linux-kernel - Re: [PATCH 3/3] KVM: PPC: Book3S: Add support for hwrng found on some powernv systems

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Date:	Wed, 02 Oct 2013 16:38:19 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Alexander Graf <agraf@...e.de>
CC:	Michael Ellerman <michael@...erman.id.au>,
	Gleb Natapov <gleb@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linux-kernel@...r.kernel.org, mpm@...enic.com,
	herbert@...dor.hengli.com.au, linuxppc-dev@...abs.org,
	kvm@...r.kernel.org, kvm-ppc@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 3/3] KVM: PPC: Book3S: Add support for hwrng found on
 some powernv systems

Il 02/10/2013 16:36, Alexander Graf ha scritto:
>> > 
>> > With Michael's earlier patch in this series, the hwrng is accessible by
>> > host userspace via /dev/hwrng, no?
> Yes, but there's not token from user space that gets passed into the
> kernel to check whether access is ok or not. So while QEMU may not have
> permission to open /dev/hwrng it could spawn a guest that opens it,
> drains all entropy out of it and thus stall other processes which try to
> fetch entropy, no?
> 
> Maybe I haven't fully grasped the interface yet though :).

Yes, that's right.  I don't think it's a huge problem, but it's another
point in favor of just doing the hypercall in userspace.

Paolo
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