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Message-ID: <CAKv+Gu8W3fxAonQiC2mG5wxSg7X=W3PnGMi0WVEys-N6dXnY8A@mail.gmail.com>
Date: Fri, 10 Feb 2017 14:30:42 +0000
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Mark Rutland <mark.rutland@....com>
Cc: "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
Leif Lindholm <leif.lindholm@...aro.org>, Catalin Marinas <catalin.marinas@....com>,
Russell King <linux@...linux.org.uk>, kernel-hardening@...ts.openwall.com,
Laura Abbott <labbott@...oraproject.org>
Subject: Re: [PATCH v2 04/14] arm64: efi: clean up Image header after PE
header has been split off
On 10 February 2017 at 10:11, Mark Rutland <mark.rutland@....com> wrote:
> On Wed, Feb 08, 2017 at 11:55:37AM +0000, Ard Biesheuvel wrote:
>> After having split off the PE header, clean up the bits that remain:
>> use .long consistently, merge two adjacent #ifdef CONFIG_EFI blocks,
>> fix the offset of the PE header pointer and remove the redundant .align
>> that follows it.
>>
>> Also, since we will be eliminating all open coded constants from the
>> EFI header in subsequent patches, let's replace the open coded "ARM\x64"
>> magic number with its .ascii equivalent.
>>
>> No changes to the resulting binary image are intended.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> ---
>> arch/arm64/kernel/head.S | 17 ++++++++---------
>> 1 file changed, 8 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
>> index f779a7483736..aa8f6cd8c33f 100644
>> --- a/arch/arm64/kernel/head.S
>> +++ b/arch/arm64/kernel/head.S
>> @@ -91,20 +91,19 @@ _head:
>> .quad 0 // reserved
>> .quad 0 // reserved
>> .quad 0 // reserved
>> - .byte 0x41 // Magic number, "ARM\x64"
>> - .byte 0x52
>> - .byte 0x4d
>> - .byte 0x64
>> + .ascii "ARM\x64" // Magic number
>> #ifdef CONFIG_EFI
>> + /*
>> + * 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.
>
>
> Do we really need the .org? We expect all the other fields to stay in
> place without one, and it seems odd to special-case the PE header.
>
No, we don't. But the PE header offset is the only header field that
covered by a requirement that goes beyond what we stipulate ourselves,
so it makes sense to make that explicit imo. However, I'm happy to
drop it if people disagree.
> Otherwise, this looks good to me.
>
Cheers,
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