Re: [PATCH v2 6/6] efi: Use generic EFI loader for x86_64 and i386

[Ard Biesheuvel]

On Thu, 11 May 2023 at 14:06, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> Switch the x86 based EFI platform builds to the generic EFI loader,
> which exposes the initrd via the LoadFile2 protocol instead of the
> x86-specific setup header. This will launch the Linux kernel via its EFI
> stub, which performs its own initialization in the EFI boot services
> context before calling ExitBootServices() and performing the bare metal
> Linux boot.
>
> Given that only Linux kernel versions v5.8 and later support this initrd
> loading method, the existing x86 loader is retained as a fallback, which
> will also be used for Linux kernels built without the EFI stub. In this
> case, GRUB calls ExitBootServices() before entering the Linux kernel,
> and all EFI related information is provided to the kernel via struct
> boot_params in the setup header, as before.
>
> Note that this means that booting EFI stub kernels older than v5.8 is
> not supported even when not using an initrd at all.

Clarification: you /can/ boot EFI stub kernels older than v5.8 but
they will use the fallback, even though their lack of LoadFIle2
support is not strictly an impediment for booting via the EFI stub if
no initrd needs to be loaded.

> Also, the EFI
> handover protocol, which has no basis in the UEFI specification, is not
> implemented.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  grub-core/Makefile.core.def   |  5 +-
>  grub-core/loader/efi/linux.c  | 51 ++++++++++++++++++--
>  grub-core/loader/i386/linux.c |  8 +++
>  include/grub/efi/efi.h        |  2 +-
>  4 files changed, 56 insertions(+), 10 deletions(-)
>
> diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
> index 8ee2bd89c4205761..bc08955ac791241a 100644
> --- a/grub-core/Makefile.core.def
> +++ b/grub-core/Makefile.core.def
> @@ -1818,11 +1818,8 @@ module = {
>    powerpc_ieee1275 = loader/powerpc/ieee1275/linux.c;
>    sparc64_ieee1275 = loader/sparc64/ieee1275/linux.c;
>    arm_coreboot = loader/arm/linux.c;
> -  arm_efi = loader/efi/linux.c;
>    arm_uboot = loader/arm/linux.c;
> -  arm64 = loader/efi/linux.c;
> -  riscv32 = loader/efi/linux.c;
> -  riscv64 = loader/efi/linux.c;
> +  efi = loader/efi/linux.c;
>    emu = loader/emu/linux.c;
>    common = loader/linux.c;
>    common = lib/cmdline.c;
> diff --git a/grub-core/loader/efi/linux.c b/grub-core/loader/efi/linux.c
> index 15e0686549d7ecca..970a4d7a5d4d464f 100644
> --- a/grub-core/loader/efi/linux.c
> +++ b/grub-core/loader/efi/linux.c
> @@ -69,6 +69,12 @@ static initrd_media_device_path_t initrd_lf2_device_path = 
> {
>    }
>  };
>
> +extern grub_err_t
> +grub_cmd_linux_x86_legacy (grub_command_t cmd, int argc, char *argv[]);
> +
> +extern grub_err_t
> +grub_cmd_initrd_x86_legacy (grub_command_t cmd, int argc, char *argv[]);
> +
>  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,
> @@ -89,8 +95,7 @@ grub_arch_efi_linux_load_image_header (grub_file_t file,
>      return grub_error(GRUB_ERR_FILE_READ_ERROR, "failed to read Linux image 
> header");
>
>    if ((lh->code0 & 0xffff) != GRUB_PE32_MAGIC)
> -    return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
