x86/altp2m: hypercall to set altp2m view visibility

At this moment a guest can call vmfunc to change the altp2m view. This
should be limited in order to avoid any unwanted view switch.

The new xc_altp2m_set_visibility() solves this by making views invisible
to vmfunc.
This is done by having a separate arch.altp2m_working_eptp that is
populated and made invalid in the same places as altp2m_eptp. This is
written to EPTP_LIST_ADDR.
The views are made in/visible by marking them with INVALID_MFN or
copying them back from altp2m_eptp.
To have consistency the visibility also applies to
p2m_switch_domain_altp2m_by_id().

The usage of this hypercall is aimed at dom0 having a logic with a number of views
created and at some time there is a need to be sure that only some of the views
can be switched, saving the rest and making them visible when the time
is right.

Note: If altp2m mode is set to mixed the guest is able to change the view
visibility and then call vmfunc.

Signed-off-by: Alexandru Isaila <aisaila@bitdefender.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Wei Liu <wl@xen.org>

tools/libxc/include/xenctrl.h

@@ -1943,6 +1943,13 @@ int xc_altp2m_change_gfn(xc_interface *handle, uint32_t domid,
                          xen_pfn_t new_gfn);
 int xc_altp2m_get_vcpu_p2m_idx(xc_interface *handle, uint32_t domid,
                                uint32_t vcpuid, uint16_t *p2midx);
+/*
+ * Set view visibility for xc_altp2m_switch_to_view and vmfunc.
+ * Note: If altp2m mode is set to mixed the guest is able to change the view
+ * visibility and then call vmfunc.
+ */
+int xc_altp2m_set_visibility(xc_interface *handle, uint32_t domid,
+                             uint16_t view_id, bool visible);
 
 /** 
  * Mem paging operations.

tools/libxc/xc_altp2m.c

@@ -410,3 +410,27 @@ int xc_altp2m_get_vcpu_p2m_idx(xc_interface *handle, uint32_t domid,
     xc_hypercall_buffer_free(handle, arg);
     return rc;
 }
+
+int xc_altp2m_set_visibility(xc_interface *handle, uint32_t domid,
+                             uint16_t view_id, bool visible)
+{
+    int rc;
+
+    DECLARE_HYPERCALL_BUFFER(xen_hvm_altp2m_op_t, arg);
+
+    arg = xc_hypercall_buffer_alloc(handle, arg, sizeof(*arg));
+    if ( arg == NULL )
+        return -1;
+
+    arg->version = HVMOP_ALTP2M_INTERFACE_VERSION;
+    arg->cmd = HVMOP_altp2m_set_visibility;
+    arg->domain = domid;
+    arg->u.set_visibility.altp2m_idx = view_id;
+    arg->u.set_visibility.visible = visible;
+
+    rc = xencall2(handle->xcall, __HYPERVISOR_hvm_op, HVMOP_altp2m,
+                  HYPERCALL_BUFFER_AS_ARG(arg));
+
+    xc_hypercall_buffer_free(handle, arg);
+    return rc;
+}

xen/arch/x86/hvm/hvm.c

@@ -4509,6 +4509,7 @@ static int do_altp2m_op(
     case HVMOP_altp2m_get_mem_access:
     case HVMOP_altp2m_change_gfn:
     case HVMOP_altp2m_get_p2m_idx:
+    case HVMOP_altp2m_set_visibility:
         break;
 
     default:
@@ -4786,6 +4787,19 @@ static int do_altp2m_op(
         break;
     }
 
+    case HVMOP_altp2m_set_visibility:
+    {
+        unsigned int idx = a.u.set_visibility.altp2m_idx;
+
+        if ( a.u.set_visibility.pad )
+            rc = -EINVAL;
+        else if ( !altp2m_active(d) )
+            rc = -EOPNOTSUPP;
+        else
+            rc = p2m_set_altp2m_view_visibility(d, idx,
+                                                a.u.set_visibility.visible);
+    }
+
     default:
         ASSERT_UNREACHABLE();
     }

