Hi Julien,
Thanks for taking a look.
On 2025-07-21 13:58, Julien Grall wrote:
Hi Jason,
On 16/07/2025 22:14, Jason Andryuk wrote:
Add a new create domain flag to indicate if a domain can be the target
of hypercalls. By default all domains can be targetted - subject to any
other permission checks.
This property is useful in a safety environment to isolate domains for
freedom from interference.
I see the flag is exposed to the toolstack. However, I don't see how you
can successfully create a VM if you are not allowed to call hypercalls
(for instance to add some memory).
Yes, you are right. With dom0less/Hyperlaunch, I'd not been considering
the toolstack.
I think, at minimum, you would want to allow hypercalls while the domain
is created. That said, I wonder if this setup would not be better to
describe with XSM?
Re-labeling with Flask would allow different permissions between
building and running. domain_unpause would need to be allowed, but that
doesn't stop a domain.
At first glance, like you say, the untargetable property could be
enabled when domain creation finishes.
[...]
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 88a294c5be..f1f6f96bc2 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -70,9 +70,11 @@ struct xen_domctl_createdomain {
#define XEN_DOMCTL_CDF_trap_unmapped_accesses (1U << 8)
/* Allow domain to provide device model for multiple other domains */
#define XEN_DOMCTL_CDF_device_model (1U << 9)
+/* Domain cannot be the target of hypercalls */
+#define XEN_DOMCTL_CDF_not_hypercall_target (1U << 10)
/* Max XEN_DOMCTL_CDF_* constant. Used for ABI checking. */
-#define XEN_DOMCTL_CDF_MAX XEN_DOMCTL_CDF_device_model
+#define XEN_DOMCTL_CDF_MAX XEN_DOMCTL_CDF_not_hypercall_target
I am not sure where to comment. But aren't both flags mutually exclusive?
No, XEN_DOMCTL_CDF_device_model is *this* domain providing the device
model to other domains:
+ * Device model capability allows the use of the dm_op hypercalls to
provide
+ * the device model emulation (run QEMU) for other domains. This is a
+ * subset of the Control capability which can be granted to the
+ * Hardware domain for running QEMU.
Whereas XEN_DOMCTL_CDF_not_hypercall_target removes targeting on *this*
domain. So the domain with XEN_DOMCTL_CDF_device_model cannot target
the XEN_DOMCTL_CDF_not_hypercall_target domain.
Regards,
Jason
