Re: [PATCH v3 06/10] Add a module for the Boot Loader Interface

[Daniel Kiper]

On Thu, Mar 02, 2023 at 07:20:41PM +0100, Oliver Steffen wrote:
> Add a new module named boot_loader_interface, which provides a command
> with the same name. It implements a small but quite useful part of the
> Boot Loader Interface [0].  This interface uses EFI variables for
> communication between the boot loader and the operating system.
>
> This module sets two EFI variables under the vendor GUID
> 4a67b082-0a4c-41cf-b6c7-440b29bb8c4f:
>
> - LoaderInfo: contains GRUB + <version number>.
>   This allows the running operating system to identify the boot loader
>   used during boot.
>
> - LoaderDevicePartUUID: contains the partition UUID of the
>   EFI System Partition (ESP).  This is used by
>   systemd-gpt-auto-generator [1] to find the root partitions (and others
>   too), via partition type IDs [2].
>
> This module is only available on EFI platforms.
>
> [0] https://systemd.io/BOOT_LOADER_INTERFACE/
> [1] 
> https://www.freedesktop.org/software/systemd/man/systemd-gpt-auto-generator.html
> [2] 
> https://uapi-group.org/specifications/specs/discoverable_partitions_specification/
>
> Signed-off-by: Oliver Steffen <osteffen@redhat.com>
> ---
>  grub-core/Makefile.core.def |   6 ++
>  grub-core/commands/bli.c    | 199 ++++++++++++++++++++++++++++++++++++
>  include/grub/efi/api.h      |   5 +
>  3 files changed, 210 insertions(+)
>  create mode 100644 grub-core/commands/bli.c
>
> diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
> index 71093a100..cdfa2d101 100644
> --- a/grub-core/Makefile.core.def
> +++ b/grub-core/Makefile.core.def
> @@ -2548,3 +2548,9 @@ module = {
>    common = commands/i386/wrmsr.c;
>    enable = x86;
>  };
> +
> +module = {
> +  name = bli;
> +  efi = commands/bli.c;
> +  enable = efi;
> +};
> diff --git a/grub-core/commands/bli.c b/grub-core/commands/bli.c
> new file mode 100644
> index 000000000..0ff44d58a
> --- /dev/null
> +++ b/grub-core/commands/bli.c
> @@ -0,0 +1,199 @@
> +/*
> + *  GRUB  --  GRand Unified Bootloader
> + *  Copyright (C) 2023  Free Software Foundation, Inc.
> + *
> + *  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/>.
> + *
> + *  Implementation of the Boot Loader Interface.
> + */
> +
> +#include <grub/charset.h>
> +#include <grub/efi/api.h>
> +#include <grub/efi/disk.h>
> +#include <grub/efi/efi.h>
> +#include <grub/err.h>
> +#include <grub/extcmd.h>
> +#include <grub/gpt_partition.h>
> +#include <grub/misc.h>
> +#include <grub/mm.h>
> +#include <grub/partition.h>
> +#include <grub/types.h>
> +
> +GRUB_MOD_LICENSE ("GPLv3+");
> +
> +#define MODNAME "bli"
> +
> +static const grub_guid_t bli_vendor_guid = 
> GRUB_EFI_VENDOR_BOOT_LOADER_INTERFACE_GUID;
> +
> +static grub_err_t
> +get_part_uuid (grub_device_t dev, char **part_uuid)
> +{
> +  grub_err_t status = GRUB_ERR_NONE;
> +  grub_disk_t disk;
> +  struct grub_gpt_partentry entry;
> +
> +  if (dev == NULL || dev->disk == NULL || dev->disk->partition == NULL)
> +    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("invalid device"));
> +
> +  disk = grub_disk_open (dev->disk->name);
> +  if (disk == NULL)
> +    {
> +      status = grub_errno;
> +      char *part = grub_partition_get_name (dev->disk->partition);

I would define "char *part = NULL;" at the beginning of the get_part_uuid()
function and move most of the grub_free() calls behind "fail" label.

> +      grub_dprintf (MODNAME, "error opening disk: %s%s%s\n", dev->disk->name,
> +                 dev->disk->partition != NULL ? "," : "",
> +                 part != NULL ? part : "UNKNOWN");
> +      grub_free (part);

Except this one...

> +      return status;
> +    }
> +
> +  if (grub_strcmp (dev->disk->partition->partmap->name, "gpt") != 0)
> +    {
> +      char *part = grub_partition_get_name (dev->disk->partition);
> +      status = grub_error (GRUB_ERR_BAD_PART_TABLE,
> +                        "this is not a GPT partition table: %s%s%s", 
> dev->disk->name,

N_("this is not a GPT partition table: %s%s%s")

> +                        dev->disk->partition != NULL ? "," : "",
> +                        part != NULL ? part : "UNKNOWN");
> +      grub_free (part);
> +      goto fail;
> +    }
> +
> +  if (grub_disk_read (disk, dev->disk->partition->offset,
> +                   dev->disk->partition->index, sizeof (entry), &entry) != 
> GRUB_ERR_NONE)
> +    {
> +      status = grub_errno;
> +      char *part = grub_partition_get_name (dev->disk->partition);
> +      grub_dprintf (MODNAME, "read error: %s%s%s\n", dev->disk->name,

Why do not you use grub_error() here? In general I think we should use
grub_error() instead of grub_dprintf() for printing errors in this function.