> -                      N_("plain image kernel not supported - rebuild with 
> CONFIG_(U)EFI_STUB enabled"));
> +    return GRUB_ERR_NOT_IMPLEMENTED_YET;
>
>    grub_dprintf ("linux", "UEFI stub kernel:\n");
>    grub_dprintf ("linux", "PE/COFF header @ %08x\n", lh->hdr_offset);
> @@ -117,7 +122,11 @@ grub_arch_efi_linux_load_image_header (grub_file_t file,
>    if (lh->pe_image_header.optional_header.major_image_version >= 1)
>      initrd_use_loadfile2 = true;
>    else
> +#if defined(__i386__) || defined(__x86_64__)
> +    return GRUB_ERR_NOT_IMPLEMENTED_YET;
> +#else
>      initrd_use_loadfile2 = false;
> +#endif
>
>    grub_dprintf ("linux", "LoadFile2 initrd loading %sabled\n",
>                  initrd_use_loadfile2 ? "en" : "dis");
> @@ -125,6 +134,7 @@ grub_arch_efi_linux_load_image_header (grub_file_t file,
>    return GRUB_ERR_NONE;
>  }
>
> +#if !defined(__i386__) && !defined(__x86_64__)
>  static grub_err_t
>  finalize_params_linux (void)
>  {
> @@ -169,6 +179,7 @@ failure:
>    grub_fdt_unload();
>    return grub_error(GRUB_ERR_BAD_OS, "failed to install/update FDT");
>  }
> +#endif
>
>  grub_err_t
>  grub_arch_efi_linux_boot_image (grub_addr_t addr, grub_size_t size, char 
> *args)
> @@ -231,8 +242,10 @@ grub_arch_efi_linux_boot_image (grub_addr_t addr, 
> grub_size_t size, char *args)
>  static grub_err_t
>  grub_linux_boot (void)
>  {
> +#if !defined(__i386__) && !defined(__x86_64__)
>    if (finalize_params_linux () != GRUB_ERR_NONE)
>      return grub_errno;
> +#endif
>
>    return (grub_arch_efi_linux_boot_image((grub_addr_t)kernel_addr,
>                                            kernel_size, linux_args));
> @@ -253,7 +266,9 @@ grub_linux_unload (void)
>    if (kernel_addr)
>      grub_efi_free_pages ((grub_addr_t) kernel_addr,
>                          GRUB_EFI_BYTES_TO_PAGES (kernel_size));
> +#if !defined(__i386__) && !defined(__x86_64__)
>    grub_fdt_unload ();
> +#endif
>
>    if (initrd_lf2_handle != NULL)
>      {
> @@ -269,6 +284,7 @@ grub_linux_unload (void)
>    return GRUB_ERR_NONE;
>  }
>
> +#if !defined(__i386__) && !defined(__x86_64__)
>  /*
>   * As per linux/Documentation/arm/Booting
>   * ARM initrd needs to be covered by kernel linear mapping,
> @@ -304,6 +320,7 @@ allocate_initrd_mem (int initrd_pages)
>                                        GRUB_EFI_ALLOCATE_MAX_ADDRESS,
>                                        GRUB_EFI_LOADER_DATA);
>  }
> +#endif
>
>  static grub_efi_status_t __grub_efi_api
>  grub_efi_initrd_load_file2 (grub_efi_load_file2_t *this,
> @@ -345,7 +362,7 @@ static grub_err_t
>  grub_cmd_initrd (grub_command_t cmd __attribute__ ((unused)),
>                  int argc, char *argv[])
>  {
> -  int initrd_size, initrd_pages;
> +  int __attribute__ ((unused)) 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;
> @@ -356,6 +373,11 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ 
> ((unused)),
>        goto fail;
>      }
>
> +#if defined(__i386__) || defined(__x86_64__)
> +  if (!initrd_use_loadfile2)
> +    return grub_cmd_initrd_x86_legacy (cmd, argc, argv);
> +#endif
> +
>    if (!loaded)
>      {
>        grub_error (GRUB_ERR_BAD_ARGUMENT,
> @@ -391,6 +413,7 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ 
> ((unused)),
