Re: [PATCH v2 4/4] ibmvtpm: Add support for trusted boot using a vTPM 2.0

[Daniel Kiper <dkiper@net-space.pl>]

On Tue, Jul 20, 2021 at 05:14:49PM -0400, Stefan Berger wrote:
> From: Stefan Berger <stefanb@linux.ibm.com>
>
> Add support for trusted boot using a vTPM 2.0 on the IBM IEEE1275
> PowerPC platform. With this patch grub now measures text and binary data
> into the TPM's PCRs 8 and 9 in the same way as the x86_64 platform
> does.
>
> Cc: Eric Snowberg <eric.snowberg@oracle.com>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
>  docs/grub.texi                        |   3 +-
>  grub-core/Makefile.core.def           |   7 ++
>  grub-core/commands/ieee1275/ibmvtpm.c | 169 ++++++++++++++++++++++++++
>  3 files changed, 178 insertions(+), 1 deletion(-)
>  create mode 100644 grub-core/commands/ieee1275/ibmvtpm.c
>
> diff --git a/docs/grub.texi b/docs/grub.texi
> index f8b4b3b21..23d2f2d90 100644
> --- a/docs/grub.texi
> +++ b/docs/grub.texi
> @@ -6023,7 +6023,8 @@ tpm module is loaded. As such it is recommended that the tpm module be built
>  into @file{core.img} in order to avoid a potential gap in measurement between
>  @file{core.img} being loaded and the tpm module being loaded.
>
> -Measured boot is currently only supported on EFI platforms.
> +Measured boot is currently only supported on EFI and IBM IEEE1275 PowerPC
> +platforms.
>
>  @node Lockdown
>  @section Lockdown when booting on a secure setup
> diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
> index 8022e1c0a..e6ac50704 100644
> --- a/grub-core/Makefile.core.def
> +++ b/grub-core/Makefile.core.def
> @@ -1118,6 +1118,13 @@ module = {
>    enable = powerpc_ieee1275;
>  };
>
> +module = {
> +  name = tpm;
> +  common = commands/tpm.c;
> +  ieee1275 = commands/ieee1275/ibmvtpm.c;
> +  enable = powerpc_ieee1275;
> +};
> +
>  module = {
>    name = terminal;
>    common = commands/terminal.c;
> diff --git a/grub-core/commands/ieee1275/ibmvtpm.c b/grub-core/commands/ieee1275/ibmvtpm.c
> new file mode 100644
> index 000000000..d61cb111a
> --- /dev/null
> +++ b/grub-core/commands/ieee1275/ibmvtpm.c
> @@ -0,0 +1,169 @@
> +/*
> + *  GRUB  --  GRand Unified Bootloader
> + *  Copyright (C) 2021  Free Software Foundation, Inc.
> + *  Copyright (C) 2021  IBM Corporation
> + *
> + *  GRUB is free software: you can redistribute it and/or modify
> + *  it under the terms of the GNU General Public License as published by
> + *  the Free Software Foundation, either version 3 of the License, or
> + *  (at your option) any later version.
> + *
> + *  GRUB 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 GRUB.  If not, see <http://www.gnu.org/licenses/>.
> + *
> + *  IBM vTPM support code.
> + */
> +
> +#include <grub/err.h>
> +#include <grub/types.h>
> +#include <grub/tpm.h>
> +#include <grub/ieee1275/ieee1275.h>
> +#include <grub/mm.h>
> +#include <grub/misc.h>
> +
> +struct tpm_2hash_ext_log
> +{
> +  struct grub_ieee1275_common_hdr common;
> +  grub_ieee1275_cell_t method;
> +  grub_ieee1275_cell_t ihandle;
> +  grub_ieee1275_cell_t size;
> +  grub_ieee1275_cell_t buf;
> +  grub_ieee1275_cell_t description_size;
> +  grub_ieee1275_cell_t description;
> +  grub_ieee1275_cell_t eventtype;
> +  grub_ieee1275_cell_t pcrindex;
> +  grub_ieee1275_cell_t catch_result;
> +  grub_ieee1275_cell_t rc;
> +};

Huh! It looks that the struct should be defined in ibmvtpm_2hash_ext_log()
as it is done in the similar GRUB IEEE1275 code. Please move it back there.
Sorry for the confusion.

> +#define IEEE1275_CELL_TRUE     ((grub_ieee1275_cell_t) -1)

This smells like global constant. Does not it? If yes could you define it
in a global header and use it? Maybe even replace existing comparisons
in the IEEE1275 code with IEEE1275_CELL_TRUE. But probably then
s/IEEE1275_CELL_TRUE/GRUB_IEEE1275_CELL_TRUE/...

