linux-kernel - Re: [PATCH] x86, relocs: move ELF relocation handling to C

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Message-ID: <CAGXu5jLoSLu7Yp9Rc=SFp55UxeKT26=Cn+zuCb_Scnuc+gPFNQ@mail.gmail.com>
Date:	Wed, 12 Jun 2013 09:26:10 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86 maintainers <x86@...nel.org>,
	David Woodhouse <David.Woodhouse@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Matt Fleming <matt.fleming@...el.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>
Subject: Re: [PATCH] x86, relocs: move ELF relocation handling to C

On Tue, Jun 11, 2013 at 11:27 PM, Pekka Enberg <penberg@...nel.org> wrote:
> Hello Kees,
>
> On Tue, Jun 11, 2013 at 9:58 PM, Kees Cook <keescook@...omium.org> wrote:
>> Moves the relocation handling into C, after decompression. This requires
>> that the decompressed size is passed to the decompression routine as
>> well so that relocations can be found. Only kernels that need relocation
>> support will use the code.
>>
>> Based on work by Neill Clift and Michael Davidson.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>
> How does the kernel benefit from this? Are there problems with the current
> assembly code? Are you planning to improve the relocation code?

Yes, this is continuing the work needed for 64-bit relocations,
ultimately needed by KASLR. As part of the work, I was asked to move
the relocation logic from assembly into C. Doing this means that there
isn't any need for duplicating the logic in the 64-bit path (e.g.
head_64.S).

Since the other relocation work is already in the tree, I wanted to
get these last two pieces in (one was a fix for the __vvar_page --
separate patch, the other is this one, allowing 64-bit relocations to
operate while also moving the logic into C).

-Kees

--
Kees Cook
Chrome OS Security
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