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Re: [Qemu-devel] [PATCH v2 25/28] tpm-emulator: protect concurrent ctrl_


From: Stefan Berger
Subject: Re: [Qemu-devel] [PATCH v2 25/28] tpm-emulator: protect concurrent ctrl_chr access
Date: Mon, 6 Nov 2017 20:11:24 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 11/06/2017 05:11 PM, Marc-André Lureau wrote:
Hi

----- Original Message -----
On 11/06/2017 01:39 PM, Marc-André Lureau wrote:
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.
Right, so there may be concurrency with the CMD_RESET/GET_TPMESTABLISHED
commands. All the other ones shouldn't be affected. It sound like a bug
in existing code.

I think so too, I'll rebase on master for 2.11, unless you can trivially 
cherry-pick it.

I could trivially cherry-pick it. Now can I send it as a pull request ?

   Stefan


Add a mutex to protect from concurrent control commands.

Signed-off-by: Marc-André Lureau <address@hidden>
Reviewed-by: Stefan Berger <address@hidden>


thanks

---
   hw/tpm/tpm_emulator.c | 44 ++++++++++++++++++++++++++++----------------
   1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/hw/tpm/tpm_emulator.c b/hw/tpm/tpm_emulator.c
index b77c0238c7..24cb61162f 100644
--- a/hw/tpm/tpm_emulator.c
+++ b/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));
@@ -200,8 +210,8 @@ 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;
       }
@@ -252,8 +262,8 @@ 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;
@@ -276,7 +286,7 @@ 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));
@@ -300,7 +310,7 @@ 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",
@@ -329,7 +339,7 @@ static void tpm_emulator_cancel_cmd(TPMBackend *tb)
       }

       /* FIXME: make the function non-blocking, or it may block a VCPU */
-    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));
@@ -377,8 +387,8 @@ 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;
@@ -494,6 +504,7 @@ 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);
   }

   /*
@@ -503,8 +514,7 @@ 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) {
@@ -529,6 +539,8 @@ 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)






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