[PATCH v2 for-4.14 1/3] xen/monitor: Control register values

[Tamas K Lengyel <tamas@tklengyel.com>]

Extend the monitor_op domctl to include option that enables
controlling what values certain registers are permitted to hold
by a monitor subscriber.

Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
---
 xen/arch/x86/hvm/hvm.c       | 25 ++++++++++++++++---------
 xen/arch/x86/monitor.c       | 10 +++++++++-
 xen/include/asm-x86/domain.h |  1 +
 xen/include/public/domctl.h  |  1 +
 4 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 09ee299bc7..e6780c685b 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2263,7 +2263,8 @@ int hvm_set_cr0(unsigned long value, bool may_defer)
     {
         ASSERT(v->arch.vm_event);
 
-        if ( hvm_monitor_crX(CR0, value, old_value) )
+        if ( hvm_monitor_crX(CR0, value, old_value) &&
+             v->domain->arch.monitor.control_register_values )
         {
             /* The actual write will occur in hvm_do_resume(), if permitted. */
             v->arch.vm_event->write_data.do_write.cr0 = 1;
@@ -2362,7 +2363,8 @@ int hvm_set_cr3(unsigned long value, bool may_defer)
     {
         ASSERT(v->arch.vm_event);
 
-        if ( hvm_monitor_crX(CR3, value, old) )
+        if ( hvm_monitor_crX(CR3, value, old) &&
+             v->domain->arch.monitor.control_register_values )
         {
             /* The actual write will occur in hvm_do_resume(), if permitted. */
             v->arch.vm_event->write_data.do_write.cr3 = 1;
@@ -2443,7 +2445,8 @@ int hvm_set_cr4(unsigned long value, bool may_defer)
     {
         ASSERT(v->arch.vm_event);
 
-        if ( hvm_monitor_crX(CR4, value, old_cr) )
+        if ( hvm_monitor_crX(CR4, value, old_cr) &&
+             v->domain->arch.monitor.control_register_values )
         {
             /* The actual write will occur in hvm_do_resume(), if permitted. */
             v->arch.vm_event->write_data.do_write.cr4 = 1;
@@ -3587,13 +3590,17 @@ int hvm_msr_write_intercept(unsigned int msr, uint64_t msr_content,
 
         ASSERT(v->arch.vm_event);
 
-        /* The actual write will occur in hvm_do_resume() (if permitted). */
-        v->arch.vm_event->write_data.do_write.msr = 1;
-        v->arch.vm_event->write_data.msr = msr;
-        v->arch.vm_event->write_data.value = msr_content;
-
         hvm_monitor_msr(msr, msr_content, msr_old_content);
-        return X86EMUL_OKAY;
+
+        if ( v->domain->arch.monitor.control_register_values )
+        {
+            /* The actual write will occur in hvm_do_resume(), if permitted. */
+            v->arch.vm_event->write_data.do_write.msr = 1;
+            v->arch.vm_event->write_data.msr = msr;
+            v->arch.vm_event->write_data.value = msr_content;
+
+            return X86EMUL_OKAY;
+        }
     }
 
     if ( (ret = guest_wrmsr(v, msr, msr_content)) != X86EMUL_UNHANDLEABLE )
diff --git a/xen/arch/x86/monitor.c b/xen/arch/x86/monitor.c
index bbcb7536c7..1517a97f50 100644
--- a/xen/arch/x86/monitor.c
+++ b/xen/arch/x86/monitor.c
@@ -144,7 +144,15 @@ int arch_monitor_domctl_event(struct domain *d,
                               struct xen_domctl_monitor_op *mop)
 {
     struct arch_domain *ad = &d->arch;
-    bool requested_status = (XEN_DOMCTL_MONITOR_OP_ENABLE == mop->op);
+    bool requested_status;
+
+    if ( XEN_DOMCTL_MONITOR_OP_CONTROL_REGISTERS == mop->op )
+    {
+        ad->monitor.control_register_values = true;
+        return 0;
+    }
+
+    requested_status = (XEN_DOMCTL_MONITOR_OP_ENABLE == mop->op);
 
     switch ( mop->event )
     {
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 5b6d909266..d890ab7a22 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -416,6 +416,7 @@ struct arch_domain
          * This is used to filter out pagefaults.
          */
         unsigned int inguest_pagefault_disabled                            : 1;
+        unsigned int control_register_values                               : 1;
         struct monitor_msr_bitmap *msr_bitmap;
         uint64_t write_ctrlreg_mask[4];
     } monitor;
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 1ad34c35eb..cbcd25f12c 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -1025,6 +1025,7 @@ struct xen_domctl_psr_cmt_op {
 #define XEN_DOMCTL_MONITOR_OP_DISABLE           1
 #define XEN_DOMCTL_MONITOR_OP_GET_CAPABILITIES  2
 #define XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP  3
+#define XEN_DOMCTL_MONITOR_OP_CONTROL_REGISTERS 4
 
 #define XEN_DOMCTL_MONITOR_EVENT_WRITE_CTRLREG         0
 #define XEN_DOMCTL_MONITOR_EVENT_MOV_TO_MSR            1
-- 
2.26.1