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Message-ID: <20170207183056.42gqqg2jp32jexmy@redhat.com>
Date: Tue, 7 Feb 2017 13:30:57 -0500
From: Peter Jones <pjones@...hat.com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org, will.deacon@....com,
catalin.marinas@....com, mark.rutland@....com,
labbott@...oraproject.org, kernel-hardening@...ts.openwall.com,
leif.lindholm@...aro.org
Subject: Re: [PATCH 5/7] arm64: efi: remove pointless dummy .reloc section
On Mon, Feb 06, 2017 at 04:24:33PM +0000, Ard Biesheuvel wrote:
> The kernel's EFI PE/COFF header contains a dummy .reloc section, and
> an explanatory comment that claims that this is required for the EFI
> application loader to accept the Image as a relocatable image (i.e.,
> one that can be loaded at any offset and fixed up in place)
>
> This was inherited from the x86 implementation, which has elaborate host
> tooling to mangle the PE/COFF header post-link time, and which populates
> the .reloc section with a single dummy base relocation. On ARM, no such
> tooling exists, and the .reloc section remains empty, and is never even
> exposed via the BaseRelocationTable directory entry, which is where the
> PE/COFF loader looks for it.
>
> The PE/COFF spec is unclear about relocatable images that do not require
> any fixups, but the EDK2 implementation, which is the de facto reference
> for PE/COFF in the UEFI space, clearly does not care, and explicitly
> mentions (in a comment) that relocatable images with no base relocations
> are perfectly fine, as long as they don't have the RELOCS_STRIPPED
> attribute set (which is not the case for our PE/COFF image)
>
> So simply remove the .reloc section altogether.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Looks completely reasonable to me.
Acked-by: Peter Jones <pjones@...hat.com>
> ---
> arch/arm64/kernel/efi-header.S | 22 +-------------------
> 1 file changed, 1 insertion(+), 21 deletions(-)
>
> diff --git a/arch/arm64/kernel/efi-header.S b/arch/arm64/kernel/efi-header.S
> index 74a25c09a1b8..35b11654ecc5 100644
> --- a/arch/arm64/kernel/efi-header.S
> +++ b/arch/arm64/kernel/efi-header.S
> @@ -37,7 +37,7 @@ pe_header:
> .short 0
> coff_header:
> .short 0xaa64 // AArch64
> - .short 2 // nr_sections
> + .short 1 // nr_sections
> .long 0 // TimeDateStamp
> .long 0 // PointerToSymbolTable
> .long 1 // NumberOfSymbols
> @@ -96,26 +96,6 @@ extra_header_fields:
>
> // Section table
> section_table:
> -
> - /*
> - * The EFI application loader requires a relocation section
> - * because EFI applications must be relocatable. This is a
> - * dummy section as far as we are concerned.
> - */
> - .ascii ".reloc"
> - .byte 0
> - .byte 0 // end of 0 padding of section name
> - .long 0
> - .long 0
> - .long 0 // SizeOfRawData
> - .long 0 // PointerToRawData
> - .long 0 // PointerToRelocations
> - .long 0 // PointerToLineNumbers
> - .short 0 // NumberOfRelocations
> - .short 0 // NumberOfLineNumbers
> - .long 0x42100040 // Characteristics (section flags)
> -
> -
> .ascii ".text"
> .byte 0
> .byte 0
> --
> 2.7.4
>
--
Peter
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