[PATCH v5 5/6] efi: implement LoadFile2 initrd loading protocol for Linux

[Ard Biesheuvel <ardb@kernel.org>]

Recent Linux kernels will invoke the LoadFile2 protocol installed on
a well-known vendor media path 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 <ardb@kernel.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---
 grub-core/commands/efi/lsefi.c |   1 +
 grub-core/loader/arm64/linux.c | 124 +++++++++++++++++++-
 include/grub/efi/api.h         |  40 +++++++
 3 files changed, 164 insertions(+), 1 deletion(-)

diff --git a/grub-core/commands/efi/lsefi.c b/grub-core/commands/efi/lsefi.c
index f46ba3b49384..c304d25ccdd6 100644
--- a/grub-core/commands/efi/lsefi.c
+++ b/grub-core/commands/efi/lsefi.c
@@ -55,6 +55,7 @@ struct known_protocol
     { GRUB_EFI_ABSOLUTE_POINTER_PROTOCOL_GUID, "absolute pointer" },
     { GRUB_EFI_DRIVER_BINDING_PROTOCOL_GUID, "EFI driver binding" },
     { GRUB_EFI_LOAD_FILE_PROTOCOL_GUID, "load file" },
+    { GRUB_EFI_LOAD_FILE2_PROTOCOL_GUID, "load file2" },
     { GRUB_EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID, "simple FS" },
     { GRUB_EFI_TAPE_IO_PROTOCOL_GUID, "tape I/O" },
     { GRUB_EFI_UNICODE_COLLATION_PROTOCOL_GUID, "unicode collation" },
diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index 754db84a96cf..9a4522d2f7bf 100644
--- a/grub-core/loader/arm64/linux.c
+++ b/grub-core/loader/arm64/linux.c
@@ -33,6 +33,7 @@
 #include <grub/i18n.h>
 #include <grub/lib/cmdline.h>
 #include <grub/verify.h>
+#include <stdbool.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
@@ -48,6 +49,39 @@ 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 = NULL;
+static bool initrd_use_loadfile2 = false;
+
+static grub_efi_guid_t load_file2_guid = GRUB_EFI_LOAD_FILE2_PROTOCOL_GUID;
+static grub_efi_guid_t device_path_guid = GRUB_EFI_DEVICE_PATH_GUID;
+
+static initrd_media_device_path_t 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 __grub_efi_api
+grub_efi_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 = {
+  grub_efi_initrd_load_file2
+};
+
 grub_err_t
 grub_arch_efi_linux_load_image_header (grub_file_t file,
                                       struct linux_arch_kernel_header * lh)
@@ -78,6 +112,18 @@ 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->pe_image_header.optional_header.major_image_version >= 1)
+    initrd_use_loadfile2 = true;
+  else
+    initrd_use_loadfile2 = false;
+
+  grub_dprintf ("linux", "LoadFile2 initrd loading %sabled\n",
+                initrd_use_loadfile2 ? "en" : "dis");
+
   return GRUB_ERR_NONE;
 }
 
@@ -197,6 +243,8 @@ grub_linux_boot (void)
 static grub_err_t
 grub_linux_unload (void)
 {
+  grub_efi_boot_services_t *b = grub_efi_system_table->boot_services;
+
   grub_dl_unref (my_mod);
   loaded = 0;
   if (initrd_start)
@@ -208,6 +256,18 @@ grub_linux_unload (void)
     grub_efi_free_pages ((grub_addr_t) kernel_addr,
 			 GRUB_EFI_BYTES_TO_PAGES (kernel_size));
   grub_fdt_unload ();
+
+  if (initrd_lf2_handle != NULL)
+    {
+      b->uninstall_multiple_protocol_interfaces (initrd_lf2_handle,
+                                                 &load_file2_guid,
+                                                 &initrd_lf2,
+                                                 &device_path_guid,
+                                                 &initrd_lf2_device_path,
+                                                 NULL);
+      initrd_lf2_handle = NULL;
+      initrd_use_loadfile2 = false;
+    }
   return GRUB_ERR_NONE;
 }
 
@@ -247,13 +307,50 @@ allocate_initrd_mem (int initrd_pages)
 				       GRUB_EFI_LOADER_DATA);
 }
 
