[v1] hw/arm/virt: Add DT property /secure-chosen/kaslr-seed

[PATCH] hw/arm/virt: Add DT property /secure-chosen/kaslr-seed

Posted by Jerome Forissier 4 years, 1 month ago

This commit generates a random seed to be used by the secure OS for
ASLR when the machine is secure. The seed is a 64-bit random value
exported via the DT in /secure-chosen/kaslr-seed. This interface is
used by OP-TEE [1].

[1] https://github.com/OP-TEE/optee_os/commit/ef262691fe0e

Signed-off-by: Jerome Forissier <jerome@forissier.org>
---
 hw/arm/virt.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 7dc96abf72c..42a6f84086f 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -77,6 +77,7 @@
 #include "hw/acpi/generic_event_device.h"
 #include "hw/virtio/virtio-iommu.h"
 #include "hw/char/pl011.h"
+#include "crypto/random.h"
 
 #define DEFINE_VIRT_MACHINE_LATEST(major, minor, latest) \
     static void virt_##major##_##minor##_class_init(ObjectClass *oc, \
@@ -1635,6 +1636,18 @@ static void finalize_gic_version(VirtMachineState *vms)
     }
 }
 
+static void create_secure_kaslr_seed(VirtMachineState *vms)
+{
+    Error *err = NULL;
+    uint64_t seed;
+
+    if (qcrypto_random_bytes(&seed, sizeof(seed), &err)) {
+        error_free(err);
+        return;
+    }
+    qemu_fdt_setprop_u64(vms->fdt, "/secure-chosen", "kaslr-seed", seed);
+}
+
 static void machvirt_init(MachineState *machine)
 {
     VirtMachineState *vms = VIRT_MACHINE(machine);
@@ -1837,6 +1850,7 @@ static void machvirt_init(MachineState *machine)
     if (vms->secure) {
         create_secure_ram(vms, secure_sysmem);
         create_uart(vms, VIRT_SECURE_UART, secure_sysmem, serial_hd(1));
+        create_secure_kaslr_seed(vms);
     }
 
     vms->highmem_ecam &= vms->highmem && (!firmware_loaded || aarch64);
-- 
2.20.1

Re: [PATCH] hw/arm/virt: Add DT property /secure-chosen/kaslr-seed

Posted by Peter Maydell 4 years, 1 month ago

On Fri, 10 Apr 2020 at 18:02, Jerome Forissier <jerome@forissier.org> wrote:
>
> This commit generates a random seed to be used by the secure OS for
> ASLR when the machine is secure. The seed is a 64-bit random value
> exported via the DT in /secure-chosen/kaslr-seed. This interface is
> used by OP-TEE [1].
>
> [1] https://github.com/OP-TEE/optee_os/commit/ef262691fe0e

The kernel devicetree documentation documents this as a generic
property of /chosen -- should we be providing a /chosen/kaslr-seed
too ?

> Signed-off-by: Jerome Forissier <jerome@forissier.org>
> ---

> +static void create_secure_kaslr_seed(VirtMachineState *vms)
> +{
> +    Error *err = NULL;
> +    uint64_t seed;
> +
> +    if (qcrypto_random_bytes(&seed, sizeof(seed), &err)) {
> +        error_free(err);
> +        return;
> +    }

Since this is exposed to the guest I'm wondering if we should
use qemu_guest_getrandom() (which lets you make the randomness
deterministic for the benefit of record-and-replay). But I'm
not sure if that function is usable before the guest has even
started running. Pavel, could you answer that?

> +    qemu_fdt_setprop_u64(vms->fdt, "/secure-chosen", "kaslr-seed", seed);
> +}
> +
>  static void machvirt_init(MachineState *machine)
>  {
>      VirtMachineState *vms = VIRT_MACHINE(machine);
> @@ -1837,6 +1850,7 @@ static void machvirt_init(MachineState *machine)
>      if (vms->secure) {
>          create_secure_ram(vms, secure_sysmem);
>          create_uart(vms, VIRT_SECURE_UART, secure_sysmem, serial_hd(1));
> +        create_secure_kaslr_seed(vms);

This is implicitly relying on create_uart() having created
the "/secure-chosen" node. I think it would be better now
that we have multiple things we might want to put there if we
just pulled the "create /secure-chosen" code out to the
create_fdt() function so we do it at the same place we
create "/chosen". (You can do that as a simple patch of its own
that comes before this one in the patchseries.)