> +                 dev->disk->partition != NULL ? "," : "",
> +                 part != NULL ? part : "UNKNOWN");
> +      grub_free (part);
> +      goto fail;
> +    }
> +
> +  *part_uuid = grub_xasprintf ("%pG", &entry.guid);
> +  if (*part_uuid == NULL)
> +    status = grub_errno;
> +
> + fail:
> +  grub_disk_close (disk);
> +
> +  return status;
> +}
> +
> +static grub_err_t
> +set_efi_str_variable (const char *name, const grub_guid_t *guid,
> +                      const char *value)
> +{
> +  grub_size_t len, len16;
> +  grub_efi_char16_t *value_16;
> +  grub_err_t status;
> +
> +  len = grub_strlen (value);
> +
> +  /* Check for integer overflow */
> +  if (len > GRUB_SIZE_MAX / GRUB_MAX_UTF16_PER_UTF8 - 1)
> +    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("data too large"));
> +
> +  len16 = len * GRUB_MAX_UTF16_PER_UTF8;
> +
> +  value_16 = grub_calloc (len16 + 1, sizeof (value_16[0]));
> +  if (value_16 == NULL)
> +    return grub_errno;
> +
> +  len16 = grub_utf8_to_utf16 (value_16, len16, (grub_uint8_t *) value, len, 
> NULL);
> +
> +  status = grub_efi_set_variable_with_attributes (name, guid,
> +                     (void *) value_16, (len16 + 1) * sizeof (value_16[0]),
> +                     GRUB_EFI_VARIABLE_BOOTSERVICE_ACCESS
> +                     | GRUB_EFI_VARIABLE_RUNTIME_ACCESS);

                        GRUB_EFI_VARIABLE_BOOTSERVICE_ACCESS | 
GRUB_EFI_VARIABLE_RUNTIME_ACCESS);

I cannot see any reason to wrap this line.

> +  if (status != GRUB_ERR_NONE)
> +    grub_dprintf (MODNAME, "Error setting EFI variable %s: %d\n", name, 
> status);
> +
> +  grub_free (value_16);
> +
> +  return status;
> +}
> +
> +static grub_err_t
> +set_loader_device_part_uuid (void)
> +{
> +  grub_efi_loaded_image_t *image;
> +  char *device_name;
> +  grub_err_t status = GRUB_ERR_NONE;
> +  grub_device_t device;
> +  char *part_uuid = NULL;
> +
> +  image = grub_efi_get_loaded_image (grub_efi_image_handle);
> +  if (image == NULL)
> +    return grub_error (GRUB_ERR_BAD_DEVICE, N_("unable to find boot 
> device"));
> +
> +  device_name = grub_efidisk_get_device_name (image->device_handle);
> +  if (device_name == NULL)
> +    return grub_error (GRUB_ERR_BAD_DEVICE, N_("unable to find boot 
> device"));
> +
> +  device = grub_device_open (device_name);
> +  if (device == NULL)
> +    {
> +      status = grub_errno;
> +      grub_dprintf (MODNAME, "Error opening device: %s", device_name);

Again, why do not use grub_error() here?

> +      goto fail;
> +    }
> +
> +  status = get_part_uuid (device, &part_uuid);
> +
> +  grub_device_close (device);
> +
> +  if (status == GRUB_ERR_NONE)
> +    status = set_efi_str_variable ("LoaderDevicePartUUID",
> +                                &bli_vendor_guid,
> +                                part_uuid);

set_efi_str_variable ("LoaderDevicePartUUID", &bli_vendor_guid, part_uuid);

You do not need to wrap this line here.

> +
> + fail:
> +  grub_free (part_uuid);
> +  grub_free (device_name);
> +  return status;
> +}
> +
> +static grub_err_t
> +grub_cmd_bli (grub_extcmd_context_t ctxt __attribute__ ((unused)),
> +           int argc __attribute__ ((unused)),
> +           char **args __attribute__ ((unused)))
> +{
> +  grub_err_t status;
> +
> +  status = set_efi_str_variable ("LoaderInfo", &bli_vendor_guid, 
> PACKAGE_STRING);
> +  if (status != GRUB_ERR_NONE)
> +    return status;
> +
> +  status = set_loader_device_part_uuid ();
> +  if (status != GRUB_ERR_NONE)
> +    return status;
> +
> +  return GRUB_ERR_NONE;
> +}
> +
> +static grub_extcmd_t cmd;
> +
> +GRUB_MOD_INIT (bli)
> +{
> +  grub_dprintf (MODNAME, "%s got here\n", __func__);
> +  cmd = grub_register_extcmd ("bli", grub_cmd_bli, 0, NULL,
> +                           N_("Set EFI variables according to Boot Loader 
> Interface spec."), NULL);

Please add a section about this command to the docs/grub.texi. I think
it would be nice to add links to the specs there too.

Daniel