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[PATCH v2] mips/malta: pass RNG seed to to kernel via env var


From: Jason A. Donenfeld
Subject: [PATCH v2] mips/malta: pass RNG seed to to kernel via env var
Date: Mon, 3 Oct 2022 12:36:27 +0200

As of the kernel commit linked below, Linux ingests an 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.

Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Link: https://git.kernel.org/mips/c/056a68cea01
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
Changes v1->v2:
- Update commit message.
- No code changes.

 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




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