[PATCH resend 8/9] efi: implement LoadFile2 initrd loading protocol for Linux

Ard Biesheuvel
2022-08-18T08:56:13Z

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>
---
grub-core/loader/arm64/linux.c | 129 +++++++++++++++++++-
1 file changed, 128 insertions(+), 1 deletion(-)

diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
index 56ba8d0a6ea3..82c7558b4c4c 100644
--- a/grub-core/loader/arm64/linux.c
+++ b/grub-core/loader/arm64/linux.c
@@ -48,6 +48,48 @@ static grub_uint32_t cmdline_size;
static grub_addr_t initrd_start;
static grub_addr_t initrd_end;

+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 struct grub_linux_initrd_context initrd_ctx = { 0, 0, 0 };
+static grub_efi_handle_t initrd_lf2_handle;
+static int initrd_use_loadfile2;
+
+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
+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 +120,18 @@ 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;
}

@@ -197,6 +251,8 @@ grub_linux_boot (void)
static grub_err_t
grub_linux_unload (void)
{
+ grub_efi_boot_services_t *b;
+
grub_dl_unref (my_mod);
loaded = 0;
if (initrd_start)
@@ -208,6 +264,19 @@ 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)
+ {
+ b = grub_efi_system_table->boot_services;
+ 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 = 0;
+ }
return GRUB_ERR_NONE;
}

@@ -247,13 +316,50 @@ allocate_initrd_mem (int initrd_pages)
GRUB_EFI_LOADER_DATA);
}

+static grub_efi_status_t
+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 || 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", "Providing initrd via LOAD_FILE2_PROTOCOL\n");
+
+ if (grub_initrd_load (&initrd_ctx, 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_boot_services_t *b;
+ grub_efi_status_t status;

if (argc == 0)
{
@@ -271,6 +377,27 @@ 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)
+ {
+ 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", "Using LoadFile2 initrd loading protocol\n");
+ return GRUB_ERR_NONE;
+ }
+
initrd_size = grub_get_initrd_size (&initrd_ctx);
grub_dprintf ("linux", "Loading initrd\n");

--
2.35.1