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Date: Thu, 9 Jun 2016 14:18:08 -0700
From: Kees Cook <>
To: Emese Revfy <>
Cc: "" <>, PaX Team <>, 
	Brad Spengler <>, Michal Marek <>, 
	LKML <>, 
	Masahiro Yamada <>, linux-kbuild <>, 
	"Theodore Ts'o" <>, Andrew Morton <>, Linux-MM <>, 
	Jens Axboe <>, Al Viro <>, 
	Paul McKenney <>, Ingo Molnar <>, 
	Thomas Gleixner <>,, 
	"David S. Miller" <>
Subject: Re: [PATCH v2 0/3] Introduce the latent_entropy gcc plugin

On Mon, May 30, 2016 at 4:30 PM, Emese Revfy <> wrote:
> I would like to introduce the latent_entropy gcc plugin. This plugin mitigates
> the problem of the kernel having too little entropy during and after boot
> for generating crypto keys.
> This plugin mixes random values into the latent_entropy global variable
> in functions marked by the __latent_entropy attribute.
> The value of this global variable is added to the kernel entropy pool
> to increase the entropy.
> It is a CII project supported by the Linux Foundation.
> The latent_entropy plugin was ported from grsecurity/PaX originally written by
> the PaX Team. You can find more about the plugin here:
> The plugin supports all gcc version from 4.5 to 6.0.
> I do some changes above the PaX version. The important one is mixing
> the stack pointer into the global variable too.
> You can find more about the changes here:
> This patch set is based on the "Introduce GCC plugin infrastructure" patch set (v9 next-20160520).
> Emese Revfy (3):
>  Add the latent_entropy gcc plugin
>  Mark functions with the latent_entropy attribute
>  Add the extra_latent_entropy kernel parameter
> Changes from v1:
>   * Remove unnecessary ifdefs
>     (Suggested-by: Kees Cook <>)
>   * Separate the two definitions of add_latent_entropy()
>     (Suggested-by: Kees Cook <>)
>   * Removed unnecessary global variable (latent_entropy_plugin.c)
>   * About the latent_entropy gcc attribute (latent_entropy_plugin.c)
>   * Measure the boot time performance impact of the latent_entropy plugin (arch/Kconfig)

By the way, as you work on v3, can you also be sure to put your
patches through scripts/ There are a lot of >80
character lines, and other nits. I'd like to minimize the warnings.



Kees Cook
Chrome OS & Brillo Security

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