Re: [PATCH] tpm: Move Linux RNG connection to hwrng

[PrasannaKumar Muralidharan]

Hi Jason,

Nice to see this patch. Some minor comments below.

On 25 October 2017 at 00:12, Jason Gunthorpe
<jgunthorpe@xxxxxxxxxxxxxxxxxxxx> wrote:
> The tpm-rng.c approach is completely inconsistent with how the kernel
> handles hotplug. Instead manage a hwrng device for each TPM. This will
> cause the kernel to read entropy from the TPM when it is plugged in,
> and allow access to the TPM rng via /dev/hwrng.
>
> Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@xxxxxxxxx>
> Signed-off-by: Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/char/hw_random/Kconfig   | 13 -----------
>  drivers/char/hw_random/Makefile  |  1 -
>  drivers/char/hw_random/tpm-rng.c | 50 ----------------------------------------
>  drivers/char/tpm/Kconfig         | 13 +++++++++++
>  drivers/char/tpm/tpm-chip.c      | 41 ++++++++++++++++++++++++++++----
>  drivers/char/tpm/tpm-interface.c | 37 ++++++++++++++++-------------
>  drivers/char/tpm/tpm.h           |  5 ++++
>  7 files changed, 76 insertions(+), 84 deletions(-)
>  delete mode 100644 drivers/char/hw_random/tpm-rng.c
>
> All,
>
> It is such a good idea, I took PrasannaKumar's patch, reviewed and
> revised it to the level it could be merged.

Thank you for this.

> This is compile tested only.
>
> diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
> index 95a031e9eced07..a20fed182cbcce 100644
> --- a/drivers/char/hw_random/Kconfig
> +++ b/drivers/char/hw_random/Kconfig
> @@ -306,19 +306,6 @@ config HW_RANDOM_POWERNV
>
>           If unsure, say Y.
>
> -config HW_RANDOM_TPM
> -       tristate "TPM HW Random Number Generator support"
> -       depends on TCG_TPM
> -       default HW_RANDOM
> -       ---help---
> -         This driver provides kernel-side support for the Random Number
> -         Generator in the Trusted Platform Module
> -
> -         To compile this driver as a module, choose M here: the
> -         module will be called tpm-rng.
> -
> -         If unsure, say Y.
> -
>  config HW_RANDOM_HISI
>         tristate "Hisilicon Random Number Generator support"
>         depends on HW_RANDOM && ARCH_HISI
> diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
> index 39a67defac67cb..91cb8e8213e7c1 100644
> --- a/drivers/char/hw_random/Makefile
> +++ b/drivers/char/hw_random/Makefile
> @@ -26,7 +26,6 @@ obj-$(CONFIG_HW_RANDOM_NOMADIK) += nomadik-rng.o
>  obj-$(CONFIG_HW_RANDOM_PSERIES) += pseries-rng.o
>  obj-$(CONFIG_HW_RANDOM_POWERNV) += powernv-rng.o
>  obj-$(CONFIG_HW_RANDOM_HISI)   += hisi-rng.o
> -obj-$(CONFIG_HW_RANDOM_TPM) += tpm-rng.o
>  obj-$(CONFIG_HW_RANDOM_BCM2835) += bcm2835-rng.o
>  obj-$(CONFIG_HW_RANDOM_IPROC_RNG200) += iproc-rng200.o
>  obj-$(CONFIG_HW_RANDOM_MSM) += msm-rng.o
> diff --git a/drivers/char/hw_random/tpm-rng.c b/drivers/char/hw_random/tpm-rng.c
> deleted file mode 100644
> index d6d448266f0752..00000000000000
> --- a/drivers/char/hw_random/tpm-rng.c
> +++ /dev/null
