linux-kernel - Re: [PATCH] random: mix all saved registers into entropy pool

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <537A8E22.4030400@zytor.com>
Date:	Mon, 19 May 2014 16:05:06 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jörn Engel <joern@...fs.org>
CC:	"Theodore Ts'o" <tytso@....edu>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] random: mix all saved registers into entropy pool

On 05/19/2014 03:39 PM, Jörn Engel wrote:
> On Mon, 19 May 2014 15:18:01 -0700, H. Peter Anvin wrote:
>>
>> I think this is likely to be particularly valuable during boot.  I can
>> see it becoming substantially less valuable after that point, but during
>> boot is when the most critical.
>>
>> What I do see as an issue is that the value is probably impossible to
>> quantify, and so I feel more than a bit queasy about giving it
>> /dev/random credit.  However, making sure the pool is well stirred
>> during boot is really way more important.
> 
> I would feel fairly confident giving this .25 bits of entropy per
> event.  With 40% unique hashes and assuming at most 1 bit of entropy
> for a unique hash, that is a fairly conservative underestimate.
> 

Sure, but that is for a specific workload.

> What worries me is that much of those 5s may be spent inside the idle
> loop and have rather predictable register content and we may run
> tickless.  I have no great solution for that case.
>
> We could change the ratelimiting to, say, 4 interrupts per jiffie.
> But that would still not help much in the worst case scenario above,
> so the benefits don't seem convincing.

Exactly.

	-hpa

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/