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Message-ID: <20170206170640.GF4190@leverpostej> Date: Mon, 6 Feb 2017 17:06:40 +0000 From: Mark Rutland <mark.rutland@....com> To: Ard Biesheuvel <ard.biesheuvel@...aro.org> Cc: linux-arm-kernel@...ts.infradead.org, will.deacon@....com, catalin.marinas@....com, labbott@...oraproject.org, kernel-hardening@...ts.openwall.com, leif.lindholm@...aro.org, pjones@...hat.com 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> I don't have anything against this patch, so FWIW: Acked-by: Mark Rutland <mark.rutland@....com> Thanks, Mark. > --- > 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 >
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