> @@ -1,50 +0,0 @@
> -/*
> - * Copyright (C) 2012 Kent Yoder IBM Corporation
> - *
> - * HWRNG interfaces to pull RNG data from a TPM
> - *
> - * This program is free software; you can redistribute it and/or modify
> - * it under the terms of the GNU General Public License version 2 as
> - * published by the Free Software Foundation.
> - *
> - * This program 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 General Public License for more details.
> - *
> - * You should have received a copy of the GNU General Public License
> - * along with this program; if not, write to the Free Software
> - * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
> - */
> -
> -#include <linux/module.h>
> -#include <linux/hw_random.h>
> -#include <linux/tpm.h>
> -
> -#define MODULE_NAME "tpm-rng"
> -
> -static int tpm_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> -{
> -       return tpm_get_random(TPM_ANY_NUM, data, max);
> -}
> -
> -static struct hwrng tpm_rng = {
> -       .name = MODULE_NAME,
> -       .read = tpm_rng_read,
> -};
> -
> -static int __init rng_init(void)
> -{
> -       return hwrng_register(&tpm_rng);
> -}
> -module_init(rng_init);
> -
> -static void __exit rng_exit(void)
> -{
> -       hwrng_unregister(&tpm_rng);
> -}
> -module_exit(rng_exit);
> -
> -MODULE_LICENSE("GPL v2");
> -MODULE_AUTHOR("Kent Yoder <key@xxxxxxxxxxxxxxxxxx>");
> -MODULE_DESCRIPTION("RNG driver for TPM devices");
> diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> index a30352202f1fdc..a95725fa77789e 100644
> --- a/drivers/char/tpm/Kconfig
> +++ b/drivers/char/tpm/Kconfig
> @@ -26,6 +26,19 @@ menuconfig TCG_TPM
>
>  if TCG_TPM
>
> +config HW_RANDOM_TPM
> +       tristate "TPM HW Random Number Generator support"
> +       depends on TCG_TPM && HW_RANDOM
> +       default HW_RANDOM
> +       ---help---
> +         This driver provides kernel-side support for the Random Number
> +         Generator in the Trusted Platform Module
> +
> +         To compile this driver as a module, choose M here: the
> +         module will be called tpm-rng.
> +
> +         If unsure, say Y.
> +
>  config TCG_TIS_CORE
>         tristate
>         ---help---
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index 0eca20c5a80cf2..f3571406fb2995 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -26,6 +26,7 @@
>  #include <linux/spinlock.h>
>  #include <linux/freezer.h>
>  #include <linux/major.h>
> +#include <linux/hw_random.h>
>  #include "tpm.h"
>  #include "tpm_eventlog.h"
>
> @@ -387,6 +388,26 @@ static int tpm_add_legacy_sysfs(struct tpm_chip *chip)
>
>         return 0;
>  }
> +
> +static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> +{
> +       struct tpm_chip *chip = container_of(rng, struct tpm_chip, tpm_hwrng);
> +
> +       return tpm_get_random_dev(chip, data, max);
> +}
> +
> +static int tpm_add_hwrng(struct tpm_chip *chip)
> +{
> +       if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
> +               return 0;

