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

On Wed, 2013-10-02 at 17:37 +0300, Gleb Natapov wrote:

On Wed, Oct 02, 2013 at 04:33:18PM +0200, Paolo Bonzini wrote:

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Il 02/10/2013 16:08, Alexander Graf ha scritto:

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The hwrng is accessible by host userspace via /dev/mem.

A guest should live on the same permission level as a user space
application. If you run QEMU as UID 1000 without access to /dev/mem, why
should the guest suddenly be able to directly access a memory location
(MMIO) it couldn't access directly through a normal user space interface.

It's basically a layering violation.

With Michael's earlier patch in this series, the hwrng is accessible by
host userspace via /dev/hwrng, no?

Access to which can be controlled by its permission. Permission of
/dev/kvm may be different. If we route hypercall via userspace and
configure qemu to get entropy from /dev/hwrng everything will fall
nicely together (except performance).

Yes, except abysmall performance and a lot more code for something
completely and utterly pointless .... nice.

Ben.