>      }
>
>      vms->highmem_ecam &= vms->highmem && (!firmware_loaded || aarch64);

thanks
-- PMM

Re: [PATCH] hw/arm/virt: Add DT property /secure-chosen/kaslr-seed

Posted by Pavel Dovgalyuk 4 years, 1 month ago

On 17.04.2020 13:18, Peter Maydell wrote:
> On Fri, 10 Apr 2020 at 18:02, Jerome Forissier <jerome@forissier.org> wrote:
>> This commit generates a random seed to be used by the secure OS for
>> ASLR when the machine is secure. The seed is a 64-bit random value
>> exported via the DT in /secure-chosen/kaslr-seed. This interface is
>> used by OP-TEE [1].
>>
>> [1] https://github.com/OP-TEE/optee_os/commit/ef262691fe0e
> The kernel devicetree documentation documents this as a generic
> property of /chosen -- should we be providing a /chosen/kaslr-seed
> too ?
>
>> Signed-off-by: Jerome Forissier <jerome@forissier.org>
>> ---
>> +static void create_secure_kaslr_seed(VirtMachineState *vms)
>> +{
>> +    Error *err = NULL;
>> +    uint64_t seed;
>> +
>> +    if (qcrypto_random_bytes(&seed, sizeof(seed), &err)) {
>> +        error_free(err);
>> +        return;
>> +    }
> Since this is exposed to the guest I'm wondering if we should
> use qemu_guest_getrandom() (which lets you make the randomness
> deterministic for the benefit of record-and-replay). But I'm
> not sure if that function is usable before the guest has even
> started running. Pavel, could you answer that?

Yes, usage of deterministic functions is possible before machine is running,

because replay_configure is executed before machine initialization.


>
>> +    qemu_fdt_setprop_u64(vms->fdt, "/secure-chosen", "kaslr-seed", seed);
>> +}
>> +
>>   static void machvirt_init(MachineState *machine)
>>   {
>>       VirtMachineState *vms = VIRT_MACHINE(machine);
>> @@ -1837,6 +1850,7 @@ static void machvirt_init(MachineState *machine)
>>       if (vms->secure) {
>>           create_secure_ram(vms, secure_sysmem);
>>           create_uart(vms, VIRT_SECURE_UART, secure_sysmem, serial_hd(1));
>> +        create_secure_kaslr_seed(vms);
> This is implicitly relying on create_uart() having created
> the "/secure-chosen" node. I think it would be better now
> that we have multiple things we might want to put there if we
> just pulled the "create /secure-chosen" code out to the
> create_fdt() function so we do it at the same place we
> create "/chosen". (You can do that as a simple patch of its own
> that comes before this one in the patchseries.)
>
>>       }
>>
>>       vms->highmem_ecam &= vms->highmem && (!firmware_loaded || aarch64);
> thanks
> -- PMM

Re: [PATCH] hw/arm/virt: Add DT property /secure-chosen/kaslr-seed

Posted by Peter Maydell 4 years, 1 month ago

On Fri, 17 Apr 2020 at 13:01, Pavel Dovgalyuk <dovgaluk@ispras.ru> wrote:
>
>
> On 17.04.2020 13:18, Peter Maydell wrote:
> > On Fri, 10 Apr 2020 at 18:02, Jerome Forissier <jerome@forissier.org> wrote:
> >> This commit generates a random seed to be used by the secure OS for
> >> ASLR when the machine is secure. The seed is a 64-bit random value
> >> exported via the DT in /secure-chosen/kaslr-seed. This interface is
> >> used by OP-TEE [1].
> >>
> >> [1] https://github.com/OP-TEE/optee_os/commit/ef262691fe0e
> > The kernel devicetree documentation documents this as a generic
> > property of /chosen -- should we be providing a /chosen/kaslr-seed
> > too ?
> >
> >> Signed-off-by: Jerome Forissier <jerome@forissier.org>
> >> ---
> >> +static void create_secure_kaslr_seed(VirtMachineState *vms)
> >> +{
> >> +    Error *err = NULL;
> >> +    uint64_t seed;
> >> +
> >> +    if (qcrypto_random_bytes(&seed, sizeof(seed), &err)) {
> >> +        error_free(err);
> >> +        return;
> >> +    }
> > Since this is exposed to the guest I'm wondering if we should
> > use qemu_guest_getrandom() (which lets you make the randomness
> > deterministic for the benefit of record-and-replay). But I'm
> > not sure if that function is usable before the guest has even
> > started running. Pavel, could you answer that?
>
> Yes, usage of deterministic functions is possible before machine is running,
>
> because replay_configure is executed before machine initialization.

Great, thanks. Sonuds like we should use qemu_guest_getrandom() then.

-- PMM