kernel-hardening - Re: [PATCH v5 04/21] x86, boot: Move compressed kernel to end of decompression buffer

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Date: Fri, 15 Apr 2016 10:09:56 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Yinghai Lu <yinghai@...nel.org>, Baoquan He <bhe@...hat.com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Matt Redfearn <matt.redfearn@...tec.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Vivek Goyal <vgoyal@...hat.com>,
	Andy Lutomirski <luto@...nel.org>, lasse.collin@...aani.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <dyoung@...hat.com>, kernel-hardening@...ts.openwall.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 04/21] x86, boot: Move compressed kernel to end of
 decompression buffer


* Kees Cook <keescook@...omium.org> wrote:

> From: Yinghai Lu <yinghai@...nel.org>
> 
> This change makes later calculations about where the kernel is located
> easier to reason about. To better understand this change, we must first
> clarify what VO and ZO are. They were introduced in commits by hpa:
> 
> 77d1a49 x86, boot: make symbols from the main vmlinux available
> 37ba7ab x86, boot: make kernel_alignment adjustable; new bzImage fields
> 
> Specifically:
> 
> VO:
> - uncompressed kernel image
> - size: VO__end - VO__text ("VO_INIT_SIZE" define)
> 
> ZO:
> - bootable compressed kernel image (boot/compressed/vmlinux)
> - head text + compressed kernel (VO and relocs table) + decompressor code
> - size: ZO__end - ZO_startup_32 ("ZO_INIT_SIZE" define, though see below)
> 
> The INIT_SIZE definition is used to find the larger of the two image sizes:
> 
>  #define ZO_INIT_SIZE    (ZO__end - ZO_startup_32 + ZO_z_extract_offset)
>  #define VO_INIT_SIZE    (VO__end - VO__text)
>  #if ZO_INIT_SIZE > VO_INIT_SIZE
>  #define INIT_SIZE ZO_INIT_SIZE
>  #else
>  #define INIT_SIZE VO_INIT_SIZE
>  #endif

Please also harmonize all the prefixes, i.e. use VO__/ZO__ everywhere (rename 
things where necessary), instead of this mixed up VO_/ZO_/VO__/ZO__ mess.

Thanks,

	Ingo

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