On Wed, Jan 05, 2022 at 01:49:56PM +0000, Alex Bennée wrote:
> 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
>
>
Reviewed-by: Andrew Jones <drjo...@redhat.com>
