[PATCH v1 2/2] 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>
---
 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;
+  efi = commands/boot_loader_interface.c;
+  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 -*-*/
+
+/* boot_loader_interface.c - implementation of the boot loader interface
+ */
+
+/*
+ *  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/>.
+ */
+
+#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} };
+
+static char *
+machine_get_bootdevice (void)
+{
+  grub_efi_loaded_image_t *image;
+
+  image = grub_efi_get_loaded_image (grub_efi_image_handle);
+  if (!image)
+    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;
+    }
+
+  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"));
+      goto finish;
+    }
+
+  if (grub_disk_read (disk, dev->disk->partition->offset,
+                      dev->disk->partition->index, sizeof (entry), &entry))
+    {
+      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]);
+  if (!*part_uuid)
+    {
+      status = grub_errno;
+    }
+
+finish:
+  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_efi_char16_t *value_16;
+  grub_err_t status;
+
+  len = grub_strlen (value);
+  len16 = len * GRUB_MAX_UTF16_PER_UTF8;
+
+  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);
+  value_16[len16] = 0;
+
+  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);
+  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_info (void)
+{
+  grub_err_t status;
+  status = set_efi_str_variable (
+      "LoaderInfo", &boot_loader_interface_vendor_guid, PACKAGE_STRING);
+  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;
+    }
+
+  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:
+  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);
+}
+
+GRUB_MOD_FINI (boot_loader_interface) { grub_unregister_extcmd (cmd); }
-- 
2.39.0