[Xen-devel] [PATCH v3 4/8] x86/vm_event/monitor/cr: check for vm-event subscriber on domctl

[Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>]

Enforce presence of a monitor vm-event subscriber when the toolstack user calls
xc_monitor_write_ctrlreg (XEN_DOMCTL_MONITOR_EVENT_WRITE_CTRLREG domctl).
Without this change, ASSERT(v->arch.vm_event) @ hvm_set_cr0 and such would fail
if the toolstack user calls xc_monitor_write_ctrlreg(...) w/ enable = true,
without first calling xc_monitor_enable().

Also adjust returned error code for similar check from -EINVAL to more
descriptive -ENOSYS (XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP).

Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/monitor.c        | 7 +++++++
 xen/include/asm-x86/monitor.h | 2 +-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/monitor.c b/xen/arch/x86/monitor.c
index 42f31bf..4d4db33 100644
--- a/xen/arch/x86/monitor.c
+++ b/xen/arch/x86/monitor.c
@@ -188,6 +188,13 @@ int arch_monitor_domctl_event(struct domain *d,
         unsigned int ctrlreg_bitmask;
         bool_t old_status;
 
+        /*
+         * Enabling cr-write vm-events without a vm_event subscriber is
+         * meaningless.
+         */
+        if ( !vm_event_domain_initialised(d) )
+            return -ENOSYS;
+
         /* sanity check: avoid left-shift undefined behavior */
         if ( unlikely(mop->u.mov_to_cr.index > 31) )
             return -EINVAL;
diff --git a/xen/include/asm-x86/monitor.h b/xen/include/asm-x86/monitor.h
index 9238ec8..2213124 100644
--- a/xen/include/asm-x86/monitor.h
+++ b/xen/include/asm-x86/monitor.h
@@ -52,7 +52,7 @@ int arch_monitor_domctl_op(struct domain *d, struct 
xen_domctl_monitor_op *mop)
         if ( vm_event_domain_initialised(d) )
             d->arch.mem_access_emulate_each_rep = !!mop->event;
         else
-            rc = -EINVAL;
+            rc = -ENOSYS;
 
         domain_unpause(d);
         break;
-- 
2.5.0


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel