On 17.04.2020 13:18, Peter Maydell wrote:
On Fri, 10 Apr 2020 at 18:02, Jerome Forissier <jer...@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 <jer...@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
