unsigned long efi_main()

in efi/libstub/x86-stub.c [669:807]

• 76 lines of code
• 16 McCabe index (conditional complexity)

unsigned long efi_main(efi_handle_t handle,
			     efi_system_table_t *sys_table_arg,
			     struct boot_params *boot_params)
{
	unsigned long bzimage_addr = (unsigned long)startup_32;
	unsigned long buffer_start, buffer_end;
	struct setup_header *hdr = &boot_params->hdr;
	unsigned long addr, size;
	efi_status_t status;

	efi_system_table = sys_table_arg;

	/* Check if we were booted by the EFI firmware */
	if (efi_system_table->hdr.signature != EFI_SYSTEM_TABLE_SIGNATURE)
		efi_exit(handle, EFI_INVALID_PARAMETER);

	/*
	 * If the kernel isn't already loaded at a suitable address,
	 * relocate it.
	 *
	 * It must be loaded above LOAD_PHYSICAL_ADDR.
	 *
	 * The maximum address for 64-bit is 1 << 46 for 4-level paging. This
	 * is defined as the macro MAXMEM, but unfortunately that is not a
	 * compile-time constant if 5-level paging is configured, so we instead
	 * define our own macro for use here.
	 *
	 * For 32-bit, the maximum address is complicated to figure out, for
	 * now use KERNEL_IMAGE_SIZE, which will be 512MiB, the same as what
	 * KASLR uses.
	 *
	 * Also relocate it if image_offset is zero, i.e. the kernel wasn't
	 * loaded by LoadImage, but rather by a bootloader that called the
	 * handover entry. The reason we must always relocate in this case is
	 * to handle the case of systemd-boot booting a unified kernel image,
	 * which is a PE executable that contains the bzImage and an initrd as
	 * COFF sections. The initrd section is placed after the bzImage
	 * without ensuring that there are at least init_size bytes available
	 * for the bzImage, and thus the compressed kernel's startup code may
	 * overwrite the initrd unless it is moved out of the way.
	 */

	buffer_start = ALIGN(bzimage_addr - image_offset,
			     hdr->kernel_alignment);
	buffer_end = buffer_start + hdr->init_size;

	if ((buffer_start < LOAD_PHYSICAL_ADDR)				     ||
	    (IS_ENABLED(CONFIG_X86_32) && buffer_end > KERNEL_IMAGE_SIZE)    ||
	    (IS_ENABLED(CONFIG_X86_64) && buffer_end > MAXMEM_X86_64_4LEVEL) ||
	    (image_offset == 0)) {
		extern char _bss[];

		status = efi_relocate_kernel(&bzimage_addr,
					     (unsigned long)_bss - bzimage_addr,
					     hdr->init_size,
					     hdr->pref_address,
					     hdr->kernel_alignment,
					     LOAD_PHYSICAL_ADDR);
		if (status != EFI_SUCCESS) {
			efi_err("efi_relocate_kernel() failed!\n");
			goto fail;
		}
		/*
		 * Now that we've copied the kernel elsewhere, we no longer
		 * have a set up block before startup_32(), so reset image_offset
		 * to zero in case it was set earlier.
		 */
		image_offset = 0;
	}

#ifdef CONFIG_CMDLINE_BOOL
	status = efi_parse_options(CONFIG_CMDLINE);
	if (status != EFI_SUCCESS) {
		efi_err("Failed to parse options\n");
		goto fail;
	}
#endif
	if (!IS_ENABLED(CONFIG_CMDLINE_OVERRIDE)) {
		unsigned long cmdline_paddr = ((u64)hdr->cmd_line_ptr |
					       ((u64)boot_params->ext_cmd_line_ptr << 32));
		status = efi_parse_options((char *)cmdline_paddr);
		if (status != EFI_SUCCESS) {
			efi_err("Failed to parse options\n");
			goto fail;
		}
	}

	/*
	 * At this point, an initrd may already have been loaded by the
	 * bootloader and passed via bootparams. We permit an initrd loaded
	 * from the LINUX_EFI_INITRD_MEDIA_GUID device path to supersede it.
	 *
	 * If the device path is not present, any command-line initrd=
	 * arguments will be processed only if image is not NULL, which will be
	 * the case only if we were loaded via the PE entry point.
	 */
	status = efi_load_initrd(image, &addr, &size, hdr->initrd_addr_max,
				 ULONG_MAX);
	if (status != EFI_SUCCESS)
		goto fail;
	if (size > 0) {
		efi_set_u64_split(addr, &hdr->ramdisk_image,
				  &boot_params->ext_ramdisk_image);
		efi_set_u64_split(size, &hdr->ramdisk_size,
				  &boot_params->ext_ramdisk_size);
	}

	/*
	 * If the boot loader gave us a value for secure_boot then we use that,
	 * otherwise we ask the BIOS.
	 */
	if (boot_params->secure_boot == efi_secureboot_mode_unset)
		boot_params->secure_boot = efi_get_secureboot();

	/* Ask the firmware to clear memory on unclean shutdown */
	efi_enable_reset_attack_mitigation();

	efi_random_get_seed();

	efi_retrieve_tpm2_eventlog();

	setup_graphics(boot_params);

	setup_efi_pci(boot_params);

	setup_quirks(boot_params);

	status = exit_boot(boot_params, handle);
	if (status != EFI_SUCCESS) {
		efi_err("exit_boot() failed!\n");
		goto fail;
	}

	return bzimage_addr;
fail:
	efi_err("efi_main() failed!\n");

	efi_exit(handle, status);
}