efi/libstub: arm64: Double check image alignment at entry - checked against EFI_KIMG_ALIGN or SEGMENT_ALIGN

efi/libstub: arm64: Double check image alignment at entry - checked against EFI_KIMG_ALIGN or SEGMENT_ALIGN

[Mihai Carabas]

Hello Ard,

In patch 'efi/libstub: arm64: Double check image alignment at entry'
(c32ac11da3f83bb42b986702a9b92f0a14ed4182) you added the following check:

if (!IS_ALIGNED((u64)_text, EFI_KIMG_ALIGN))
     efi_err("FIRMWARE BUG: kernel image not aligned on %ldk boundary\n", +
EFI_KIMG_ALIGN >> 10);

Unfortunatelly the kernel is aligned at SEGMENT_SIZE and this is the size
populated in the PE headers:

arch/arm64/kernel/efi-header.S: .long   SEGMENT_ALIGN
// SectionAlignment

EFI_KIMG_ALIGN is defined as: (SEGMENT_ALIGN > THREAD_ALIGN ? SEGMENT_ALIGN
: THREAD_ALIGN)

So it depends on THREAD_ALIGN. On newer builds these message started to
appear even though the loader (Grub) is taking into account the PE header
(which is stating 64K).

Did you want to also modify the alignment in the headers/linkers or may be
check against SEGMENT_ALIGN?

Thank you,
Mihai

Re: efi/libstub: arm64: Double check image alignment at entry - checked against EFI_KIMG_ALIGN or SEGMENT_ALIGN

[Ard Biesheuvel]

On Fri, 14 Jan 2022 at 08:29, Mihai Carabas <mihai.carabas@oracle.com> wrote:
>
> Hello Ard,
>
> In patch 'efi/libstub: arm64: Double check image alignment at entry'
> (c32ac11da3f83bb42b986702a9b92f0a14ed4182) you added the following check:
>
> if (!IS_ALIGNED((u64)_text, EFI_KIMG_ALIGN))
>      efi_err("FIRMWARE BUG: kernel image not aligned on %ldk boundary\n", +
> EFI_KIMG_ALIGN >> 10);
>
> Unfortunatelly the kernel is aligned at SEGMENT_SIZE and this is the size
> populated in the PE headers:
>
> arch/arm64/kernel/efi-header.S: .long   SEGMENT_ALIGN
> // SectionAlignment
>
> EFI_KIMG_ALIGN is defined as: (SEGMENT_ALIGN > THREAD_ALIGN ? SEGMENT_ALIGN
> : THREAD_ALIGN)
>
> So it depends on THREAD_ALIGN. On newer builds these message started to
> appear even though the loader (Grub) is taking into account the PE header
> (which is stating 64K).
>
> Did you want to also modify the alignment in the headers/linkers or may be
> check against SEGMENT_ALIGN?
>

Thanks for the report.

I missed that 64k pages kernels will need more alignment than what
they describe in the PE/COFF header. 64k is the maximum here so we
should check against SEGMENT_ALIGN not EFI_KIMG_ALIGN for the warning.