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hw/arm: add control knob to disable kaslr_seed via DTB

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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.bennee@linaro.org>
Tested-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Acked-by: Jerome Forissier <jerome@forissier.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Message-Id: <20220105135009.1584676-22-alex.bennee@linaro.org>
This commit is contained in:
Alex Bennée 2022-01-05 13:49:56 +00:00
parent 7bef20d729
commit 33973e1e1f
3 changed files with 39 additions and 2 deletions
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8
docs/system/arm/virt.rst
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@ -121,6 +121,14 @@ 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-kaslr-seed
Set ``on``/``off`` to pass a random seed via the guest dtb
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
""""""""""""""""""""""""""""""""

32
hw/arm/virt.c
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@ -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->dtb_kaslr_seed) {
create_kaslr_seed(ms, "/chosen");
}
if (vms->secure) {
qemu_fdt_add_subnode(fdt, "/secure-chosen");
create_kaslr_seed(ms, "/secure-chosen");
if (vms->dtb_kaslr_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_dtb_kaslr_seed(Object *obj, Error **errp)
{
VirtMachineState *vms = VIRT_MACHINE(obj);
return vms->dtb_kaslr_seed;
}
static void virt_set_dtb_kaslr_seed(Object *obj, bool value, Error **errp)
{
VirtMachineState *vms = VIRT_MACHINE(obj);
vms->dtb_kaslr_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, "dtb-kaslr-seed",
virt_get_dtb_kaslr_seed,
virt_set_dtb_kaslr_seed);
object_class_property_set_description(oc, "dtb-kaslr-seed",
"Set off to disable passing of kaslr-seed "
"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->dtb_kaslr_seed = true;
vms->irqmap = a15irqmap;
virt_flash_create(vms);

1
include/hw/arm/virt.h
View File

@ -148,6 +148,7 @@ struct VirtMachineState {
bool virt;
bool ras;
bool mte;
bool dtb_kaslr_seed;
OnOffAuto acpi;
VirtGICType gic_version;
VirtIOMMUType iommu;