linux-kernel - Re: [PATCH] efi: bump efistub version from 1.1 to 3.0 for VZLinuxBootLoader compatibility

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Message-ID: <CAMj1kXG0q-pJEnvqJxxpecVqJcB2jk3rj7S4KNp728THM=de3Q@mail.gmail.com>
Date:   Sun, 28 May 2023 20:48:26 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Akihiro Suda <suda.kyoto@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi@...r.kernel.org, Linux x86 <x86@...nel.org>
Subject: Re: [PATCH] efi: bump efistub version from 1.1 to 3.0 for
 VZLinuxBootLoader compatibility

On Sun, 28 May 2023 at 09:59, Akihiro Suda <suda.kyoto@...il.com> wrote:
>
> - LINUX_EFISTUB_MAJOR_VERSION is bumped from 1 (0b1) to 3 (0b11).
>   The value is now a bitfield.
>

OK

> The next version will be 7 (0b111).

How so? If this is going to be a monotonically increasing sequence
after all, it is still not a bit mask, and this change defeats the
purpose.

> - LINUX_EFISTUB_MINOR_VERSION is pinned to 0x0, because Apple's
>   VZLinuxBootLoader [1] cannot boot a kernel with other minor version value [2],
>   even though it does not use UEFI. Tested with macOS 13.4 (x86_64).
>
> [1] https://developer.apple.com/documentation/virtualization/vzlinuxbootloader
> [2] https://lore.kernel.org/linux-efi/CAG8fp8Teu4G9JuenQrqGndFt2Gy+V4YgJ=hN1xX7AD940YKf3A@mail.gmail.com/
>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217485
> Signed-off-by: Akihiro Suda <akihiro.suda.cz@....ntt.co.jp>

I'll queue this as a fix, but I'm going to tweak the comment (and the
commit log) a bit, if you don't mind

I'd appreciate it if you still report this as a bug with Apple, though.

Thanks,
Ard.

> ---
>  include/linux/pe.h | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/pe.h b/include/linux/pe.h
> index 5e1e11540870..ee5ade19b7eb 100644
> --- a/include/linux/pe.h
> +++ b/include/linux/pe.h
> @@ -27,9 +27,25 @@
>   * On x86, LoadImage() and StartImage() can be omitted if the EFI handover
>   * protocol is implemented, which can be inferred from the version,
>   * handover_offset and xloadflags fields in the bootparams structure.
> + *
> + * Linux EFI stub v1.1 unconditionally enabled initrd command line loader,
> + * which was previously gated by CONFIG_EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER.
> + *
> + * Linux EFI stub v3.0 changed the major version to be a bitfield (0b11).
> + * The rightmost bit means that it is compatible with v1.0 at least.
> + * The second rightmost bit means that initrd command line loader is enabled.
> + * So, there is no v2.0 (0b10), and the next version will be v7.0 (0b111).
> + */
> +#define LINUX_EFISTUB_MAJOR_VERSION            0x3
> +
> +/*
> + * LINUX_EFISTUB_MINOR_VERSION is pinned to 0x0, because Apple's
> + * VZLinuxBootLoader cannot boot a kernel with other minor version value, even
> + * though it does not use UEFI. Tested with macOS 13.4 (x86_64).
> + *
> + * https://lore.kernel.org/linux-efi/CAG8fp8Teu4G9JuenQrqGndFt2Gy+V4YgJ=hN1xX7AD940YKf3A@mail.gmail.com/
>   */
> -#define LINUX_EFISTUB_MAJOR_VERSION            0x1
> -#define LINUX_EFISTUB_MINOR_VERSION            0x1
> +#define LINUX_EFISTUB_MINOR_VERSION            0x0
>
>  /*
>   * LINUX_PE_MAGIC appears at offset 0x38 into the MS-DOS header of EFI bootable
> --
> 2.39.2