[PATCH v2 7/8] efi: implement LoadFile2 initrd loading protocol for Linux

[Ard Biesheuvel]

Recent Linux kernels will invoke the LoadFile2 protocol installed on a
well-known vendor media devicepath to load the initrd if it is exposed
by the firmware. Using this method is preferred for two reasons:
- the Linux kernel is in charge of allocating the memory, and so it can
  implement any placement policy it wants (given that these tend to
  change between kernel versions),
- it is no longer necessary to modify the device tree provided by the
  firmware.

So let's install this protocol when handling the 'initrd' command if
such a recent kernel was detected (based on the PE/COFF image version),
and defer loading the initrd contents until the point where the kernel
invokes the LoadFile2 protocol.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
---
 grub-core/loader/arm64/linux.c | 109 +++++++++++++++++++-
 1 file changed, 108 insertions(+), 1 deletion(-)

diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index 28ff8584a3b5..c6a95e1f0c43 100644
--- a/grub-core/loader/arm64/linux.c
+++ b/grub-core/loader/arm64/linux.c
@@ -48,6 +48,10 @@ static grub_uint32_t cmdline_size;
 static grub_addr_t initrd_start;
 static grub_addr_t initrd_end;
 
+static struct grub_linux_initrd_context initrd_ctx = { 0, 0, 0 };
+static grub_efi_handle_t initrd_lf2_handle;
+static int initrd_use_loadfile2;
+
 grub_err_t
 grub_arch_efi_linux_load_image_header (grub_file_t file,
                                       struct linux_arch_kernel_header * lh)
@@ -81,6 +85,18 @@ grub_arch_efi_linux_load_image_header (grub_file_t file,
        return grub_error(GRUB_ERR_FILE_READ_ERROR, "failed to read COFF image 
header");
     }
 
+  /*
+   * Linux kernels built for any architecture are guaranteed to support the
+   * LoadFile2 based initrd loading protocol if the image version is >= 1.
+   */
+  if (lh->coff_image_header.optional_header.major_image_version >= 1)
+    initrd_use_loadfile2 = 1;
+  else
+    initrd_use_loadfile2 = 0;
+
+  grub_dprintf ("linux", "LoadFile2 initrd loading %sabled\n",
+               initrd_use_loadfile2 ? "en" : "dis");
+
   return GRUB_ERR_NONE;
 }
 
@@ -250,13 +266,86 @@ allocate_initrd_mem (int initrd_pages)
                                       GRUB_EFI_LOADER_DATA);
 }
 
+struct initrd_media_device_path {
+  grub_efi_vendor_media_device_path_t  vendor;
+  grub_efi_device_path_t               end;
+} GRUB_PACKED;
+
+#define LINUX_EFI_INITRD_MEDIA_GUID  \
+  { 0x5568e427, 0x68fc, 0x4f3d, \
+    { 0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68 } \
+  }
+
+static struct initrd_media_device_path initrd_lf2_device_path = {
+  {
+    {
+      GRUB_EFI_MEDIA_DEVICE_PATH_TYPE,
+      GRUB_EFI_VENDOR_MEDIA_DEVICE_PATH_SUBTYPE,
+      sizeof(grub_efi_vendor_media_device_path_t),
+    },
+    LINUX_EFI_INITRD_MEDIA_GUID
+  }, {
+    GRUB_EFI_END_DEVICE_PATH_TYPE,
+    GRUB_EFI_END_ENTIRE_DEVICE_PATH_SUBTYPE,
+    sizeof(grub_efi_device_path_t)
+  }
+};
+
+static grub_efi_status_t initrd_load_file2(grub_efi_load_file2_t *this,
+                                          grub_efi_device_path_t *device_path,
+                                          grub_efi_boolean_t boot_policy,
+                                          grub_efi_uintn_t *buffer_size,
+                                          void *buffer);
+
+static grub_efi_load_file2_t initrd_lf2 = {
+  initrd_load_file2
+};
+
+static grub_efi_status_t initrd_load_file2(grub_efi_load_file2_t *this,
+                                          grub_efi_device_path_t *device_path,
+                                          grub_efi_boolean_t boot_policy,
+                                          grub_efi_uintn_t *buffer_size,
+                                          void *buffer)
+{
+  grub_efi_status_t status = GRUB_EFI_SUCCESS;
+  grub_efi_uintn_t initrd_size;
+
+  if (!this || this != &initrd_lf2 || !buffer_size)
+    return GRUB_EFI_INVALID_PARAMETER;
+
+  if (device_path->type != GRUB_EFI_END_DEVICE_PATH_TYPE ||
+      device_path->subtype != GRUB_EFI_END_ENTIRE_DEVICE_PATH_SUBTYPE)
+    return GRUB_EFI_NOT_FOUND;
+
+  if (boot_policy)
+    return GRUB_EFI_UNSUPPORTED;
+
+  initrd_size = grub_get_initrd_size (&initrd_ctx);
+  if (!buffer || *buffer_size < initrd_size)
+    {
+      *buffer_size = initrd_size;
+      return GRUB_EFI_BUFFER_TOO_SMALL;
+    }
+
+  grub_dprintf ("linux", "Loading initrd via LOAD_FILE2_PROTOCOL\n");
+
+  if (grub_initrd_load (&initrd_ctx, NULL, buffer))
+    status = GRUB_EFI_LOAD_ERROR;
+
+  grub_initrd_close (&initrd_ctx);
+  return status;
+}
+
 static grub_err_t
 grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)),
                 int argc, char *argv[])
 {
-  struct grub_linux_initrd_context initrd_ctx = { 0, 0, 0 };
   int initrd_size, initrd_pages;
   void *initrd_mem = NULL;
+  grub_efi_guid_t load_file2_guid = GRUB_EFI_LOAD_FILE2_PROTOCOL_GUID;
+  grub_efi_guid_t device_path_guid = GRUB_EFI_DEVICE_PATH_GUID;
+  grub_efi_boot_services_t *b;
+  grub_efi_status_t status;
 
   if (argc == 0)
     {
@@ -274,6 +363,24 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ 
((unused)),
   if (grub_initrd_init (argc, argv, &initrd_ctx))
     goto fail;
 
+  if (initrd_use_loadfile2)
+    {
+      b = grub_efi_system_table->boot_services;
+      status = b->install_multiple_protocol_interfaces (&initrd_lf2_handle,
+                                                       &load_file2_guid,
+                                                       &initrd_lf2,
+                                                       &device_path_guid,
+                                                       &initrd_lf2_device_path,
+                                                       NULL);
+      if (status == GRUB_EFI_OUT_OF_RESOURCES)
+       {
+         grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+         return grub_errno;
+       }
+      grub_dprintf ("linux", "LoadFile2 initrd loading protocol installed\n");
+      return GRUB_ERR_NONE;
+    }
+
   initrd_size = grub_get_initrd_size (&initrd_ctx);
   grub_dprintf ("linux", "Loading initrd\n");
 
-- 
2.17.1