linux-kernel - Re: [tip:efi/urgent] efi: Align 'efi_guid

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Date:   Mon, 17 Dec 2018 23:33:47 +0100
From:   Heinrich Schuchardt <xypron.glpk@....de>
To:     cai@....us, torvalds@...ux-foundation.org, mingo@...nel.org,
        bp@...en8.de, dave.hansen@...ux.intel.com,
        ard.biesheuvel@...aro.org, linux-kernel@...r.kernel.org,
        luto@...nel.org, tglx@...utronix.de, riel@...riel.com,
        hpa@...or.com, peterz@...radead.org,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:efi/urgent] efi: Align 'efi_guid_t' to 64 bits

On 12/17/18 7:16 PM, tip-bot for Heinrich Schuchardt wrote:
> Commit-ID:  793423cf07e51e3185b8680167115813589c057d
> Gitweb:     https://git.kernel.org/tip/793423cf07e51e3185b8680167115813589c057d
> Author:     Heinrich Schuchardt <xypron.glpk@....de>
> AuthorDate: Mon, 17 Dec 2018 19:02:14 +0100
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Mon, 17 Dec 2018 19:12:48 +0100
> 
> efi: Align 'efi_guid_t' to 64 bits
> 
> The UEFI Specification Version 2.7 Errata A defines:
> 
>   "EFI_GUID
>   128-bit buffer containing a unique identifier value.
>   Unless otherwise specified, aligned on a 64-bit boundary."
> 
> Before this patch efi_guid_t was only 8-bit aligned.
> 
> Note that this could potentially trigger alignment faults during
> EFI runtime services calls on 32-bit ARM, given that it does not
> permit load/store double or load/store multiple instructions to
> operate on memory addresses that are not 32-bit aligned.
> 
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@....de>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: <stable@...r.kernel.org> # v4.9+, or earlier if possible
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Qian Cai <cai@....us>
> Cc: Rik van Riel <riel@...riel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: linux-efi@...r.kernel.org
> Link: http://lkml.kernel.org/r/20181217180214.9436-3-ard.biesheuvel@linaro.org
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
>  include/linux/efi.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 100ce4a4aff6..e6480c805932 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -48,7 +48,7 @@ typedef u16 efi_char16_t;		/* UNICODE character */
>  typedef u64 efi_physical_addr_t;
>  typedef void *efi_handle_t;
>  
> -typedef guid_t efi_guid_t;
> +	
>  
>  #define EFI_GUID(a,b,c,d0,d1,d2,d3,d4,d5,d6,d7) \
>  	GUID_INIT(a, b, c, d0, d1, d2, d3, d4, d5, d6, d7)
> 

Before rushing this patch in, we should carefully review its side
effects, e.g. on 32bit system this changes the size of
efi_config_table_32_t from 20 to 24, which is part of the interface to
the UEFI firmware.

Best regards

Heinrich