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: <20250312185739.426a8229@pumpkin>
Date: Wed, 12 Mar 2025 18:57:39 +0000
From: David Laight <david.laight.linux@...il.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: "H. Peter Anvin" <hpa@...or.com>, 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 18:44:09 +0100
Ard Biesheuvel <ardb@...nel.org> wrote:

> On Tue, 11 Mar 2025 at 18:29, H. Peter Anvin <hpa@...or.com> wrote:
> >
> > 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.  
> 
> I.e., someone can always stick a CRC-32 into the last 4 bytes if they
> wanted to? Yeah that makes sense.

I think you'd need a comment saying the last 4 bytes are reserved in case
anyone wants to add a hash.

	David

>