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Message-ID: <20160606133801.GA6136@davidb.org>
Date: Mon, 6 Jun 2016 07:38:01 -0600
From: David Brown <david.brown@...aro.org>
To: kernel-hardening@...ts.openwall.com
Cc: Andrew Morton <akpm@...ux-foundation.org>, 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: Re: [PATCH v2 1/3] Add the latent_entropy gcc
plugin
On Fri, Jun 03, 2016 at 07:42:52PM +0200, Emese Revfy wrote:
>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.
Wouldn't that result in the value having one of a small number of
values, then? Even if it was just one of thousands or millions of
values, it would make the search space quite small.
David
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