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Re: Linux xenfs vs privcmd
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jürgen Groß <jgross@xxxxxxxx>
- Date: Wed, 8 Oct 2025 16:49:14 +0200
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- Delivery-date: Wed, 08 Oct 2025 14:49:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.10.25 16:41, Andrew Cooper wrote:
On 08/10/2025 3:08 pm, Jürgen Groß wrote:
On 08.10.25 15:33, Andrew Cooper wrote:
Anyway - /dev/xen/privcmd (and /hypercall) shouldn't be tied to xenfs.
They should be SIF_PRIVILEGED alone, should they not?
I don't think they should be tied to SIF_PRIVILEGED, as device model ops
are handled via the privcmd driver, too.
TBH I have no idea why there is a direct connection to xenfs.
Did you try to modprobe privcmd without mounting xenfs? I guess the
connection is that the capabilities in /proc/xen/capabilities are
tested to
contain "control_d", resulting in the privcmd driver to be loaded.
modprobe xen_privcmd in isolation does cause /dev/xen/privcmd to appear.
Yes, I expected that.
So for removing xenfs there needs to be a way to find out that the system
is a Xen dom0. The easiest way would be to look into /sys/hypervisor/type
to contain "xen" and then /sys/hypervisor/start_flags/privileged to contain
"1".
Juergen
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