xen: enable altp2m at create domain domctl

Enabling it using an HVM param is fragile, and complicates the logic when
deciding whether options that interact with altp2m can also be enabled.

Leave the HVM param value for consumption by the guest, but prevent it from
being set.  Enabling is now done using and additional altp2m specific field in
xen_domctl_createdomain.

Note that albeit only currently implemented in x86, altp2m could be implemented
in other architectures, hence why the field is added to xen_domctl_createdomain
instead of xen_arch_domainconfig.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com> # hypervisor
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com> # tools/libs/
Release-acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

tools/libs/light/libxl_create.c

@@ -372,7 +372,6 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
         libxl_defbool_setdefault(&b_info->u.hvm.viridian,           false);
         libxl_defbool_setdefault(&b_info->u.hvm.hpet,               true);
         libxl_defbool_setdefault(&b_info->u.hvm.vpt_align,          true);
-        libxl_defbool_setdefault(&b_info->u.hvm.altp2m,             false);
         libxl_defbool_setdefault(&b_info->u.hvm.usb,                false);
         libxl_defbool_setdefault(&b_info->u.hvm.vkb_device,         true);
         libxl_defbool_setdefault(&b_info->u.hvm.xen_platform_pci,   true);
@@ -678,6 +677,28 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
         if (info->passthrough == LIBXL_PASSTHROUGH_SYNC_PT)
             create.iommu_opts |= XEN_DOMCTL_IOMMU_no_sharept;
 
+        LOG(DETAIL, "altp2m: %s", libxl_altp2m_mode_to_string(b_info->altp2m));
+        switch(b_info->altp2m) {
+        case LIBXL_ALTP2M_MODE_MIXED:
+            create.altp2m_opts |=
+                XEN_DOMCTL_ALTP2M_mode(XEN_DOMCTL_ALTP2M_mixed);
+            break;
+
+        case LIBXL_ALTP2M_MODE_EXTERNAL:
+            create.altp2m_opts |=
+                XEN_DOMCTL_ALTP2M_mode(XEN_DOMCTL_ALTP2M_external);
+            break;
+
+        case LIBXL_ALTP2M_MODE_LIMITED:
+            create.altp2m_opts |=
+                XEN_DOMCTL_ALTP2M_mode(XEN_DOMCTL_ALTP2M_limited);
+            break;
+
+        case LIBXL_ALTP2M_MODE_DISABLED:
+            /* Nothing to do - altp2m disabled is signaled as mode == 0. */
+            break;
+        }
+
         /* Ultimately, handle is an array of 16 uint8_t, same as uuid */
         libxl_uuid_copy(ctx, (libxl_uuid *)&create.handle, &info->uuid);
 

tools/libs/light/libxl_x86.c

@@ -407,19 +407,9 @@ static int hvm_set_conf_params(libxl__gc *gc, uint32_t domid,
     libxl_ctx *ctx = libxl__gc_owner(gc);
     xc_interface *xch = ctx->xch;
     int ret = ERROR_FAIL;
-    unsigned int altp2m = info->altp2m;
 
     switch(info->type) {
     case LIBXL_DOMAIN_TYPE_HVM:
-        /* The config parameter "altp2m" replaces the parameter "altp2mhvm". For
-         * legacy reasons, both parameters are accepted on x86 HVM guests.
-         *
-         * If the legacy field info->u.hvm.altp2m is set, activate altp2m.
-         * Otherwise set altp2m based on the field info->altp2m. */
-        if (info->altp2m == LIBXL_ALTP2M_MODE_DISABLED &&
-            libxl_defbool_val(info->u.hvm.altp2m))
-            altp2m = libxl_defbool_val(info->u.hvm.altp2m);
-
         if (xc_hvm_param_set(xch, domid, HVM_PARAM_HPET_ENABLED,
                              libxl_defbool_val(info->u.hvm.hpet))) {
             LOG(ERROR, "Couldn't set HVM_PARAM_HPET_ENABLED");
@@ -444,10 +434,6 @@ static int hvm_set_conf_params(libxl__gc *gc, uint32_t domid,
             LOG(ERROR, "Couldn't set HVM_PARAM_TIMER_MODE");
             goto out;
         }
-        if (xc_hvm_param_set(xch, domid, HVM_PARAM_ALTP2M, altp2m)) {
-            LOG(ERROR, "Couldn't set HVM_PARAM_ALTP2M");
-            goto out;
-        }
         break;
 
