From 61ee28cb7da58d2aae96f9536e8bb869b13b7351 Mon Sep 17 00:00:00 2001
From: Emery Hemingway <ehmry@posteo.net>
Date: Sun, 31 Mar 2019 14:38:06 +0200
Subject: [PATCH] Use RDRAND to initialize blk_shred

Mix jitterentropy with RDRAND when initializing psuedo-random number
generator.
---
 src/app/blk_shred/main.cc | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/app/blk_shred/main.cc b/src/app/blk_shred/main.cc
index 2846884..b990218 100644
--- a/src/app/blk_shred/main.cc
+++ b/src/app/blk_shred/main.cc
@@ -26,6 +26,9 @@
 /* Jitterentropy includes */
 #include <jitterentropy.h>
 
+/* RDRAND utility */
+#include <world/rdrand.h>
+
 /* PCG includes */
 #include <pcg_variants.h>
 
@@ -80,7 +83,22 @@ struct Blk_shred::Main
 	void seed_noise()
 	{
 		/* read entropy into initialization variables */
-		jent_read_entropy(jent, (char*)&pcg_init, sizeof(pcg_init));
+
+		{
+			/* XOR in jitter entropy */
+			uint64_t buf[2] { 0 };
+			jent_read_entropy(jent, (char*)&buf, sizeof(buf));
+			pcg_init[0] ^= buf[0];
+			pcg_init[1] ^= buf[1];
+		}
+
+		if (Genode::Rdrand::supported()) {
+			/* XOR in RDRAND */
+			pcg_init[0] ^= Genode::Rdrand::random64();
+			pcg_init[1] ^= Genode::Rdrand::random64();
+		}
+
+		/* low bit must be set */
 		pcg_init[1] |= 1;
 
 		pcg32_srandom_r(&pcg, pcg_init[0], pcg_init[1]);