xen/arch/x86/hvm/vmx/vmx.c

@@ -2140,7 +2140,7 @@ static void vmx_vcpu_update_vmfunc_ve(struct vcpu *v)
     {
         v->arch.hvm.vmx.secondary_exec_control |= mask;
         __vmwrite(VM_FUNCTION_CONTROL, VMX_VMFUNC_EPTP_SWITCHING);
-        __vmwrite(EPTP_LIST_ADDR, virt_to_maddr(d->arch.altp2m_eptp));
+        __vmwrite(EPTP_LIST_ADDR, virt_to_maddr(d->arch.altp2m_visible_eptp));
 
         if ( cpu_has_vmx_virt_exceptions )
         {

xen/arch/x86/mm/hap/hap.c

@@ -492,8 +492,17 @@ int hap_enable(struct domain *d, u32 mode)
             goto out;
         }
 
+        if ( (d->arch.altp2m_visible_eptp = alloc_xenheap_page()) == NULL )
+        {
+            rv = -ENOMEM;
+            goto out;
+        }
+
         for ( i = 0; i < MAX_EPTP; i++ )
+        {
             d->arch.altp2m_eptp[i] = mfn_x(INVALID_MFN);
+            d->arch.altp2m_visible_eptp[i] = mfn_x(INVALID_MFN);
+        }
 
         for ( i = 0; i < MAX_ALTP2M; i++ )
         {
@@ -527,6 +536,12 @@ void hap_final_teardown(struct domain *d)
             d->arch.altp2m_eptp = NULL;
         }
 
+        if ( d->arch.altp2m_visible_eptp )
+        {
+            free_xenheap_page(d->arch.altp2m_visible_eptp);
+            d->arch.altp2m_visible_eptp = NULL;
+        }
+
         for ( i = 0; i < MAX_ALTP2M; i++ )
             p2m_teardown(d->arch.altp2m_p2m[i]);
     }

xen/arch/x86/mm/p2m-ept.c

@@ -1368,6 +1368,7 @@ void p2m_init_altp2m_ept(struct domain *d, unsigned int i)
     ept = &p2m->ept;
     ept->mfn = pagetable_get_pfn(p2m_get_pagetable(p2m));
     d->arch.altp2m_eptp[array_index_nospec(i, MAX_EPTP)] = ept->eptp;
+    d->arch.altp2m_visible_eptp[array_index_nospec(i, MAX_EPTP)] = ept->eptp;
 }
 
 unsigned int p2m_find_altp2m_by_eptp(struct domain *d, uint64_t eptp)

xen/arch/x86/mm/p2m.c

@@ -2533,6 +2533,7 @@ void p2m_flush_altp2m(struct domain *d)
     {
         p2m_reset_altp2m(d, i, ALTP2M_DEACTIVATE);
         d->arch.altp2m_eptp[i] = mfn_x(INVALID_MFN);
+        d->arch.altp2m_visible_eptp[i] = mfn_x(INVALID_MFN);
     }
 
     altp2m_list_unlock(d);
@@ -2652,7 +2653,9 @@ int p2m_destroy_altp2m_by_id(struct domain *d, unsigned int idx)
         {
             p2m_reset_altp2m(d, idx, ALTP2M_DEACTIVATE);
             d->arch.altp2m_eptp[array_index_nospec(idx, MAX_EPTP)] =
-            mfn_x(INVALID_MFN);
+                mfn_x(INVALID_MFN);
+            d->arch.altp2m_visible_eptp[array_index_nospec(idx, MAX_EPTP)] =
+                mfn_x(INVALID_MFN);
             rc = 0;
         }
     }
@@ -2679,7 +2682,7 @@ int p2m_switch_domain_altp2m_by_id(struct domain *d, unsigned int idx)
     rc = -EINVAL;
     altp2m_list_lock(d);
 
