linux-kernel - Re: [RFC PATCH resend] x86/boot: Drop CRC-32 checksum and the build tool that generates it

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Message-ID: <988E1140-BF0F-49CF-AA0B-D05741148836@zytor.com>
Date: Tue, 11 Mar 2025 10:29:43 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Ard Biesheuvel <ardb@...nel.org>
CC: Vitaly Kuznetsov <vkuznets@...hat.com>,
        Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Gerd Hoffmann <kraxel@...hat.com>,
        Juergen Gross <jgross@...e.com>, Jan Beulich <jbeulich@...e.com>,
        Paul Durrant <paul@....org>, David Woodhouse <dwmw2@...radead.org>
Subject: Re: [RFC PATCH resend] x86/boot: Drop CRC-32 checksum and the build tool that generates it

On March 11, 2025 10:25:15 AM PDT, Ard Biesheuvel <ardb@...nel.org> wrote:
>On Tue, 11 Mar 2025 at 18:14, H. Peter Anvin <hpa@...or.com> wrote:
>>
>> >Ard Biesheuvel <ardb+git@...gle.com> writes:
>> >
>...
>> >> it seems quite unlikely that this checksum is being used, so let's just
>> >> drop it, along with the tool that generates it.
>> >>
>> >> Instead, use simple file concatenation and truncation to combine the two
>> >> pieces into bzImage, and replace the checks on the size of the setup
>> >> block with a couple of ASSERT()s in the linker script.
>> >>
>...
>>
>> Please leave the bytes in question as explicit zeroes if possible.
>
>Keeping the
>
>. = ALIGN(. + 4, 0x200);
>
>in arch/x86/boot/compressed/vmlinux.lds.S should be sufficient to
>guarantee that the last 4 bytes of the file are zero, so it is quite
>trivial to implement. However, I'm not quite sure what purpose that
>would serve: could you elaborate?

It means if someone *does* care it will be easier for them to adjust.