Re: [RFD] Direct support for the x86 RDRAND instruction

[Jeff Garzik]

On 07/29/2011 04:37 PM, H. Peter Anvin wrote:
> From: "H. Peter Anvin"<hpa@xxxxxxxxxxxxxxx>
>
> This is a proposed patchset to enable the new x86 RDRAND instruction,
> labelled "Bull Mountain Technology" by Intel.  It is a different beast
> than any other hardware random number generator that I have personally
> encountered: it is not just a random number source, but contains a
> high bandwidth random number generator, an AES cryptographic whitener,
> and integrity monitoring all in hardware.
>
> For technical documentation see:
>
> http://software.intel.com/en-us/articles/download-the-latest-bull-mountain-software-implementation-guide/
>
> This proposed patchset enables RDRAND bypass for current users of the
> nonblocking random pool (that is, for /dev/urandom and its equvalent
> in-kernel users) but not for the blocking pool (/dev/random).  This is
> because RDRAND, although reseeded way more frequently than what is
> practical to do in software, is technically a nonblocking source that
> can behave as a PRNG.  It can be used as a source for randomness for
> /dev/random, but that is not addressed by this patchset.

This does not cover the one question I [predictably] have:  why not do 
this in rngd, rather than the kernel?

Since many (all?) TPM chips include a random number generator, Dell has 
made sure that most distros have a useful copy of the rng-tools 
userspace pkg I've been maintaining.

It would seem straightforward to add this to rngd, and enable RDRAND on 
older distros and kernels, as well as current distros / kernels.  This 
also gets useful entropy to /dev/random as part of normal operation, 
rather than only merely speeding up /dev/urandom.

Though for the record, I do agree that this is a nice, small and clean 
kernel implementation.

	Jeff




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