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: <CAMj1kXHZsk68kVA=dFbCb3yCrLJmHvn7HZ-qqSjjuQkdUf9_2Q@mail.gmail.com>
Date: Tue, 11 Mar 2025 18:25:15 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: "H. Peter Anvin" <hpa@...or.com>
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 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?