Can #ifndef CONFIG_HW_RANDOM_TPM be used instead? That way an if
condition can be avoided.

> +
> +       snprintf(chip->tpm_hwrng_name, sizeof(chip->tpm_hwrng_name),
> +                "tpm-rng-%d", chip->dev_num);
> +       chip->tpm_hwrng.name = chip->tpm_hwrng_name;
> +       chip->tpm_hwrng.read = tpm_hwrng_read;
> +       return hwrng_register(&chip->tpm_hwrng);
> +}
> +
>  /*
>   * tpm_chip_register() - create a character device for the TPM chip
>   * @chip: TPM chip to use.
> @@ -419,11 +440,13 @@ int tpm_chip_register(struct tpm_chip *chip)
>
>         tpm_add_ppi(chip);
>
> +       rc = tpm_add_hwrng(chip);
> +       if (rc)
> +               goto out_ppi;
> +
>         rc = tpm_add_char_device(chip);
> -       if (rc) {
> -               tpm_bios_log_teardown(chip);
> -               return rc;
> -       }
> +       if (rc)
> +               goto out_hwrng;
>
>         rc = tpm_add_legacy_sysfs(chip);
>         if (rc) {
> @@ -432,6 +455,14 @@ int tpm_chip_register(struct tpm_chip *chip)
>         }
>
>         return 0;
> +
> +out_hwrng:
> +       if (IS_ENABLED(CONFIG_HW_RANDOM_TPM))
> +               hwrng_unregister(&chip->tpm_hwrng);
> +out_ppi:
> +       tpm_bios_log_teardown(chip);
> +
> +       return rc;
>  }
>  EXPORT_SYMBOL_GPL(tpm_chip_register);
>
> @@ -451,6 +482,8 @@ EXPORT_SYMBOL_GPL(tpm_chip_register);
>  void tpm_chip_unregister(struct tpm_chip *chip)
>  {
>         tpm_del_legacy_sysfs(chip);
> +       if (IS_ENABLED(CONFIG_HW_RANDOM_TPM))
> +               hwrng_unregister(&chip->tpm_hwrng);
>         tpm_bios_log_teardown(chip);
>         if (chip->flags & TPM_CHIP_FLAG_TPM2)
>                 cdev_device_del(&chip->cdevs, &chip->devs);
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 1d6729be4cd637..310de288549818 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -1194,9 +1194,8 @@ static const struct tpm_input_header tpm_getrandom_header = {
>   *
>   * Returns < 0 on error and the number of bytes read on success
>   */
> -int tpm_get_random(u32 chip_num, u8 *out, size_t max)
> +int tpm_get_random_dev(struct tpm_chip *chip, u8 *out, size_t max)
>  {
> -       struct tpm_chip *chip;
>         struct tpm_cmd_t tpm_cmd;
>         u32 recd, num_bytes = min_t(u32, max, TPM_MAX_RNG_DATA), rlength;
>         int err, total = 0, retries = 5;
> @@ -1205,15 +1204,8 @@ int tpm_get_random(u32 chip_num, u8 *out, size_t max)
>         if (!out || !num_bytes || max > TPM_MAX_RNG_DATA)
>                 return -EINVAL;
>
> -       chip = tpm_chip_find_get(chip_num);
> -       if (chip == NULL)
> -               return -ENODEV;
> -
> -       if (chip->flags & TPM_CHIP_FLAG_TPM2) {
> -               err = tpm2_get_random(chip, out, max);
> -               tpm_put_ops(chip);
> -               return err;
> -       }
> +       if (chip->flags & TPM_CHIP_FLAG_TPM2)
> +               return tpm2_get_random(chip, out, max);
>
>         do {
>                 tpm_cmd.header.in = tpm_getrandom_header;
> @@ -1231,10 +1223,9 @@ int tpm_get_random(u32 chip_num, u8 *out, size_t max)
>
>                 rlength = be32_to_cpu(tpm_cmd.header.out.length);
>                 if (rlength < offsetof(struct tpm_getrandom_out, rng_data) +
> -                             recd) {
> -                       total = -EFAULT;
> -                       break;
> -               }
> +                             recd)
> +                       return -EFAULT;
> +
>                 memcpy(dest, tpm_cmd.params.getrandom_out.rng_data, recd);
>
>                 dest += recd;
> @@ -1242,9 +1233,23 @@ int tpm_get_random(u32 chip_num, u8 *out, size_t max)
>                 num_bytes -= recd;
>         } while (retries-- && total < max);
>
> -       tpm_put_ops(chip);
>         return total ? total : -EIO;
>  }
> +
> +int tpm_get_random(u32 chip_num, u8 *out, size_t max)
> +{
> +       int rc;
> +       struct tpm_chip *chip;
> +
> +       chip = tpm_chip_find_get(chip_num);
> +       if (chip == NULL)
> +               return -ENODEV;
> +
> +       rc = tpm_get_random_dev(chip, out, max);
> +
> +       tpm_put_ops(chip);
> +       return rc;
> +}
>  EXPORT_SYMBOL_GPL(tpm_get_random);
>
>  /**
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 2d5466a72e40f8..0e41e044d81be2 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -26,6 +26,7 @@
>  #include <linux/module.h>
>  #include <linux/delay.h>
>  #include <linux/fs.h>
> +#include <linux/hw_random.h>
>  #include <linux/mutex.h>
>  #include <linux/sched.h>
>  #include <linux/platform_device.h>
> @@ -210,6 +211,9 @@ struct tpm_chip {
>         int dev_num;            /* /dev/tpm# */
>         unsigned long is_open;  /* only one allowed */
>
> +       char tpm_hwrng_name[64];
> +       struct hwrng tpm_hwrng;
> +

Can this also be put inside the #ifdef?

>         struct mutex tpm_mutex; /* tpm is processing */
>
>         unsigned long timeout_a; /* jiffies */
> @@ -548,6 +552,7 @@ void tpm_chip_unregister(struct tpm_chip *chip);
>  void tpm_sysfs_add_device(struct tpm_chip *chip);
>
>  int tpm_pcr_read_dev(struct tpm_chip *chip, int pcr_idx, u8 *res_buf);
> +int tpm_get_random_dev(struct tpm_chip *chip, u8 *out, size_t max);
>
>  #ifdef CONFIG_ACPI
>  extern void tpm_add_ppi(struct tpm_chip *chip);
> --
> 2.7.4
>

Regards,
PrasannaKumar