arm64: kexec_file: add rng-seed support

Adding "rng-seed" to dtb. It's fine to add this property if original
fdt doesn't contain it. Since original seed will be wiped after
read, so use a default size 128 bytes here.
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/machine_kexec_file.c

@@ -27,6 +27,8 @@
 #define FDT_PROP_INITRD_END	"linux,initrd-end"
 #define FDT_PROP_BOOTARGS	"bootargs"
 #define FDT_PROP_KASLR_SEED	"kaslr-seed"
+#define FDT_PROP_RNG_SEED	"rng-seed"
+#define RNG_SEED_SIZE		128
 
 const struct kexec_file_ops * const kexec_file_loaders[] = {
 	&kexec_image_ops,
@@ -102,6 +104,19 @@ static int setup_dtb(struct kimage *image,
 				FDT_PROP_KASLR_SEED);
 	}
 
+	/* add rng-seed */
+	if (rng_is_initialized()) {
+		u8 rng_seed[RNG_SEED_SIZE];
+		get_random_bytes(rng_seed, RNG_SEED_SIZE);
+		ret = fdt_setprop(dtb, off, FDT_PROP_RNG_SEED, rng_seed,
+				RNG_SEED_SIZE);
+		if (ret)
+			goto out;
+	} else {
+		pr_notice("RNG is not initialised: omitting \"%s\" property\n",
+				FDT_PROP_RNG_SEED);
+	}
+
 out:
 	if (ret)
 		return (ret == -FDT_ERR_NOSPACE) ? -ENOMEM : -EINVAL;
@@ -110,7 +125,8 @@ static int setup_dtb(struct kimage *image,
 }
 
 /*
- * More space needed so that we can add initrd, bootargs and kaslr-seed.
+ * More space needed so that we can add initrd, bootargs, kaslr-seed, and
+ * rng-seed.
  */
 #define DTB_EXTRA_SPACE 0x1000