     default:
@@ -818,6 +804,18 @@ int libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
     libxl_defbool_setdefault(&b_info->acpi, true);
     libxl_defbool_setdefault(&b_info->arch_x86.msr_relaxed, false);
 
+    /*
+     * The config parameter "altp2m" replaces the parameter "altp2mhvm".
+     * For legacy reasons, both parameters are accepted on x86 HVM guests.
+     *
+     * If the legacy field info->u.hvm.altp2m is set, activate altp2m.
+     * Otherwise set altp2m based on the field info->altp2m.
+     */
+    libxl_defbool_setdefault(&b_info->u.hvm.altp2m, false);
+    if (b_info->altp2m == LIBXL_ALTP2M_MODE_DISABLED &&
+        libxl_defbool_val(b_info->u.hvm.altp2m))
+        b_info->altp2m = libxl_defbool_val(b_info->u.hvm.altp2m);
+
     return 0;
 }
 

tools/ocaml/libs/xc/xenctrl_stubs.c

@@ -257,7 +257,7 @@ CAMLprim value stub_xc_domain_create(value xch_val, value wanted_domid, value co
 #if defined(__i386__) || defined(__x86_64__)
 
 		/* Quick & dirty check for ABI changes. */
-		BUILD_BUG_ON(sizeof(cfg) != 64);
+		BUILD_BUG_ON(sizeof(cfg) != 68);
 
         /* Mnemonics for the named fields inside xen_x86_arch_domainconfig */
 #define VAL_EMUL_FLAGS          Field(arch_domconfig, 0)

xen/arch/arm/domain.c

@@ -688,6 +688,12 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
         return -EINVAL;
     }
 
+    if ( config->altp2m_opts )
+    {
+        dprintk(XENLOG_INFO, "Altp2m not supported\n");
+        return -EINVAL;
+    }
+
     return 0;
 }
 

xen/arch/x86/domain.c

@@ -637,6 +637,8 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
     bool hap = config->flags & XEN_DOMCTL_CDF_hap;
     bool nested_virt = config->flags & XEN_DOMCTL_CDF_nested_virt;
     unsigned int max_vcpus;
+    unsigned int altp2m_mode = MASK_EXTR(config->altp2m_opts,
+                                         XEN_DOMCTL_ALTP2M_mode_mask);
 
     if ( hvm ? !hvm_enabled : !IS_ENABLED(CONFIG_PV) )
     {
@@ -715,6 +717,26 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
         return -EINVAL;
     }
 
+    if ( config->altp2m_opts & ~XEN_DOMCTL_ALTP2M_mode_mask )
+    {
+        dprintk(XENLOG_INFO, "Invalid altp2m options selected: %#x\n",
+                config->flags);
+        return -EINVAL;
+    }
+
+    if ( altp2m_mode && nested_virt )
+    {
+        dprintk(XENLOG_INFO,
+                "Nested virt and altp2m are not supported together\n");
+        return -EINVAL;
+    }
+
+    if ( altp2m_mode && !hap )
+    {
+        dprintk(XENLOG_INFO, "altp2m is only supported with HAP\n");
+        return -EINVAL;
+    }
+
     return 0;
 }
 

xen/arch/x86/hvm/hvm.c

@@ -658,6 +658,22 @@ int hvm_domain_initialise(struct domain *d,
 
     d->arch.hvm.params[HVM_PARAM_TRIPLE_FAULT_REASON] = SHUTDOWN_reboot;
 
