[Gllug] Letting Bohcs, UML or vmware have direct access to a PCI card or a SCSI device (not disk).

Nix nix at esperi.org.uk
Fri Sep 16 15:28:13 UTC 2005


On Fri, 16 Sep 2005, Russell Howe stipulated:
> On Fri, Sep 16, 2005 at 09:55:25AM +0100, Nix wrote:
>> That depends on whether the VM is executing non-privileged code. A VM
>> executing non-privileged code shouldn't allow that code to send
>> arbitrary SCSI commands.
> 
> Isn't the entire VM classed as 'unpriviledged code' by whatever
> container it's running in (e.g. the host kernel in the case of UML, or
> domain 0 in the case of Xen)?

That depends what the VM is for. You can run UMLs as root.

(Also, there's a tiny virtual machine in the kernel for interpreting
ACPI. That's as privileged as can be, with opcodes to do bus I/O.)

> At least, I'd say that's the case if the VM system is emulating a
> complete virtual machine.. with UML, I'd say the virtualisation boundary
> lies at the syscall level within the UML instance.

Yes. (In practice the distinction is hard to see.)

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 of a book whose author one wishes to insult.' --- Richard Dawkins
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