>        return GRUB_ERR_NONE;
>      }
>
> +#if !defined(__i386__) && !defined(__x86_64__)
>    initrd_size = grub_get_initrd_size (&initrd_ctx);
>    grub_dprintf ("linux", "Loading initrd\n");
>
> @@ -410,6 +433,7 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ 
> ((unused)),
>    initrd_end = initrd_start + initrd_size;
>    grub_dprintf ("linux", "[addr=%p, size=0x%x]\n",
>                 (void *) initrd_start, initrd_size);
> +#endif
>
>   fail:
>    grub_initrd_close (&initrd_ctx);
> @@ -441,8 +465,25 @@ grub_cmd_linux (grub_command_t cmd __attribute__ 
> ((unused)),
>
>    kernel_size = grub_file_size (file);
>
> -  if (grub_arch_efi_linux_load_image_header (file, &lh) != GRUB_ERR_NONE)
> -    goto fail;
> +  switch (grub_arch_efi_linux_load_image_header (file, &lh))
> +    {
> +    case GRUB_ERR_NONE:
> +      break;
> +    case GRUB_ERR_NOT_IMPLEMENTED_YET:
> +#if defined(__i386__) || defined(__x86_64__)
> +      /*
> +       * Retry with the legacy x86 boot code - it can load EFI kernels 
> without
> +       * the stub, and supports loading initrds without the LoadFile2 
> protocol
> +       */
> +      grub_file_close (file);
> +      return grub_cmd_linux_x86_legacy (cmd, argc, argv);
> +#endif
> +      grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
> +                 N_("plain image kernel not supported - rebuild with 
> CONFIG_(U)EFI_STUB enabled"));
> +      /* fall through */
> +    default:
> +      goto fail;
> +    }
>
>    grub_loader_unset();
>
> diff --git a/grub-core/loader/i386/linux.c b/grub-core/loader/i386/linux.c
> index c2385d0a561a8fc4..997647a33326eeb8 100644
> --- a/grub-core/loader/i386/linux.c
> +++ b/grub-core/loader/i386/linux.c
> @@ -1136,6 +1136,7 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ 
> ((unused)),
>    return grub_errno;
>  }
>
> +#ifndef GRUB_MACHINE_EFI
>  static grub_command_t cmd_linux, cmd_initrd;
>
>  GRUB_MOD_INIT(linux)
> @@ -1152,3 +1153,10 @@ GRUB_MOD_FINI(linux)
>    grub_unregister_command (cmd_linux);
>    grub_unregister_command (cmd_initrd);
>  }
> +#else
> +extern grub_err_t __attribute__((alias("grub_cmd_linux")))
> +grub_cmd_linux_x86_legacy (grub_command_t cmd, int argc, char *argv[]);
> +
> +extern grub_err_t __attribute__((alias("grub_cmd_initrd")))
> +grub_cmd_initrd_x86_legacy (grub_command_t cmd, int argc, char *argv[]);
> +#endif
> diff --git a/include/grub/efi/efi.h b/include/grub/efi/efi.h
> index 444bf5b0b53e31fe..d02abca7da67f787 100644
> --- a/include/grub/efi/efi.h
> +++ b/include/grub/efi/efi.h
> @@ -113,12 +113,12 @@ extern void (*EXPORT_VAR(grub_efi_net_config)) 
> (grub_efi_handle_t hnd,
>  #if defined(__arm__) || defined(__aarch64__) || defined(__riscv)
>  void *EXPORT_FUNC(grub_efi_get_firmware_fdt)(void);
>  grub_err_t EXPORT_FUNC(grub_efi_get_ram_base)(grub_addr_t *);
> +#endif
>  #include <grub/file.h>
>  grub_err_t grub_arch_efi_linux_load_image_header(grub_file_t file,
>                                                  struct 
> linux_arch_kernel_header *lh);
>  grub_err_t grub_arch_efi_linux_boot_image(grub_addr_t addr, grub_size_t size,
>                                             char *args);
> -#endif
>
>  grub_addr_t grub_efi_modules_addr (void);
>
> --
> 2.39.2
>