+    /* Set altp2m based on domctl flags. */
+    switch ( MASK_EXTR(config->altp2m_opts, XEN_DOMCTL_ALTP2M_mode_mask) )
+    {
+    case XEN_DOMCTL_ALTP2M_mixed:
+        d->arch.hvm.params[HVM_PARAM_ALTP2M] = XEN_ALTP2M_mixed;
+        break;
+
+    case XEN_DOMCTL_ALTP2M_external:
+        d->arch.hvm.params[HVM_PARAM_ALTP2M] = XEN_ALTP2M_external;
+        break;
+
+    case XEN_DOMCTL_ALTP2M_limited:
+        d->arch.hvm.params[HVM_PARAM_ALTP2M] = XEN_ALTP2M_limited;
+        break;
+    }
+
     vpic_init(d);
 
     rc = vioapic_init(d);
@@ -4166,6 +4182,12 @@ static int hvm_allow_set_param(struct domain *d,
     case HVM_PARAM_CONSOLE_EVTCHN:
     case HVM_PARAM_X87_FIP_WIDTH:
         break;
+
+    /* The following parameters are read-only. */
+    case HVM_PARAM_ALTP2M:
+        rc = -EEXIST;
+        break;
+
     /* The following parameters are deprecated. */
     case HVM_PARAM_PAE_ENABLED:
     case HVM_PARAM_DM_DOMAIN:
@@ -4207,7 +4229,6 @@ static int hvm_allow_set_param(struct domain *d,
     case HVM_PARAM_BUFIOREQ_PFN:
     case HVM_PARAM_IOREQ_SERVER_PFN:
     case HVM_PARAM_NR_IOREQ_SERVER_PAGES:
-    case HVM_PARAM_ALTP2M:
     case HVM_PARAM_MCA_CAP:
         if ( value != 0 && new_value != value )
             rc = -EEXIST;

xen/include/public/domctl.h

@@ -86,6 +86,24 @@ struct xen_domctl_createdomain {
 
     uint32_t grant_opts;
 
+/*
+ * Enable altp2m mixed mode.
+ *
+ * Note that 'mixed' mode has not been evaluated for safety from a security
+ * perspective.  Before using this mode in a security-critical environment,
+ * each subop should be evaluated for safety, with unsafe subops blacklisted in
+ * XSM.
+ */
+#define XEN_DOMCTL_ALTP2M_mixed      (1U)
+/* Enable altp2m external mode. */
+#define XEN_DOMCTL_ALTP2M_external   (2U)
+/* Enable altp2m limited mode. */
+#define XEN_DOMCTL_ALTP2M_limited    (3U)
+/* Altp2m mode signaling uses bits [0, 1]. */
+#define XEN_DOMCTL_ALTP2M_mode_mask  (0x3U)
+#define XEN_DOMCTL_ALTP2M_mode(m)    ((m) & XEN_DOMCTL_ALTP2M_mode_mask)
+    uint32_t altp2m_opts;
+
     /* Per-vCPU buffer size in bytes.  0 to disable. */
     uint32_t vmtrace_size;
 

xen/include/public/hvm/params.h

@@ -246,16 +246,11 @@
 #define HVM_PARAM_VM_GENERATION_ID_ADDR 34
 
 /*
- * Set mode for altp2m:
- *  disabled: don't activate altp2m (default)
+ * Get mode for altp2m:
+ *  disabled: altp2m not active (default)
  *  mixed: allow access to all altp2m ops for both in-guest and external tools
  *  external: allow access to external privileged tools only
  *  limited: guest only has limited access (ie. control VMFUNC and #VE)
- *
- * Note that 'mixed' mode has not been evaluated for safety from a
- * security perspective.  Before using this mode in a
- * security-critical environment, each subop should be evaluated for
- * safety, with unsafe subops blacklisted in XSM.
  */
 #define HVM_PARAM_ALTP2M       35
 #define XEN_ALTP2M_disabled      0