[PATCH] efi: payload: inform users on attempt to boot non EFI-stubbed kernel

[Michael Taubert]

Tested-by: Michael Taubert <info at arachnodroid.de>

Am 20.06.24 um 09:16 schrieb Ahmad Fatoum:
> Calling bootm on an x86 kernel image that lacks an EFI stub will result
> in a "no image handler found for image type MBR sector", which can be
> very confusing.
>
> Improve upon this by directly suggesting that the kernel's
> CONFIG_EFI_STUB option needs to be enabled, so the image has the
> expected PE magic (and the EFI stub code that comes with it).
>
> Cc: cybin <info at arachnodroid.de>
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
>   efi/payload/image.c | 23 +++++++++++++++++++++++
>   1 file changed, 23 insertions(+)
>
> diff --git a/efi/payload/image.c b/efi/payload/image.c
> index 0795010cd9d2..6a41338f2a2f 100644
> --- a/efi/payload/image.c
> +++ b/efi/payload/image.c
> @@ -337,6 +337,26 @@ static struct binfmt_hook binfmt_efi_hook = {
>   	.hook = efi_execute,
>   };
>   
> +static int do_bootm_mbr(struct image_data *data)
> +{
> +	/* On x86, Linux kernel images have a MBR magic at the end of
> +	 * the first 512 byte sector and a PE magic if they're EFI-stubbed.
> +	 * The PE magic has precedence over the MBR, so if we arrive in
> +	 * this boot handler, the kernel has no EFI stub.
> +	 *
> +	 * Print a descriptive error message instead of "no image handler
> +	 * found for image type MBR sector".
> +	 */
> +	pr_err("Can't boot MBR sector: Is CONFIG_EFI_STUB disabled in your Linux kernel config?\n");
> +	return -ENOSYS;
> +}
> +
> +static struct image_handler non_efi_handle_linux_x86 = {
> +	.name = "non-EFI x86 Linux Image",
> +	.bootm = do_bootm_mbr,
> +	.filetype = filetype_mbr,
> +};
> +
>   static struct binfmt_hook binfmt_arm64_efi_hook = {
>   	.type = filetype_arm64_efi_linux_image,
>   	.hook = efi_execute,
> @@ -350,6 +370,9 @@ static int efi_register_image_handler(void)
>   	if (IS_ENABLED(CONFIG_CPU_V8))
>   		binfmt_register(&binfmt_arm64_efi_hook);
>   
> +	if (IS_ENABLED(CONFIG_X86))
> +		register_image_handler(&non_efi_handle_linux_x86);
> +
>   	return 0;
>   }
>   late_efi_initcall(efi_register_image_handler);