[PATCH qemu] mips/malta: pass RNG seed to to kernel via env var

[Jason A. Donenfeld]

With the kernel patch linked below, Linux ingests a RNG seed
passed from the hypervisor. So, pass this for the Malta platform, and
reinitialize it on reboot too, so that it's always fresh.

Link: 
https://lore.kernel.org/linux-mips/20220930140138.575751-1-Jason@zx2c4.com/
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 hw/mips/malta.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/hw/mips/malta.c b/hw/mips/malta.c
index 0e932988e0..9d793b3c17 100644
--- a/hw/mips/malta.c
+++ b/hw/mips/malta.c
@@ -26,6 +26,7 @@
 #include "qemu/units.h"
 #include "qemu/bitops.h"
 #include "qemu/datadir.h"
+#include "qemu/guest-random.h"
 #include "hw/clock.h"
 #include "hw/southbridge/piix.h"
 #include "hw/isa/superio.h"
@@ -1017,6 +1018,17 @@ static void G_GNUC_PRINTF(3, 4) prom_set(uint32_t 
*prom_buf, int index,
     va_end(ap);
 }
 
+static void reinitialize_rng_seed(void *opaque)
+{
+    char *rng_seed_hex = opaque;
+    uint8_t rng_seed[32];
+
+    qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
+    for (size_t i = 0; i < sizeof(rng_seed); ++i) {
+        sprintf(rng_seed_hex + i * 2, "%02x", rng_seed[i]);
+    }
+}
+
 /* Kernel */
 static uint64_t load_kernel(void)
 {
@@ -1028,6 +1040,8 @@ static uint64_t load_kernel(void)
     long prom_size;
     int prom_index = 0;
     uint64_t (*xlate_to_kseg0) (void *opaque, uint64_t addr);
+    uint8_t rng_seed[32];
+    char rng_seed_hex[sizeof(rng_seed) * 2 + 1];
 
 #if TARGET_BIG_ENDIAN
     big_endian = 1;
@@ -1115,9 +1129,20 @@ static uint64_t load_kernel(void)
 
     prom_set(prom_buf, prom_index++, "modetty0");
     prom_set(prom_buf, prom_index++, "38400n8r");
+
+    qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
+    for (size_t i = 0; i < sizeof(rng_seed); ++i) {
+        sprintf(rng_seed_hex + i * 2, "%02x", rng_seed[i]);
+    }
+    prom_set(prom_buf, prom_index++, "rngseed");
+    prom_set(prom_buf, prom_index++, "%s", rng_seed_hex);
+
     prom_set(prom_buf, prom_index++, NULL);
 
     rom_add_blob_fixed("prom", prom_buf, prom_size, ENVP_PADDR);
+    qemu_register_reset(reinitialize_rng_seed,
+                        memmem(rom_ptr(ENVP_PADDR, prom_size), prom_size,
+                               rng_seed_hex, sizeof(rng_seed_hex)));
 
     g_free(prom_buf);
     return kernel_entry;
-- 
2.37.3