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

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

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.

>
> Add a mutex to protect from concurrent control commands.
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Reviewed-by: Stefan Berger <stefanb@linux.vnet.ibm.com>


> ---
>   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)