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Date: Wed, 13 Apr 2016 07:11:44 -0700
From: Kees Cook <>
To: Ingo Molnar <>
Cc: Ingo Molnar <>, LKML <>, 
	Baoquan He <>, Yinghai Lu <>, "H. Peter Anvin" <>, 
	Borislav Petkov <>, Vivek Goyal <>, Andy Lutomirski <>,, Andrew Morton <>, 
	Dave Young <>, 
	"" <>
Subject: Re: [PATCH v4 00/20] x86, boot: kaslr cleanup and 64bit kaslr support

On Wed, Apr 13, 2016 at 3:19 AM, Ingo Molnar <> wrote:
> * Kees Cook <> wrote:
>> FWIW, I've also had this tree up in my git branches, and the 0day
>> tester hasn't complained at all about it in the last two weeks. I'd
>> really like to see this in -next to fix the >4G (mainly kexec) issues
>> and get us to feature parity with the arm64 kASLR work (randomized
>> virtual address).
> So I started applying the patches, started fixing up changelogs and gave up on
> patch #3.
> Changelogs of such non-trivial code need to be proper English and need to be
> understandable.
> For example patch #3 starts with:
>> Current z_extract_offset is calculated in boot/compressed/mkpiggy.c. The problem
>> is in mkpiggy.c we don't know the detail of decompressor. Then we just get a
>> rough z_extract_offset according to extra_bytes. As we know extra_bytes can only
>> promise a safety margin when decompressing. In fact this brings some risks:
> Beyond the bad grammar of the _first word_ of the changelog, this is not a proper
> high level description of the change. A _real_ high level description would be
> something like:
>   > Currently z_extract_offset is calculated during kernel build time. The problem
>   > with that method is that at this stage we don't yet know the decompression
>   > buffer sizes - we only know that during bootup.
>   >
>   > Effects of this are that when we calculate z_extract_offset during the build
>   > we don't know the precise decompression details, we'll only get a rough
>   > estimation of z_extract_offset.
>   >
>   > Instead of that we want to calculate it during bootup.
> etc. etc. - the whole series is _full_ of such crappy changelogs that make it
> difficult for me and others to see whether the author actually _understands_ the
> existing code or is hacking away on it. It's also much harder to review and
> validate.
> This is totally unacceptable.
> Please make sure every changelog starts with a proper high level description that
> tells the story and convinces the reader about what the problem is and what the
> change should be.
> And part of that are the patch titles. Things like:
> Subject: [PATCH v3 03/19] x86, boot: Move z_extract_offset calculation to header.S
> are absolutely mindless titles. A better title would be:
>       x86/boot: Calculate precise decompressor parameters during bootup, not build time
> ... or something like that. Even having read the changelog 3 times I'm unsure what
> the change really is about.

I'll rewrite all the changelogs and resend the series. Thanks taking a look! :)


Kees Cook
Chrome OS & Brillo Security

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