-    if ( d->arch.altp2m_eptp[idx] != mfn_x(INVALID_MFN) )
+    if ( d->arch.altp2m_visible_eptp[idx] != mfn_x(INVALID_MFN) )
     {
         for_each_vcpu( d, v )
             if ( idx != vcpu_altp2m(v).p2midx )
@@ -3163,6 +3166,33 @@ int p2m_get_suppress_ve(struct domain *d, gfn_t gfn, bool *suppress_ve,
 
     return rc;
 }
+
+int p2m_set_altp2m_view_visibility(struct domain *d, unsigned int altp2m_idx,
+                                   uint8_t visible)
+{
+    int rc = 0;
+
+    altp2m_list_lock(d);
+
+    /*
+     * Eptp index is correlated with altp2m index and should not exceed
+     * min(MAX_ALTP2M, MAX_EPTP).
+     */
+    if ( altp2m_idx >= min(ARRAY_SIZE(d->arch.altp2m_p2m), MAX_EPTP) ||
+         d->arch.altp2m_eptp[array_index_nospec(altp2m_idx, MAX_EPTP)] ==
+         mfn_x(INVALID_MFN) )
+        rc = -EINVAL;
+    else if ( visible )
+        d->arch.altp2m_visible_eptp[array_index_nospec(altp2m_idx, MAX_EPTP)] =
+            d->arch.altp2m_eptp[array_index_nospec(altp2m_idx, MAX_EPTP)];
+    else
+        d->arch.altp2m_visible_eptp[array_index_nospec(altp2m_idx, MAX_EPTP)] =
+            mfn_x(INVALID_MFN);
+
+    altp2m_list_unlock(d);
+
+    return rc;
+}
 #endif
 
 /*

xen/include/asm-x86/domain.h

@@ -327,6 +327,7 @@ struct arch_domain
     struct p2m_domain *altp2m_p2m[MAX_ALTP2M];
     mm_lock_t altp2m_list_lock;
     uint64_t *altp2m_eptp;
+    uint64_t *altp2m_visible_eptp;
 #endif
 
     /* NB. protected by d->event_lock and by irq_desc[irq].lock */

xen/include/asm-x86/p2m.h

@@ -898,6 +898,10 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned int idx,
 int p2m_altp2m_propagate_change(struct domain *d, gfn_t gfn,
                                 mfn_t mfn, unsigned int page_order,
                                 p2m_type_t p2mt, p2m_access_t p2ma);
+
+/* Set a specific p2m view visibility */
+int p2m_set_altp2m_view_visibility(struct domain *d, unsigned int idx,
+                                   uint8_t visible);
 #else
 struct p2m_domain *p2m_get_altp2m(struct vcpu *v);
 static inline void p2m_altp2m_check(struct vcpu *v, uint16_t idx) {}

xen/include/public/hvm/hvm_op.h

@@ -318,6 +318,12 @@ struct xen_hvm_altp2m_get_vcpu_p2m_idx {
     uint16_t altp2m_idx;
 };
 
+struct xen_hvm_altp2m_set_visibility {
+    uint16_t altp2m_idx;
+    uint8_t visible;
+    uint8_t pad;
+};
+
 struct xen_hvm_altp2m_op {
     uint32_t version;   /* HVMOP_ALTP2M_INTERFACE_VERSION */
     uint32_t cmd;
@@ -350,6 +356,8 @@ struct xen_hvm_altp2m_op {
 #define HVMOP_altp2m_get_p2m_idx          14
 /* Set the "Supress #VE" bit for a range of pages */
 #define HVMOP_altp2m_set_suppress_ve_multi 15
+/* Set visibility for a given altp2m view */
+#define HVMOP_altp2m_set_visibility       16
     domid_t domain;
     uint16_t pad1;
     uint32_t pad2;
@@ -367,6 +375,7 @@ struct xen_hvm_altp2m_op {
         struct xen_hvm_altp2m_suppress_ve_multi    suppress_ve_multi;
         struct xen_hvm_altp2m_vcpu_disable_notify  disable_notify;
         struct xen_hvm_altp2m_get_vcpu_p2m_idx     get_vcpu_p2m_idx;
+        struct xen_hvm_altp2m_set_visibility       set_visibility;
         uint8_t pad[64];
     } u;
 };