Generally a guest needs an external source of randomness to properly
enable things like address space randomisation. However in a trusted
boot environment where the firmware will cryptographically verify
components having random data in the DTB will cause verification to
fail. Add a control knob so we can prevent this being added to the
system DTB.
Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
Tested-by: Heinrich Schuchardt <xypron.g...@gmx.de>
Acked-by: Ilias Apalodimas <ilias.apalodi...@linaro.org>
Acked-by: Jerome Forissier <jer...@forissier.org>
Message-Id: <20211215120926.1696302-1-alex.ben...@linaro.org>
---
docs/system/arm/virt.rst | 7 +++++++
include/hw/arm/virt.h | 1 +
hw/arm/virt.c | 32 ++++++++++++++++++++++++++++++--
3 files changed, 38 insertions(+), 2 deletions(-)
diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index 850787495b..c86a4808df 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -121,6 +121,13 @@ 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.
+kaslr-dtb-seed
+ Set ``on``/``off`` to pass a random seed via the guest dtb 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
""""""""""""""""""""""""""""""""
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index dc6b66ffc8..acd0665fe7 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -148,6 +148,7 @@ struct VirtMachineState {
bool virt;
bool ras;
bool mte;
+ bool kaslr_dtb_seed;
OnOffAuto acpi;
VirtGICType gic_version;
VirtIOMMUType iommu;
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 6bce595aba..1781e47c76 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -247,11 +247,15 @@ static void create_fdt(VirtMachineState *vms)
/* /chosen must exist for load_dtb to fill in necessary properties later */
qemu_fdt_add_subnode(fdt, "/chosen");
- create_kaslr_seed(ms, "/chosen");
+ if (vms->kaslr_dtb_seed) {
+ create_kaslr_seed(ms, "/chosen");
+ }
if (vms->secure) {
qemu_fdt_add_subnode(fdt, "/secure-chosen");
- create_kaslr_seed(ms, "/secure-chosen");
+ if (vms->kaslr_dtb_seed) {
+ create_kaslr_seed(ms, "/secure-chosen");
+ }
}
/* Clock node, for the benefit of the UART. The kernel device tree
@@ -2235,6 +2239,20 @@ static void virt_set_its(Object *obj, bool value, Error
**errp)
vms->its = value;
}
+static bool virt_get_kaslr_dtb_seed(Object *obj, Error **errp)
+{
+ VirtMachineState *vms = VIRT_MACHINE(obj);
+
+ return vms->kaslr_dtb_seed;
+}
+
+static void virt_set_kaslr_dtb_seed(Object *obj, bool value, Error **errp)
+{
+ VirtMachineState *vms = VIRT_MACHINE(obj);
+
+ vms->kaslr_dtb_seed = value;
+}
+
static char *virt_get_oem_id(Object *obj, Error **errp)
{
VirtMachineState *vms = VIRT_MACHINE(obj);
@@ -2764,6 +2782,13 @@ static void virt_machine_class_init(ObjectClass *oc,
void *data)
"Set on/off to enable/disable "
"ITS instantiation");
+ object_class_property_add_bool(oc, "kaslr-dtb-seed",
+ virt_get_kaslr_dtb_seed,
+ virt_set_kaslr_dtb_seed);
+ object_class_property_set_description(oc, "kaslr-dtb-seed",
+ "Set off to disable passing of kaslr
"
+ "dtb node to guest");
+
object_class_property_add_str(oc, "x-oem-id",
virt_get_oem_id,
virt_set_oem_id);
@@ -2828,6 +2853,9 @@ static void virt_instance_init(Object *obj)
/* MTE is disabled by default. */
vms->mte = false;
+ /* Supply a kaslr-seed by default */
+ vms->kaslr_dtb_seed = true;
+
vms->irqmap = a15irqmap;
virt_flash_create(vms);
--
2.30.2
