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

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

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.

> > 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>
> 
> 

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)
> 
> 
>