On 02.10.2013, at 16:33, Paolo Bonzini wrote:

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

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

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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

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should the guest suddenly be able to directly access a memory =

location

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(MMIO) it couldn't access directly through a normal user space =

interface.

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It's basically a layering violation.

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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 :).


Alex