+static grub_efi_status_t __grub_efi_api
+grub_efi_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 != &initrd_lf2 || buffer_size == NULL)
+    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 == NULL || *buffer_size < initrd_size)
+    {
+      *buffer_size = initrd_size;
+      return GRUB_EFI_BUFFER_TOO_SMALL;
+    }
+
+  grub_dprintf ("linux", "Providing initrd via EFI_LOAD_FILE2_PROTOCOL\n");
+
+  if (grub_initrd_load (&initrd_ctx, buffer))
+    status = GRUB_EFI_DEVICE_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_boot_services_t *b = grub_efi_system_table->boot_services;
+  grub_efi_status_t status;
 
   if (argc == 0)
     {
@@ -271,6 +368,31 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)),
   if (grub_initrd_init (argc, argv, &initrd_ctx))
     goto fail;
 
+  if (initrd_use_loadfile2)
+    {
+      if (initrd_lf2_handle == NULL)
+        {
+          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"));
+              goto fail;
+            }
+          else if (status != GRUB_EFI_SUCCESS)
+            {
+              grub_error (GRUB_ERR_BAD_ARGUMENT, N_("failed to install protocols"));
+              goto fail;
+            }
+        }
+      grub_dprintf ("linux", "Using LoadFile2 initrd loading protocol\n");
+      return GRUB_ERR_NONE;
+    }
+
   initrd_size = grub_get_initrd_size (&initrd_ctx);
   grub_dprintf ("linux", "Loading initrd\n");
 
diff --git a/include/grub/efi/api.h b/include/grub/efi/api.h
index b0d003aa1164..b1a7259b92c8 100644
--- a/include/grub/efi/api.h
+++ b/include/grub/efi/api.h
@@ -149,6 +149,11 @@
     { 0x8E, 0x3F, 0x00, 0xA0, 0xC9, 0x69, 0x72, 0x3B } \
   }
 
+#define GRUB_EFI_LOAD_FILE2_PROTOCOL_GUID \
+  { 0x4006c0c1, 0xfcb3, 0x403e, \
+    { 0x99, 0x6d, 0x4a, 0x6c, 0x87, 0x24, 0xe0, 0x6d } \
+  }
+
 #define GRUB_EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID \
   { 0x0964e5b22, 0x6459, 0x11d2, \
     { 0x8e, 0x39, 0x00, 0xa0, 0xc9, 0x69, 0x72, 0x3b } \
@@ -364,6 +369,11 @@
     { 0x86, 0x2e, 0xc0, 0x1c, 0xdc, 0x29, 0x1f, 0x44 } \
   }
 
+#define LINUX_EFI_INITRD_MEDIA_GUID  \
+  { 0x5568e427, 0x68fc, 0x4f3d, \
+    { 0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68 } \
+  }
+
 struct grub_efi_sal_system_table
 {
   grub_uint32_t signature;
@@ -564,6 +574,20 @@ typedef grub_uint16_t grub_efi_char16_t;
 
 typedef grub_efi_uintn_t grub_efi_status_t;
 
+/*
+ * On x86, the EFI calling convention may deviate from the local one, so
+ * callback functions exposed to the firmware must carry the follow attribute
+ * annotation. (This includes protocols implemented by GRUB that are installed
+ * into the EFI protocol database.)
+ */
+#if defined(__i386__)
+#define __grub_efi_api			__attribute__((regparm(0)))
+#elif defined(__x86_64__)
+#define __grub_efi_api			__attribute__((ms_abi))
+#else
+#define __grub_efi_api
+#endif
+
 #define GRUB_EFI_ERROR_CODE(value)	\
   ((((grub_efi_status_t) 1) << (sizeof (grub_efi_status_t) * 8 - 1)) | (value))
 
@@ -1755,6 +1779,22 @@ struct grub_efi_rng_protocol
 };
 typedef struct grub_efi_rng_protocol grub_efi_rng_protocol_t;
 
+struct grub_efi_load_file2
+{
+  grub_efi_status_t (__grub_efi_api *load_file)(struct grub_efi_load_file2 *this,
+                                                grub_efi_device_path_t *file_path,
+                                                grub_efi_boolean_t boot_policy,
+                                                grub_efi_uintn_t *buffer_size,
+                                                void *buffer);
+};
+typedef struct grub_efi_load_file2 grub_efi_load_file2_t;
+
+struct initrd_media_device_path {
+  grub_efi_vendor_media_device_path_t  vendor;
+  grub_efi_device_path_t               end;
+} GRUB_PACKED;
+typedef struct initrd_media_device_path initrd_media_device_path_t;
+
 #if (GRUB_TARGET_SIZEOF_VOID_P == 4) || defined (__ia64__) \
   || defined (__aarch64__) || defined (__MINGW64__) || defined (__CYGWIN__) \
   || defined(__riscv)
-- 
2.35.1