[Xen-devel] [PATCH 16/16] x86/monitor: fix: xc_monitor _write_ctrlreg w/o previous _enable must fail

[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(monitor_domain_initialised(v->domain));" @
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 -ENODEV (XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP).

Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/monitor.c        | 4 ++++
 xen/include/asm-x86/monitor.h | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/monitor.c b/xen/arch/x86/monitor.c
index 05a2f0d..4cf018a 100644
--- a/xen/arch/x86/monitor.c
+++ b/xen/arch/x86/monitor.c
@@ -324,6 +324,10 @@ int arch_monitor_domctl_event(struct domain *d,
         unsigned int ctrlreg_bitmask;
         bool_t old_status;
 
+        /* Meaningless without a monitor vm-events subscriber. */
+        if ( unlikely(!monitor_domain_initialised(d)) )
+            return -ENODEV;
+
         /* 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 11497ef..a6022db 100644
--- a/xen/include/asm-x86/monitor.h
+++ b/xen/include/asm-x86/monitor.h
@@ -47,7 +47,7 @@ int arch_monitor_domctl_op(struct domain *d, struct 
xen_domctl_monitor_op *mop)
         if ( likely(monitor_domain_initialised(d)) )
             d->arch.mem_access_emulate_each_rep = !!mop->event;
         else
-            rc = -EINVAL;
+            rc = -ENODEV;
 
         domain_unpause(d);
         break;
-- 
2.5.0


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