Re: [PATCH v1 2/2] Add a module for the Boot Loader Interface

[Daniel Kiper]

On Mon, Jan 16, 2023 at 12:40:53PM +0100, Oliver Steffen wrote:
> Add a new module named boot_loader_interface, which provides a command

I would prefer something shorter than boot_loader_interface. bli?

> 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/boot_loader_interface.c | 217 +++++++++++++++++++++
>  2 files changed, 223 insertions(+)
>  create mode 100644 grub-core/commands/boot_loader_interface.c
>
> diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
> index ba967aac8..23455fb71 100644
> --- a/grub-core/Makefile.core.def
> +++ b/grub-core/Makefile.core.def
> @@ -2547,3 +2547,9 @@ module = {
>    common = commands/i386/wrmsr.c;
>    enable = x86;
>  };
> +
> +module = {
> +  name = boot_loader_interface;

s/boot_loader_interface/bli/?

> +  efi = commands/boot_loader_interface.c;

Ditto and below if needed...

> +  enable = efi;
> +};
> diff --git a/grub-core/commands/boot_loader_interface.c 
> b/grub-core/commands/boot_loader_interface.c
> new file mode 100644
> index 000000000..ccd7fa3d9
> --- /dev/null
> +++ b/grub-core/commands/boot_loader_interface.c
> @@ -0,0 +1,217 @@
> +/*-*- Mode: C; c-basic-offset: 2; indent-tabs-mode: t -*-*/

Could you move this to the end of the file? Good example you can find in
the Xen project [1].

> +/* boot_loader_interface.c - implementation of the boot loader interface
> + */

Please use correct formatting for comments [2] and move this one behind
the license below.

> +/*
> + *  GRUB  --  GRand Unified Bootloader
> + *
> + *  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/>.
> + */

Please take license from the grub-core/kern/efi/sb.c file and update
year in it. You can also merge module description with the license like
it is done in the grub-core/kern/efi/sb.c.

> +#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>
> +
> +GRUB_MOD_LICENSE ("GPLv3+");
> +
> +#define MODNAME "boot_loader_interface"
> +
> +static const grub_efi_guid_t boot_loader_interface_vendor_guid =
> +  { 0x4a67b082, 0x0a4c, 0x41cf,
> +    {0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f} };

Please define this GUID as constant in the include/grub/efi/api.h (you
will find good examples how it should be done there). I expect it can
be useful for others too.

> +static char *
> +machine_get_bootdevice (void)
> +{
> +  grub_efi_loaded_image_t *image;
> +
> +  image = grub_efi_get_loaded_image (grub_efi_image_handle);
> +  if (!image)

Please compare pointers explicitly with NULL, e.g. "if (image == NULL)",
here and below...

> +    return NULL;
> +
> +  return grub_efidisk_get_device_name (image->device_handle);
> +}
> +
> +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;
> +  grub_gpt_part_guid_t *guid;
> +
> +  if (!dev || !dev->disk || !dev->disk->partition)
> +    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("invalid device"));
> +
> +  disk = grub_disk_open (dev->disk->name);
> +  if (!disk)
> +    {
> +      status = grub_errno;
> +      grub_dprintf (MODNAME, "Error opening disk\n");
> +      return grub_errno;

s/return grub_errno/return status/?

> +    }
> +
> +  if (grub_strcmp (dev->disk->partition->partmap->name, "gpt") != 0)
> +    {
> +      status = grub_error (GRUB_ERR_BAD_PART_TABLE,
> +                           N_("This is not a GPT partition table"));

All errors in the GRUB start with lower case, i.e. s/This is/this is/.

> +      goto finish;

s/finish/fail/ and below please...

> +    }
> +
> +  if (grub_disk_read (disk, dev->disk->partition->offset,
> +                      dev->disk->partition->index, sizeof (entry), &entry))

..., , &entry) != GRUB_ERR_NONE)

> +    {
> +      status = grub_errno;
> +      grub_dprintf (MODNAME, "%s: Read error\n", dev->disk->name);
> +      goto finish;
> +    }
> +
> +  guid = &entry.guid;
> +  *part_uuid = grub_xasprintf (
> +      "%08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x",
> +      grub_le_to_cpu32 (guid->data1), grub_le_to_cpu16 (guid->data2),
> +      grub_le_to_cpu16 (guid->data3), guid->data4[0], guid->data4[1],
> +      guid->data4[2], guid->data4[3], guid->data4[4], guid->data4[5],
> +      guid->data4[6], guid->data4[7]);

I think this is generic thing and can be converted into a function.
Similar code is in the grub-core/commands/probe.c and util/grub-probe.c.
It seems to me it is at least easy to make one function for the GRUB
core code. Please do that. Of course in separate patch.

> +  if (!*part_uuid)
> +    {
> +      status = grub_errno;
> +    }

Please drop redundant braces.

> +finish:

Labels should be prefixed with a space...

