linux-kernel - Re: [PATCH v2 1/3] Add the latent

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Message-Id: <20160603194252.91064b8e682ad988283fc569@gmail.com>
Date:	Fri, 3 Jun 2016 19:42:52 +0200
From:	Emese Revfy <re.emese@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kernel-hardening@...ts.openwall.com, pageexec@...email.hu,
	spender@...ecurity.net, mmarek@...e.com, keescook@...omium.org,
	linux-kernel@...r.kernel.org, yamada.masahiro@...ionext.com,
	linux-kbuild@...r.kernel.org, tytso@....edu, linux-mm@...ck.org,
	axboe@...nel.dk, viro@...iv.linux.org.uk,
	paulmck@...ux.vnet.ibm.com, mingo@...hat.com, tglx@...utronix.de,
	bart.vanassche@...disk.com, davem@...emloft.net
Subject: Re: [PATCH v2 1/3] Add the latent_entropy gcc plugin

On Wed, 1 Jun 2016 12:42:27 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Tue, 31 May 2016 01:31:45 +0200 Emese Revfy <re.emese@...il.com> wrote:
> 
> > This plugin mitigates the problem of the kernel having too little entropy during
> > and after boot for generating crypto keys.
> > 
> > It creates a local variable in every marked function. The value of this variable is
> > modified by randomly chosen operations (add, xor and rol) and
> > random values (gcc generates them at compile time and the stack pointer at runtime).
> > It depends on the control flow (e.g., loops, conditions).
> > 
> > Before the function returns the plugin writes this local variable
> > into the latent_entropy global variable. The value of this global variable is
> > added to the kernel entropy pool in do_one_initcall() and _do_fork().
> 
> I don't think I'm really understanding.  Won't this produce the same
> value on each and every boot?

No, because of interrupts and intentional data races.

-- 
Emese