[kernel-hardening] Re: [PATCH 4/7] arm64: efi: ensure that the PE/COFF header pointer appears at offset 0x3c

[Mark Rutland <mark.rutland@arm.com>]

On Mon, Feb 06, 2017 at 04:24:32PM +0000, Ard Biesheuvel wrote:
> Use a .org directive to ensure that the PE/COFF header pointer appears
> at offset 0x3c. Since the EFI header is now emitted using a macro, this
> helps ensure that the invocation of the macro remains at the correct
> offset.
> 
> At the same time, collapse two adjacent #ifdef CONFIG_EFI blocks into one,
> and replace .word with .long (which are equivalent, but the former is
> never used elsewhere)
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

As with patch 3, I would very much prefer that we left these bits in
head.S.

Thanks,
Mark.

> ---
>  arch/arm64/kernel/efi-header.S | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kernel/efi-header.S b/arch/arm64/kernel/efi-header.S
> index 8c8cd0a8192b..74a25c09a1b8 100644
> --- a/arch/arm64/kernel/efi-header.S
> +++ b/arch/arm64/kernel/efi-header.S
> @@ -22,14 +22,16 @@
>  	.endm
>  
>  	.macro	__EFI_HEADER
> -#ifdef CONFIG_EFI
> -	.long	pe_header - _head		// Offset to the PE header.
> +#ifndef CONFIG_EFI
> +	.long	0				// reserved
>  #else
> -	.word	0				// reserved
> -#endif
> +	/*
> +	 * PE/COFF requires the offset to the PE header
> +	 * to be stored at offset 0x3c into the file.
> +	 */
> +	.org	_head + 0x3c
> +	.long	pe_header - _head		// Offset to the PE header.
>  
> -#ifdef CONFIG_EFI
> -	.align 3
>  pe_header:
>  	.ascii	"PE"
>  	.short 	0
> -- 
> 2.7.4
>