> +  grub_disk_close (disk);
> +
> +  return status;
> +}
> +
> +static grub_err_t
> +set_efi_str_variable (const char *name, const grub_efi_guid_t *guid,
> +                      const char *value)
> +{
> +  grub_size_t len;
> +  grub_size_t len16;

grub_size_t len, len16;

> +  grub_efi_char16_t *value_16;
> +  grub_err_t status;
> +
> +  len = grub_strlen (value);
> +  len16 = len * GRUB_MAX_UTF16_PER_UTF8;

What will happen when len == 0?

Is there any chance for overflow here? If yes please use overflow aware
operators from include/grub/safemath.h here.

> +  value_16 = grub_calloc (len16 + 1, sizeof (value_16[0]));
> +  if (!value_16)
> +    return grub_errno;
> +
> +  len16
> +      = grub_utf8_to_utf16 (value_16, len16, (grub_uint8_t *)value, len, 
> NULL);

Please do not break lines in that way. It is difficult to read.

Here you can just do

  len16 = grub_utf8_to_utf16 (value_16, len16, (grub_uint8_t *)value, len, 
NULL);

> +  value_16[len16] = 0;
> +
> +  status = grub_efi_set_variable_with_attributes (
> +      name, guid, (void *)value_16, (len16 + 1) * sizeof (value_16[0]),

s/(void *)value_16/(void *) value_16/

Casts require a space... Please fix this kinds of problems everywhere.

> +      GRUB_EFI_VARIABLE_BOOTSERVICE_ACCESS | 
> GRUB_EFI_VARIABLE_RUNTIME_ACCESS);
> +  if (status != GRUB_ERR_NONE)

Yeah, I like this explicit comparison...

> +    {
> +      grub_dprintf (MODNAME, "Error setting EFI variable %s: %d\n", name,
> +                    status);
> +    }

Please do not add braces if they are not needed...

> +  grub_free (value_16);
> +
> +  return status;
> +}
> +
> +static grub_err_t
> +set_loader_info (void)
> +{
> +  grub_err_t status;

You do not need the status variable here. Just return immediately status from 
the
set_efi_str_variable() call.

> +  status = set_efi_str_variable (
> +      "LoaderInfo", &boot_loader_interface_vendor_guid, PACKAGE_STRING);

  return set_efi_str_variable ("LoaderInfo", 
&boot_loader_interface_vendor_guid, PACKAGE_STRING);

I am OK with lines (a bit) longer than 80 chars when it increases readability.

> +  return status;
> +}
> +
> +static grub_err_t
> +set_loader_device_part_uuid (void)
> +{
> +  grub_err_t status = GRUB_ERR_NONE;
> +  char *device_name = NULL;
> +  grub_device_t device;
> +  char *part_uuid = NULL;
> +
> +  device_name = machine_get_bootdevice ();
> +  if (!device_name)
> +    {
> +      return grub_error (GRUB_ERR_BAD_DEVICE,
> +                         N_("Unable to find boot device"));
> +    }
> +
> +  device = grub_device_open (device_name);
> +  if (!device)
> +    {
> +      status = grub_errno;
> +      grub_dprintf (MODNAME, "Error opening device: %s", device_name);
> +      goto err;

s/err/fail/ and below please...

> +    }
> +
> +  status = get_part_uuid (device, &part_uuid);
> +
> +  grub_device_close (device);
> +
> +  if (status == GRUB_ERR_NONE)
> +    {
> +      status = set_efi_str_variable ("LoaderDevicePartUUID",
> +                                     &boot_loader_interface_vendor_guid,
> +                                     part_uuid);
> +    }
> +
> +err:

Missing space before label.

> +  grub_free (part_uuid);
> +  grub_free (device_name);
> +  return status;
> +}
> +
> +static grub_err_t
> +grub_cmd_boot_loader_interface (grub_extcmd_context_t ctxt __attribute__ 
> ((unused)),
> +                                int argc __attribute__ ((unused)),
> +                                char **args __attribute__ ((unused)))
> +{
> +  grub_err_t status;
> +
> +  status = set_loader_info ();
> +  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 (boot_loader_interface)
> +{
> +  grub_dprintf (MODNAME, "%s got here\n", __func__);
> +  cmd = grub_register_extcmd (
> +      "boot_loader_interface", grub_cmd_boot_loader_interface, 0, NULL,
> +      N_("Set EFI variables according to Boot Loader Interface spec."), 
> NULL);

This kind of formatting does not parse well...

  cmd = grub_register_extcmd ("boot_loader_interface", 
grub_cmd_boot_loader_interface, 0, NULL,
                              N_("Set EFI variables according to Boot Loader 
Interface spec."), NULL);

Please fix similar problem everywhere.

> +}
> +
> +GRUB_MOD_FINI (boot_loader_interface) { grub_unregister_extcmd (cmd); }

GRUB_MOD_FINI (boot_loader_interface)
{
  grub_unregister_extcmd (cmd);
}

Daniel

[1] 
https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/spec_ctrl.c;h=e80e2a5ed1a9b61bce564f83baf95492ff17198d;hb=HEAD
[2] https://www.gnu.org/software/grub/manual/grub-dev/grub-dev.html#Comments