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References: <cover.1671098103.git.baskov@ispras.ru> <cb62472011a0c4151276b6a05b83b60b1bf6f352.1671098103.git.baskov@ispras.ru>
In-Reply-To: <cb62472011a0c4151276b6a05b83b60b1bf6f352.1671098103.git.baskov@ispras.ru>
From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Fri, 10 Mar 2023 15:59:36 +0100
Message-ID: <CAMj1kXHnQZ2EDg1F_whTPHajYvqox7Ss35aqUyJuC8RLyiuCxg@mail.gmail.com>
Subject: Re: [PATCH v4 17/26] x86/boot: Reduce size of the DOS stub
To:     Evgeniy Baskov <baskov@ispras.ru>
Cc:     Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexey Khoroshilov <khoroshilov@ispras.ru>,
        Peter Jones <pjones@redhat.com>,
        "Limonciello, Mario" <mario.limonciello@amd.com>,
        joeyli <jlee@suse.com>, lvc-project@linuxtesting.org,
        x86@kernel.org, linux-efi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
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Precedence: bulk

On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@ispras.ru> wrote:
>
> This is required to fit more sections in PE section tables,
> since its size is restricted by zero page located at specific offset
> after the PE header.
>
> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> Tested-by: Peter Jones <pjones@redhat.com>
> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>

I'd prefer to rip this out altogether.

https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?id=9510f6f04f579b9a3f54ad762c75ab2d905e37d8

(and refer to the other thread in linux-efi@)

> ---
>  arch/x86/boot/header.S | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
> index 9338c68e7413..9fec80bc504b 100644
> --- a/arch/x86/boot/header.S
> +++ b/arch/x86/boot/header.S
> @@ -59,17 +59,16 @@ start2:
>         cld
>
>         movw    $bugger_off_msg, %si
> +       movw    $bugger_off_msg_size, %cx
>
>  msg_loop:
>         lodsb
> -       andb    %al, %al
> -       jz      bs_die
>         movb    $0xe, %ah
>         movw    $7, %bx
>         int     $0x10
> -       jmp     msg_loop
> +       decw    %cx
> +       jnz     msg_loop
>
> -bs_die:
>         # Allow the user to press a key, then reboot
>         xorw    %ax, %ax
>         int     $0x16
> @@ -90,10 +89,9 @@ bs_die:
>
>         .section ".bsdata", "a"
>  bugger_off_msg:
> -       .ascii  "Use a boot loader.\r\n"
> -       .ascii  "\n"
> -       .ascii  "Remove disk and press any key to reboot...\r\n"
> -       .byte   0
> +       .ascii  "Use a boot loader. "
> +       .ascii  "Press a key to reboot"
> +       .set    bugger_off_msg_size, . - bugger_off_msg
>
>  #ifdef CONFIG_EFI_STUB
>  pe_header:
> --
> 2.37.4
>