Re: [PATCH 2/2] random: Account for entropy loss due to overwrites

From: H. Peter Anvin
Date: Thu Apr 25 2013 - 10:44:34 EST

On 04/25/2013 07:38 AM, Linus Torvalds wrote:
> This doesn't work AT ALL. You even hint at the reason why in your message.
> On Tue, Apr 23, 2013 at 9:26 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>> As such, this conservatism seems more than justified. Note, however,
>> that attempting to add one bit of entropy will never succeed; nor will
>> two bits unless the pool is completely empty. These roundoff
>> artifacts could be improved by using fixed-point arithmetic and adding
>> some number of fractional entropy bits.
> Take a look at "add_interrupt_randomness()". Hmm..


Right. Before July of last year add_interrupt_randomness() called
add_timer_randomness() which credits up to 11 bits, but not anymore.


OK, so we need to track fractional bits.


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