docs/system/arm/virt.rst | 17 ++++++++++------ hw/arm/virt.c | 44 ++++++++++++++++++++++++---------------- include/hw/arm/virt.h | 2 +- 3 files changed, 39 insertions(+), 24 deletions(-)
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>
---
docs/system/arm/virt.rst | 17 ++++++++++------
hw/arm/virt.c | 44 ++++++++++++++++++++++++----------------
include/hw/arm/virt.h | 2 +-
3 files changed, 39 insertions(+), 24 deletions(-)
diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index 3d1058a80c..3b6ba69a9a 100644
--- a/docs/system/arm/virt.rst
+++ b/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
- 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.
+ A deprecated synonym for dtb-randomness.
Linux guest kernel configuration
""""""""""""""""""""""""""""""""
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 097238faa7..924ded7f85 100644
--- a/hw/arm/virt.c
+++ b/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) {
- create_kaslr_seed(ms, "/chosen");
+ if (vms->dtb_randomness) {
+ create_randomness(ms, "/chosen");
}
if (vms->secure) {
qemu_fdt_add_subnode(fdt, "/secure-chosen");
- if (vms->dtb_kaslr_seed) {
- create_kaslr_seed(ms, "/secure-chosen");
+ if (vms->dtb_randomness) {
+ create_randomness(ms, "/secure-chosen");
}
}
@@ -2348,18 +2352,18 @@ 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)
@@ -2988,12 +2992,18 @@ 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_set_dtb_kaslr_seed);
+ virt_get_dtb_randomness,
+ virt_set_dtb_randomness);
object_class_property_set_description(oc, "dtb-kaslr-seed",
- "Set off to disable passing of kaslr-seed "
- "dtb node to guest");
+ "Deprecated synonym of dtb-randomness");
object_class_property_add_str(oc, "x-oem-id",
virt_get_oem_id,
@@ -3061,8 +3071,8 @@ 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;
+ /* Supply kaslr-seed and rng-seed by default */
+ vms->dtb_randomness = true;
vms->irqmap = a15irqmap;
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index 15feabac63..6ec479ca2b 100644
--- a/include/hw/arm/virt.h
+++ b/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;
--
2.35.1On Thu, 30 Jun 2022 at 11:39, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> 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>
Thanks for this respin; I think this is the right way to go.
> ---
> docs/system/arm/virt.rst | 17 ++++++++++------
> hw/arm/virt.c | 44 ++++++++++++++++++++++++----------------
> include/hw/arm/virt.h | 2 +-
> 3 files changed, 39 insertions(+), 24 deletions(-)
>
> diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
> index 3d1058a80c..3b6ba69a9a 100644
> --- a/docs/system/arm/virt.rst
> +++ b/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
> - 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.
> + A deprecated synonym for dtb-randomness.
We should also add a section to docs/about/deprecated.rst
noting that the old name is deprecated in favour of the new one.
I'll fold that in when I add the patch to target-arm.next, to
save you doing a respin:
--- a/docs/about/deprecated.rst
+++ b/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.
+
> + 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_set_dtb_kaslr_seed);
> + virt_get_dtb_randomness,
> + virt_set_dtb_randomness);
> object_class_property_set_description(oc, "dtb-kaslr-seed",
> - "Set off to disable passing of kaslr-seed "
> - "dtb node to guest");
> + "Deprecated synonym of dtb-randomness");
I was going to suggest object_property_add_alias() but that
works at the object level, not the class level, so never mind.
This will work, and eventually we'll delete the code when it
hits the deprecation-to-removal horizon. So
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
and applied to target-arm.next.
thanks
-- PMM
Hi Peter, On Mon, Jul 04, 2022 at 03:42:55PM +0100, Peter Maydell wrote: > We should also add a section to docs/about/deprecated.rst > noting that the old name is deprecated in favour of the new one. > I'll fold that in when I add the patch to target-arm.next, to > save you doing a respin: Thanks for doing that. Your text looks good to me. Jason
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