riscv: re-randomize rng-seed on reboot

When the system reboots, the rng-seed that the FDT has should be
re-randomized, so that the new boot gets a new seed. Since the FDT is in
the ROM region at this point, we add a hook right after the ROM has been
added, so that we have a pointer to that copy of the FDT.

Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Alistair Francis <alistair.francis@wdc.com>
Cc: Bin Meng <bin.meng@windriver.com>
Cc: qemu-riscv@nongnu.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20221025004327.568476-6-Jason@zx2c4.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/riscv/boot.c

@@ -30,6 +30,7 @@
 #include "sysemu/device_tree.h"
 #include "sysemu/qtest.h"
 #include "sysemu/kvm.h"
+#include "sysemu/reset.h"
 
 #include <libfdt.h>
 
@@ -241,6 +242,8 @@ uint64_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
 
     rom_add_blob_fixed_as("fdt", fdt, fdtsize, fdt_addr,
                           &address_space_memory);
+    qemu_register_reset_nosnapshotload(qemu_fdt_randomize_seeds,
+                        rom_ptr_for_as(&address_space_memory, fdt_addr, fdtsize));
 
     return fdt_addr;
 }