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

[Ard Biesheuvel]

On Tue, 11 Mar 2025 at 18:29, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>
> On March 11, 2025 10:25:15 AM PDT, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> >On Tue, 11 Mar 2025 at 18:14, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> >>
> >> >Ard Biesheuvel <ardb+git@xxxxxxxxxx> 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.