tpm-emulator: protect concurrent ctrl_chr access

The control chardev is being used from the data thread to set the
locality of the next request. Altough the chr has a write mutex, we
may potentially read the reply from another thread request.

Add a mutex to protect from concurrent control commands.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NStefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>

hw/tpm/tpm_emulator.c

@@ -71,15 +71,21 @@ typedef struct TPMEmulator {
     ptm_cap caps; /* capabilities of the TPM */
     uint8_t cur_locty_number; /* last set locality */
     Error *migration_blocker;
+
+    QemuMutex mutex;
 } TPMEmulator;
 
 
-static int tpm_emulator_ctrlcmd(CharBackend *dev, unsigned long cmd, void *msg,
+static int tpm_emulator_ctrlcmd(TPMEmulator *tpm, unsigned long cmd, void *msg,
                                 size_t msg_len_in, size_t msg_len_out)
 {
+    CharBackend *dev = &tpm->ctrl_chr;
     uint32_t cmd_no = cpu_to_be32(cmd);
     ssize_t n = sizeof(uint32_t) + msg_len_in;
     uint8_t *buf = NULL;
+    int ret = -1;
+
+    qemu_mutex_lock(&tpm->mutex);
 
     buf = g_alloca(n);
     memcpy(buf, &cmd_no, sizeof(cmd_no));
@@ -87,17 +93,21 @@ static int tpm_emulator_ctrlcmd(CharBackend *dev, unsigned long cmd, void *msg,
 
     n = qemu_chr_fe_write_all(dev, buf, n);
     if (n <= 0) {
-        return -1;
+        goto end;
     }
 
     if (msg_len_out != 0) {
         n = qemu_chr_fe_read_all(dev, msg, msg_len_out);
         if (n <= 0) {
-            return -1;
+            goto end;
         }
     }
 
-    return 0;
+    ret = 0;
+
+end:
+    qemu_mutex_unlock(&tpm->mutex);
+    return ret;
 }
 
 static int tpm_emulator_unix_tx_bufs(TPMEmulator *tpm_emu,
@@ -154,7 +164,7 @@ static int tpm_emulator_set_locality(TPMEmulator *tpm_emu, uint8_t locty_number,
 
     DPRINTF("setting locality : 0x%x", locty_number);
     loc.u.req.loc = locty_number;
-    if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_SET_LOCALITY, &loc,
+    if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SET_LOCALITY, &loc,
                              sizeof(loc), sizeof(loc)) < 0) {
         error_setg(errp, "tpm-emulator: could not set locality : %s",
                    strerror(errno));
@@ -202,8 +212,8 @@ error:
 static int tpm_emulator_probe_caps(TPMEmulator *tpm_emu)
 {
     DPRINTF("%s", __func__);
-    if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_GET_CAPABILITY,
-                         &tpm_emu->caps, 0, sizeof(tpm_emu->caps)) < 0) {
+    if (tpm_emulator_ctrlcmd(tpm_emu, CMD_GET_CAPABILITY,
+                             &tpm_emu->caps, 0, sizeof(tpm_emu->caps)) < 0) {
         error_report("tpm-emulator: probing failed : %s", strerror(errno));
         return -1;
     }
@@ -254,8 +264,8 @@ static int tpm_emulator_startup_tpm(TPMBackend *tb)
     ptm_res res;
 
     DPRINTF("%s", __func__);
-    if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_INIT, &init, sizeof(init),
-                         sizeof(init)) < 0) {
+    if (tpm_emulator_ctrlcmd(tpm_emu, CMD_INIT, &init, sizeof(init),
+                             sizeof(init)) < 0) {
         error_report("tpm-emulator: could not send INIT: %s",
                      strerror(errno));
         goto err_exit;
@@ -278,7 +288,7 @@ static bool tpm_emulator_get_tpm_established_flag(TPMBackend *tb)
     ptm_est est;
 
     DPRINTF("%s", __func__);
-    if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_GET_TPMESTABLISHED, &est,
+    if (tpm_emulator_ctrlcmd(tpm_emu, CMD_GET_TPMESTABLISHED, &est,
                              0, sizeof(est)) < 0) {
         error_report("tpm-emulator: Could not get the TPM established flag: %s",
                      strerror(errno));
@@ -302,7 +312,7 @@ static int tpm_emulator_reset_tpm_established_flag(TPMBackend *tb,
     }
 
     reset_est.u.req.loc = tpm_emu->cur_locty_number;
-    if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_RESET_TPMESTABLISHED,
+    if (tpm_emulator_ctrlcmd(tpm_emu, CMD_RESET_TPMESTABLISHED,
                              &reset_est, sizeof(reset_est),
                              sizeof(reset_est)) < 0) {
         error_report("tpm-emulator: Could not reset the establishment bit: %s",
@@ -330,7 +340,7 @@ static void tpm_emulator_cancel_cmd(TPMBackend *tb)
         return;
     }
 
-    if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_CANCEL_TPM_CMD, &res, 0,
+    if (tpm_emulator_ctrlcmd(tpm_emu, CMD_CANCEL_TPM_CMD, &res, 0,
                              sizeof(res)) < 0) {
         error_report("tpm-emulator: Could not cancel command: %s",
                      strerror(errno));
@@ -378,8 +388,8 @@ static int tpm_emulator_prepare_data_fd(TPMEmulator *tpm_emu)
 
     qemu_chr_fe_set_msgfds(&tpm_emu->ctrl_chr, fds + 1, 1);
 
-    if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_SET_DATAFD, &res, 0,
-                    sizeof(res)) || res != 0) {
+    if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SET_DATAFD, &res, 0,
+                             sizeof(res)) < 0 || res != 0) {
         error_report("tpm-emulator: Failed to send CMD_SET_DATAFD: %s",
                      strerror(errno));
         goto err_exit;
@@ -501,6 +511,7 @@ static void tpm_emulator_inst_init(Object *obj)
     DPRINTF("%s", __func__);
     tpm_emu->options = g_new0(TPMEmulatorOptions, 1);
     tpm_emu->cur_locty_number = ~0;
+    qemu_mutex_init(&tpm_emu->mutex);
 }
 
 /*
@@ -510,8 +521,7 @@ static void tpm_emulator_shutdown(TPMEmulator *tpm_emu)
 {
     ptm_res res;
 
-    if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_SHUTDOWN, &res, 0,
-                             sizeof(res)) < 0) {
+    if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SHUTDOWN, &res, 0, sizeof(res)) < 0) {
         error_report("tpm-emulator: Could not cleanly shutdown the TPM: %s",
                      strerror(errno));
     } else if (res != 0) {
@@ -536,6 +546,8 @@ static void tpm_emulator_inst_finalize(Object *obj)
         migrate_del_blocker(tpm_emu->migration_blocker);
         error_free(tpm_emu->migration_blocker);
     }
+
+    qemu_mutex_destroy(&tpm_emu->mutex);
 }
 
 static void tpm_emulator_class_init(ObjectClass *klass, void *data)