hw/arm/virt: dt: add rng-seed property

In 60592cfed2 ("hw/arm/virt: dt: add kaslr-seed property"), the
kaslr-seed property was added, but the equally as important rng-seed
property was forgotten about, which has identical semantics for a
similar purpose. This commit implements it in exactly the same way as
kaslr-seed. It then changes the name of the disabling option to reflect
that this has more to do with randomness vs determinism, rather than
something particular about kaslr.

Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
[PMM: added deprecated.rst section for the deprecation]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/about/deprecated.rst

@@ -225,6 +225,14 @@ Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.
 System emulator machines
 ------------------------
 
+Arm ``virt`` machine ``dtb-kaslr-seed`` property
+''''''''''''''''''''''''''''''''''''''''''''''''
+
+The ``dtb-kaslr-seed`` property on the ``virt`` board has been
+deprecated; use the new name ``dtb-randomness`` instead. The new name
+better reflects the way this property affects all random data within
+the device tree blob, not just the ``kaslr-seed`` node.
+
 PPC 405 ``taihu`` machine (since 7.0)
 '''''''''''''''''''''''''''''''''''''
 

docs/system/arm/virt.rst

@@ -126,13 +126,18 @@ ras
   Set ``on``/``off`` to enable/disable reporting host memory errors to a guest
   using ACPI and guest external abort exceptions. The default is off.
 
+dtb-randomness
+  Set ``on``/``off`` to pass random seeds via the guest DTB
+  rng-seed and kaslr-seed nodes (in both "/chosen" and
+  "/secure-chosen") to use for features like the random number
+  generator and address space randomisation. The default is
+  ``on``. You will want to disable it if your trusted boot chain
+  will verify the DTB it is passed, since this option causes the
+  DTB to be non-deterministic. It would be the responsibility of
+  the firmware to come up with a seed and pass it on if it wants to.
+
 dtb-kaslr-seed
-  Set ``on``/``off`` to pass a random seed via the guest dtb
+  A deprecated synonym for dtb-randomness.
-  kaslr-seed node (in both "/chosen" and /secure-chosen) to use
-  for features like address space randomisation. The default is
-  ``on``. You will want to disable it if your trusted boot chain will
-  verify the DTB it is passed. It would be the responsibility of the
-  firmware to come up with a seed and pass it on if it wants to.
 
 Linux guest kernel configuration
 """"""""""""""""""""""""""""""""

hw/arm/virt.c

@@ -221,14 +221,18 @@ static bool cpu_type_valid(const char *cpu)
     return false;
 }
 
-static void create_kaslr_seed(MachineState *ms, const char *node)
+static void create_randomness(MachineState *ms, const char *node)
 {
-    uint64_t seed;
+    struct {
+        uint64_t kaslr;
+        uint8_t rng[32];
+    } seed;
 
     if (qemu_guest_getrandom(&seed, sizeof(seed), NULL)) {
         return;
     }
-    qemu_fdt_setprop_u64(ms->fdt, node, "kaslr-seed", seed);
+    qemu_fdt_setprop_u64(ms->fdt, node, "kaslr-seed", seed.kaslr);
+    qemu_fdt_setprop(ms->fdt, node, "rng-seed", seed.rng, sizeof(seed.rng));
 }
 
 static void create_fdt(VirtMachineState *vms)
@@ -251,14 +255,14 @@ static void create_fdt(VirtMachineState *vms)
 
     /* /chosen must exist for load_dtb to fill in necessary properties later */
     qemu_fdt_add_subnode(fdt, "/chosen");
-    if (vms->dtb_kaslr_seed) {
+    if (vms->dtb_randomness) {
-        create_kaslr_seed(ms, "/chosen");
+        create_randomness(ms, "/chosen");
     }
 
     if (vms->secure) {
         qemu_fdt_add_subnode(fdt, "/secure-chosen");
-        if (vms->dtb_kaslr_seed) {
+        if (vms->dtb_randomness) {
-            create_kaslr_seed(ms, "/secure-chosen");
+            create_randomness(ms, "/secure-chosen");
         }
     }
 
@@ -2340,18 +2344,18 @@ static void virt_set_its(Object *obj, bool value, Error **errp)
     vms->its = value;
 }
 
-static bool virt_get_dtb_kaslr_seed(Object *obj, Error **errp)
+static bool virt_get_dtb_randomness(Object *obj, Error **errp)
 {
     VirtMachineState *vms = VIRT_MACHINE(obj);
 
-    return vms->dtb_kaslr_seed;
+    return vms->dtb_randomness;
 }
 
-static void virt_set_dtb_kaslr_seed(Object *obj, bool value, Error **errp)
+static void virt_set_dtb_randomness(Object *obj, bool value, Error **errp)
 {
     VirtMachineState *vms = VIRT_MACHINE(obj);
 
-    vms->dtb_kaslr_seed = value;
+    vms->dtb_randomness = value;
 }
 
 static char *virt_get_oem_id(Object *obj, Error **errp)
@@ -2980,12 +2984,18 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
                                           "Set on/off to enable/disable "
                                           "ITS instantiation");
 
+    object_class_property_add_bool(oc, "dtb-randomness",
+                                   virt_get_dtb_randomness,
+                                   virt_set_dtb_randomness);
+    object_class_property_set_description(oc, "dtb-randomness",
+                                          "Set off to disable passing random or "
+                                          "non-deterministic dtb nodes to guest");
+
     object_class_property_add_bool(oc, "dtb-kaslr-seed",
-                                   virt_get_dtb_kaslr_seed,
+                                   virt_get_dtb_randomness,
-                                   virt_set_dtb_kaslr_seed);
+                                   virt_set_dtb_randomness);
     object_class_property_set_description(oc, "dtb-kaslr-seed",
-                                          "Set off to disable passing of kaslr-seed "
+                                          "Deprecated synonym of dtb-randomness");
-                                          "dtb node to guest");
 
     object_class_property_add_str(oc, "x-oem-id",
                                   virt_get_oem_id,
@@ -3053,8 +3063,8 @@ static void virt_instance_init(Object *obj)
     /* MTE is disabled by default.  */
     vms->mte = false;
 
-    /* Supply a kaslr-seed by default */
+    /* Supply kaslr-seed and rng-seed by default */
-    vms->dtb_kaslr_seed = true;
+    vms->dtb_randomness = true;
 
     vms->irqmap = a15irqmap;
 

include/hw/arm/virt.h

@@ -152,7 +152,7 @@ struct VirtMachineState {
     bool virt;
     bool ras;
     bool mte;
-    bool dtb_kaslr_seed;
+    bool dtb_randomness;
     OnOffAuto acpi;
     VirtGICType gic_version;
     VirtIOMMUType iommu;