[PATCH] hw/riscv: virt: pass random seed to fdt

["Jason A. Donenfeld" <Jason@zx2c4.com>]

If the FDT contains /chosen/rng-seed, then the Linux RNG will use it to
initialize early. Set this using the usual guest random number
generation function. This is confirmed to successfully initialize the
RNG on Linux 5.19-rc2.

Cc: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 hw/riscv/virt.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index bc424dd2f5..368a723bf6 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -21,6 +21,7 @@
 #include "qemu/osdep.h"
 #include "qemu/units.h"
 #include "qemu/error-report.h"
+#include "qemu/guest-random.h"
 #include "qapi/error.h"
 #include "hw/boards.h"
 #include "hw/loader.h"
@@ -998,6 +999,7 @@ static void create_fdt(RISCVVirtState *s, const MemMapEntry *memmap,
     MachineState *mc = MACHINE(s);
     uint32_t phandle = 1, irq_mmio_phandle = 1, msi_pcie_phandle = 1;
     uint32_t irq_pcie_phandle = 1, irq_virtio_phandle = 1;
+    uint8_t rng_seed[32];
 
     if (mc->dtb) {
         mc->fdt = load_device_tree(mc->dtb, &s->fdt_size);
@@ -1046,6 +1048,10 @@ update_bootargs:
     if (cmdline && *cmdline) {
         qemu_fdt_setprop_string(mc->fdt, "/chosen", "bootargs", cmdline);
     }
+
+    /* Pass seed to RNG. */
+    qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
+    qemu_fdt_setprop(mc->fdt, "/chosen", "rng-seed", rng_seed, sizeof(rng_seed));
 }
 
 static inline DeviceState *gpex_pcie_init(MemoryRegion *sys_mem,
-- 
2.35.1