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Date: Fri, 15 Apr 2016 11:05:15 +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:
> When INIT_SIZE is bigger than VO_INIT_SIZE (uncommon but possible),
> the copied ZO occupies the memory from extract_offset to the end of
> decompression buffer. It overlaps with the soon-to-be-uncompressed kernel
> like this:
>
> |-----compressed kernel image------|
> V V
> 0 extract_offset +INIT_SIZE
> |-----------|---------------|-------------------------|--------|
> | | | |
> VO__text startup_32 of ZO VO__end ZO__end
> ^ ^
> |-------uncompressed kernel image---------|
>
> When INIT_SIZE is equal to VO_INIT_SIZE (likely) there's still space
> left from end of ZO to the end of decompressing buffer, like below.
>
> |-compressed kernel image-|
> V V
> 0 extract_offset +INIT_SIZE
> |-----------|---------------|-------------------------|--------|
> | | | |
> VO__text startup_32 of ZO ZO__end VO__end
> ^ ^
> |------------uncompressed kernel image-------------|
>
> To simplify calculations and avoid special cases, it is cleaner to
> always place the compressed kernel image in memory so that ZO__end
> is at the end of the decompression buffer, instead of placing that
> start extract_offset as is currently done.
Btw., it would be nice to also put such a visualization (of the current layout of
these values) into the code itself.
Thanks,
Ingo
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