[PATCH v4 7/8] Add a module for the Boot Loader Interface

[Oliver Steffen]

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>
---
 docs/grub.texi              |  22 +++++
 grub-core/Makefile.core.def |   6 ++
 grub-core/commands/bli.c    | 166 ++++++++++++++++++++++++++++++++++++
 include/grub/efi/api.h      |   5 ++
 4 files changed, 199 insertions(+)
 create mode 100644 grub-core/commands/bli.c

diff --git a/docs/grub.texi b/docs/grub.texi
index 659885388..e63cad8d9 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4291,6 +4291,7 @@ you forget a command, you can run the command 
@command{help}
 * background_image::            Load background image for active terminal
 * badram::                      Filter out bad regions of RAM
 * blocklist::                   Print a block list
+* bli::                         Set Boot Loader Interface EFI variables
 * boot::                        Start up your operating system
 * cat::                         Show the contents of a file
 * clear::                       Clear the screen
@@ -4471,6 +4472,27 @@ Print a block list (@pxref{Block list syntax}) for 
@var{file}.
 @end deffn
 
 
+@node bli
+@subsection bli
+
+@deffn Command bli
+Initialize the @url{https://systemd.io/BOOT_LOADER_INTERFACE/, Boot Loader 
Interface}.
+
+This command sets two EFI variables under the vendor GUID
+@code{4a67b082-0a4c-41cf-b6c7-440b29bb8c4f}:
+
+@code{LoaderDevicePartUUID} is set to the Partition UUID of the EFI System 
Partition used during boot.
+This is needed for automatic partition discovery as described by the 
+@url{https://uapi-group.org/specifications/specs/discoverable_partitions_specification/,
+Discoverable Partitions Specification}.
+
+@code{LoaderInfo} is set to the string @code{Grub} followed by the version 
number.  This is used by
+user-space tools to identify the boot loader that was used.
+
+This command is only available on UEFI platforms.
+@end deffn
+
+
 @node boot
 @subsection boot
 
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..3ce0161a8
--- /dev/null
+++ b/grub-core/commands/bli.c
@@ -0,0 +1,166 @@
+/*
+ *  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 (const char *device_name, char **part_uuid)
+{
+  grub_device_t device;
+  grub_err_t status = GRUB_ERR_NONE;
+  grub_disk_t disk = NULL;
+  struct grub_gpt_partentry entry;
+
+  device = grub_device_open (device_name);
+  if (device == NULL)
+    {
+      status = grub_error (grub_errno, N_("error opening device: %s"), 
device_name);
+      goto fail;
+    }
+
+  disk = grub_disk_open (device->disk->name);
+  if (disk == NULL)
+    {
+      status = grub_error (grub_errno, N_("error opening disk: %s"), 
device_name);
+      return status;
+    }
+
+  if (grub_strcmp (device->disk->partition->partmap->name, "gpt") != 0)
+    {
+      status = grub_error (GRUB_ERR_BAD_PART_TABLE,
+                          N_("this is not a GPT partition table: %s"), 
device_name);
+      goto fail;
+    }
+
+  if (grub_disk_read (disk, device->disk->partition->offset,
+                     device->disk->partition->index, sizeof (entry), &entry) 
!= GRUB_ERR_NONE)
+    {
+      status = grub_error (grub_errno, N_("read error: %s"), device_name);
+      goto fail;
+    }
+
+  *part_uuid = grub_xasprintf ("%pG", &entry.guid);
+  if (*part_uuid == NULL)
+    status = grub_errno;
+
+ fail:
+  grub_disk_close (disk);
+  grub_device_close (device);
+
+  return status;
+}
+
+static grub_err_t
+set_efi_str_variable (const char *name, const grub_guid_t *guid,
+                      const char *value)
+{
+  grub_efi_char16_t *value_16;
+  grub_ssize_t len16;
+  grub_err_t status;
+
+  len16 = grub_utf8_to_utf16_alloc (value, &value_16, NULL);
+
+  if (len16 < 0)
+    return grub_errno;
+
+  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_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;
+  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"));
+
+  status = get_part_uuid (device_name, &part_uuid);
+
+  if (status == GRUB_ERR_NONE)
+    status = set_efi_str_variable ("LoaderDevicePartUUID", &bli_vendor_guid, 
part_uuid);
+  else
+    grub_error (status, N_("unable to determine partition UUID of boot 
device"));
+
+  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)
+{
+  cmd = grub_register_extcmd ("bli", grub_cmd_bli, 0, NULL,
+                             N_("Set EFI variables according to Boot Loader 
Interface spec."), NULL);
+}
+
+GRUB_MOD_FINI (bli)
+{
+  grub_unregister_extcmd (cmd);
+}
+
diff --git a/include/grub/efi/api.h b/include/grub/efi/api.h
index a6bd74b96..d5b4f8c8e 100644
--- a/include/grub/efi/api.h
+++ b/include/grub/efi/api.h
@@ -374,6 +374,11 @@
     { 0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68 } \
   }
 
+#define GRUB_EFI_VENDOR_BOOT_LOADER_INTERFACE_GUID \
+  { 0x4a67b082, 0x0a4c, 0x41cf, \
+    {0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f } \
+  }
+
 struct grub_efi_sal_system_table
 {
   grub_uint32_t signature;
-- 
2.39.2