> +static grub_ieee1275_ihandle_t tpm_ihandle;
> +static grub_uint8_t tpm_version;
> +
> +static grub_ieee1275_ihandle_t
> +tpm_init (void)
> +{
> +  static int init_called = 0;
> +
> +  if (!init_called)
> +    {
> +      init_called = 1;

I would move this behind grub_ieee1275_open() call.

> +      grub_ieee1275_open ("/vdevice/vtpm", &tpm_ihandle);

Why do you ignore status returned by grub_ieee1275_open()?

> +    }
> +
> +  return tpm_ihandle;
> +}
> +
> +static void
> +tpm_get_tpm_version (void)
> +{
> +  static int version_probed = 0;
> +  grub_ieee1275_phandle_t vtpm;
> +  char buffer[20];
> +  grub_ssize_t buffer_size;
> +
> +  if (!version_probed)
> +    {
> +      version_probed = 1;

I would move version_probed behind this if.

> +      if (!grub_ieee1275_finddevice ("/vdevice/vtpm", &vtpm) &&
> +	  !grub_ieee1275_get_property (vtpm, "compatible", buffer,
> +				       sizeof buffer, &buffer_size) &&

s/sizeof buffer/sizeof (buffer)/

And you can use NULL instead of buffer_size.

> +	  !grub_strcmp (buffer, "IBM,vtpm20"))
> +	{
> +	  tpm_version = 2;
> +	}

Please drop these curly brackets.

> +    }
> +}
> +
> +static grub_err_t
> +tpm_handle_find (grub_ieee1275_ihandle_t *tpm_handle)
> +{
> +  *tpm_handle = tpm_init ();
> +  if (*tpm_handle == 0)
> +      return GRUB_ERR_UNKNOWN_DEVICE;
> +
> +  tpm_get_tpm_version ();
> +
> +  return GRUB_ERR_NONE;
> +}
> +
> +static int
> +ibmvtpm_2hash_ext_log (grub_uint32_t ihandle,
> +		       grub_uint8_t pcrindex,
> +		       grub_uint32_t eventtype,
> +		       const char *description,
> +		       grub_size_t description_size,
> +		       void *buf, grub_size_t size)
> +{
> +  struct tpm_2hash_ext_log args;
> +
> +  INIT_IEEE1275_COMMON (&args.common, "call-method", 8, 2);
> +  args.method = (grub_ieee1275_cell_t) "2hash-ext-log";
> +  args.ihandle = ihandle;
> +  args.pcrindex = pcrindex;
> +  args.eventtype = eventtype;
> +  args.description = (grub_ieee1275_cell_t) description;
> +  args.description_size = description_size;
> +  args.buf = (grub_ieee1275_cell_t) buf;
> +  args.size = (grub_ieee1275_cell_t) size;
> +
> +  if (IEEE1275_CALL_ENTRY_FN (&args) == -1)
> +      return -1;

Incorrect alignment of return.

> +  /*
> +   * catch_result is set if firmware does not support 2hash-ext-log
> +   * rc is TRUE (-1) on success
> +   */
> +  if ((args.catch_result) || args.rc != IEEE1275_CELL_TRUE)
> +      return -1;

Ditto.

> +  return 0;
> +}
> +
> +static grub_err_t
> +tpm2_log_event (grub_ieee1275_ihandle_t tpm_handle, unsigned char *buf,
> +		     grub_size_t size, grub_uint8_t pcr,
> +		     const char *description)
> +{
> +  static int error_displayed;

static int error_displayed = 0;

> +  int err;
> +
> +  err = ibmvtpm_2hash_ext_log (tpm_handle,
> +			       pcr, EV_IPL,
> +			       description,
> +			       grub_strlen(description) + 1,
> +			       buf, size);
> +  if (err && error_displayed < 1)

s/error_displayed < 1/!error_displayed/

> +    {
> +      error_displayed++;
> +      grub_error (GRUB_ERR_BAD_DEVICE,

s/grub_error/return grub_error/

> +	      "2HASH-EXT-LOG failed: Firmware is likely too old.\n");
> +    }
> +
> +  return GRUB_ERR_NONE;
> +}
> +
> +grub_err_t
> +grub_tpm_measure (unsigned char *buf, grub_size_t size, grub_uint8_t pcr,
> +		  const char *description)
> +{
> +  grub_ieee1275_ihandle_t tpm_handle;
> +
> +  /* Absence of a TPM isn't a failure. */
> +  if (tpm_handle_find (&tpm_handle) != GRUB_ERR_NONE)
> +      return GRUB_ERR_NONE;

Incorrect alignment of return.

> +  grub_dprintf ("tpm", "log_event, pcr = %d, size = 0x%" PRIxGRUB_SIZE ", %s\n",
> +		pcr, size, description);
> +
> +  if (tpm_version == 2)
> +      return tpm2_log_event (tpm_handle, buf, size, pcr, description);

Ditto.

Daniel