Add support for the rdrand instruction, added in Intel's Ivy Bridge

processors. Tested using SDE on Linux with GCC 4.6, Intel C++ 11.1,
and Clang 3.0, all using the inline asm variant. I do not know if
current Visual C++ has the intrinsics available or not, so it's only
marked as available for those compilers at the moment.

4 files changed, 111 insertions, 0 deletions

diff --git a/src/entropy/rdrand/info.txt b/src/entropy/rdrand/info.txt
new file mode 100644
index 000000000..4b9362d61
--- /dev/null
+++ b/src/entropy/rdrand/info.txt
@@ -0,0 +1,20 @@
+define ENTROPY_SRC_RDRAND
+
+<source>
+rdrand.cpp
+</source>
+
+<header:internal>
+rdrand.h
+</header:internal>
+
+<arch>
+x86
+x86_64
+</arch>
+
+<cc>
+gcc
+clang
+icc
+</cc>
diff --git a/src/entropy/rdrand/rdrand.cpp b/src/entropy/rdrand/rdrand.cpp
new file mode 100644
index 000000000..72abd6166
--- /dev/null
+++ b/src/entropy/rdrand/rdrand.cpp
@@ -0,0 +1,55 @@
+/*
+* Entropy Source Using Intel's rdrand instruction
+* (C) 2012 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/internal/rdrand.h>
+#include <botan/cpuid.h>
+#include <immintrin.h>
+
+namespace Botan {
+
+/*
+* Get the timestamp
+*/
+void Intel_Rdrand::poll(Entropy_Accumulator& accum)
+   {
+   if(!CPUID::has_rdrand())
+      return;
+
+   /*
+   * Put an upper bound on the total entropy we're willing to claim
+   * for any one polling of rdrand to prevent it from swamping our
+   * poll. Internally, the rdrand system is a DRGB that reseeds at a
+   * somewhat unpredictable rate (the current conditions are
+   * documented, but that might not be true for different
+   * implementations, eg on Haswell or a future AMD chip, so I don't
+   * want to assume). This limit ensures we're going to poll at least
+   * one other source so we have some diversity in our inputs.
+   */
+
+   const size_t POLL_UPPER_BOUND = 96;
+   const size_t RDRAND_POLLS = 32;
+   const double ENTROPY_PER_POLL =
+      static_cast<double>(POLL_UPPER_BOUND) / (RDRAND_POLLS * 4);
+
+   for(size_t i = 0; i != RDRAND_POLLS; ++i)
+      {
+      unsigned int r;
+
+#if BOTAN_USE_GCC_INLINE_ASM
+      int cf = 0;
+      asm("rdrand %0; adcl $0,%1" :
+          "=r" (r), "=r" (cf) : "0" (r), "1" (cf) : "cc");
+#else
+      int cf = _rdrand32_step(&r);
+#endif
+
+      if(cf == 1)
+         accum.add(r, ENTROPY_PER_POLL);
+      }
+   }
+
+}
diff --git a/src/entropy/rdrand/rdrand.h b/src/entropy/rdrand/rdrand.h
new file mode 100644
index 000000000..d7629d37f
--- /dev/null
+++ b/src/entropy/rdrand/rdrand.h
@@ -0,0 +1,28 @@
+/*
+* Entropy Source Using Intel's rdrand instruction
+* (C) 2012 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#ifndef BOTAN_ENTROPY_SRC_RDRAND_H__
+#define BOTAN_ENTROPY_SRC_RDRAND_H__
+
+#include <botan/entropy_src.h>
+
+namespace Botan {
+
+/**
+* Entropy source using the rdrand instruction first introduced on
+* Intel's Ivy Bridge architecture.
+*/
+class Intel_Rdrand : public EntropySource
+   {
+   public:
+      std::string name() const { return "Intel Rdrand"; }
+      void poll(Entropy_Accumulator& accum);
+   };
+
+}
+
+#endif
diff --git a/src/libstate/global_rng.cpp b/src/libstate/global_rng.cpp
index e9ea530ac..7e7976f58 100644
--- a/src/libstate/global_rng.cpp
+++ b/src/libstate/global_rng.cpp
@@ -24,6 +24,10 @@
   #include <botan/internal/hres_timer.h>
 #endif
 
+#if defined(BOTAN_HAS_ENTROPY_SRC_RDRAND)
+  #include <botan/internal/rdrand.h>
+#endif
+
 #if defined(BOTAN_HAS_ENTROPY_SRC_DEV_RANDOM)
   #include <botan/internal/dev_random.h>
 #endif
@@ -65,6 +69,10 @@ void add_entropy_sources(RandomNumberGenerator* rng)
    rng->add_entropy_source(new High_Resolution_Timestamp);
 #endif
 
+#if defined(BOTAN_HAS_ENTROPY_SRC_RDRAND)
+   rng->add_entropy_source(new Intel_Rdrand);
+#endif
+
 #if defined(BOTAN_HAS_ENTROPY_SRC_DEV_RANDOM)
    rng->add_entropy_source(
       new Device_EntropySource(