****************************************************************/
+
+
+static void reset(void)
+{
+    static bool thread_running;
+
+#if defined DEBUG_TPM || defined DEBUG_TPM_SR
+    fprintf(stderr,"tpm: CALL TO TPM_RESET!\n");
+#endif
+
+    if (thread_running) {
+#if defined DEBUG_TPM || defined DEBUG_TPM_SR
+        fprintf(stderr,"tpm: TERMINATING RUNNING TPM THREAD\n");
+#endif
+        terminate_tpm_thread();
+    }
+
+    had_fatal_error = false;
+    thread_terminate = false;
+    had_startup_error = false;
+
+    qemu_thread_create(&thread, mainLoop, &tpm_thread_params);
+    thread_running = true;
+}
+
+
+/*
+ * restore TPM volatile state from given data
+ *
+ * The data are ignore by this driver, instead we read the volatile state
+ * from the TPM block store.
+ *
+ * This function gets called by Qemu when
+ * (1) resuming after a suspend
+ * (2) resuming a snapshot
+ *
+ * (1) works fine since we get call to the reset function as well
+ * (2) requires us to call the reset function ourselves; we do this
+ *     indirectly by calling the tis_reset_for_snapshot_resume();
+ *     a sure indicator of whether this function is called due to a resume
+ *     of a snapshot is that the tpm_initialized variable is 'true'.
+ *
+ */
+static int instantiate_with_volatile_data(TPMState *s)
+{
+    if (tpm_initialized) {
+#ifdef DEBUG_TPM_SR
+        fprintf(stderr,"tpm: This is resume of a SNAPSHOT?!\n");
+#endif
+        // !!! Xen does not support this ...
+        tis_reset_for_snapshot_resume(s);
+    }
+
+    return 0;
+}
+
+
+static int init(TPMState *s, TPMRecvDataCB *recv_data_cb)
+{
+    tpm_thread_params.tpm_state = s;
+    tpm_thread_params.recv_data_callback = recv_data_cb;
+
+    qemu_mutex_init(&state_mutex);
+
+    // !!! Do necessary initialization here
+
+    atexit(tpm_atexit);
+
+    return 0;
+}
+
+
+static bool get_tpm_established_flag(void)
+{
+    return false;
+}
+
+
+static bool get_startup_error(void)
+{
+    return had_startup_error;
+}
+
+
+/**
+ * This function is called by tpm_tis.c once the TPM has processed
+ * the last command and returned the response to the TIS.
+ */
+static int save_volatile_data(void)
+{
+    if (!tpm_initialized) {
+        /* TPM was never initialized
+           volatile_state.buffer may be NULL if TPM was never used.
+         */
+        return 0;
+    }
+
+    return 0;
+}
+
+
+static size_t realloc_buffer(TPMSizedBuffer *sb)
+{
+    size_t wanted_size = 4096;
+
+    if (sb->size != wanted_size) {
+        sb->buffer = qemu_realloc(&sb->buffer, wanted_size);
+        if (sb->buffer != NULL)
+            sb->size = wanted_size;
+        else
+            sb->size = 0;
+    }
+    return sb->size;
+}
+
+
+static const char *create_desc(void)
+{
+    static int done;
+
+    if (!done) {
+        snprintf(dev_description, sizeof(dev_description),
+                 "Skeleton TPM backend");
+        done = 1;
+    }
+
+    return dev_description;
+}
+
+
+static bool handle_options(QemuOpts *opts)
+{
+    const char *value;
+
+    value = qemu_opt_get(opts, "path");
+    if (value) {
+        // !!! handle path parameter
+    } else {
+        fprintf(stderr,"-tpm is missing path= parameter\n");
+        return false;
+    }
+    return true;
+}
+
+
+struct backend_tpm_driver skeleton = {
+    .id                             = "skeleton",
+    .desc                           = create_desc,
+    .handle_options                 = handle_options,
+    .init                           = init,
+    .late_startup_tpm               = late_startup_tpm,
+    .realloc_buffer                 = realloc_buffer,
+    .reset                          = reset,
+    .had_startup_error              = get_startup_error,
+    .save_volatile_data             = save_volatile_data,
+    .load_volatile_data             = instantiate_with_volatile_data,
+    .get_tpm_established_flag       = get_tpm_established_flag,
+};