5 files changed, 72 insertions, 36 deletions

diff --git a/src/build-data/buildh.in b/src/build-data/buildh.in
index c6c4f9064..84756536d 100644
--- a/src/build-data/buildh.in
+++ b/src/build-data/buildh.in
@@ -173,6 +173,19 @@ softare-based entropy polling is still used.
 */
 #define BOTAN_ENTROPY_ESTIMATE_HARDWARE_RNG 0.0
 
+/*
+How often should the RdRand/RdSeed RNGs be polled
+
+Each poll generates 32 bit entropy
+*/
+#define BOTAN_ENTROPY_INTEL_RNG_POLLS 32
+
+/*
+* RdSeed is not guaranteed to generate a random number within a specific number of retries
+* Define the number of retries here
+*/
+#define BOTAN_ENTROPY_RDSEED_RETRIES 20
+
 // The output of a PRNG we are trusting to be strong
 #define BOTAN_ENTROPY_ESTIMATE_STRONG_RNG 7.0
 
diff --git a/src/lib/entropy/rdrand/rdrand.cpp b/src/lib/entropy/rdrand/rdrand.cpp
index 24fe98cf8..36eaebee3 100644
--- a/src/lib/entropy/rdrand/rdrand.cpp
+++ b/src/lib/entropy/rdrand/rdrand.cpp
@@ -7,39 +7,49 @@
 
 #include <botan/internal/rdrand.h>
 #include <botan/cpuid.h>
+#include <botan/exceptn.h>
+#include <botan/build.h>
 
 #if !defined(BOTAN_USE_GCC_INLINE_ASM)
   #include <immintrin.h>
 #endif
 
-namespace Botan {
-
-/*
-* Get the timestamp
-*/
-void Intel_Rdrand::poll(Entropy_Accumulator& accum)
-   {
-   if(!CPUID::has_rdrand())
-      return;
+// RDRAND is guaranteed to generate a random number within 10 retries on a working CPU
+#define INTEL_RDRAND_RETRIES 10
 
-   const size_t RDRAND_POLLS = 32;
+namespace Botan {
 
-   for(size_t i = 0; i != RDRAND_POLLS; ++i)
+uint32_t Intel_Rdrand::get32BitRandom() {
+   for ( size_t i = 0; i != INTEL_RDRAND_RETRIES; ++i )
       {
-      unsigned int r = 0;
+      uint32_t r = 0;
 
 #if defined(BOTAN_USE_GCC_INLINE_ASM)
       int cf = 0;
 
       // Encoding of rdrand %eax
-      asm(".byte 0x0F, 0xC7, 0xF0; adcl $0,%1" :
-          "=a" (r), "=r" (cf) : "0" (r), "1" (cf) : "cc");
+      asm( ".byte 0x0F, 0xC7, 0xF0; adcl $0,%1" :
+           "=a" ( r ), "=r" ( cf ) : "0" ( r ), "1" ( cf ) : "cc" );
 #else
-      int cf = _rdrand32_step(&r);
+      int cf = _rdrand32_step( &r );
 #endif
+      if ( 1 == cf )
+         {
+         return r;
+         }
+      }
+
+   throw Internal_Error( "RdRand failed after " + std::to_string( INTEL_RDRAND_RETRIES ) + " retries" );
+   }
 
-      if(cf == 1)
-         accum.add(r, BOTAN_ENTROPY_ESTIMATE_HARDWARE_RNG);
+void Intel_Rdrand::poll( Entropy_Accumulator& accum ) {
+   if ( !CPUID::has_rdrand() )
+      return;
+
+   for ( size_t i = 0; i != BOTAN_ENTROPY_INTEL_RNG_POLLS; ++i )
+      {
+      uint32_t random = get32BitRandom();
+      accum.add( random, BOTAN_ENTROPY_ESTIMATE_HARDWARE_RNG );
       }
    }
 
diff --git a/src/lib/entropy/rdrand/rdrand.h b/src/lib/entropy/rdrand/rdrand.h
index 1fa928641..5ace28382 100644
--- a/src/lib/entropy/rdrand/rdrand.h
+++ b/src/lib/entropy/rdrand/rdrand.h
@@ -20,7 +20,9 @@ class Intel_Rdrand : public Entropy_Source
    {
    public:
       std::string name() const override { return "rdrand"; }
-      void poll(Entropy_Accumulator& accum) override;
+      void poll( Entropy_Accumulator& accum ) override;
+   private:
+      static uint32_t get32BitRandom();
    };
 
 }
diff --git a/src/lib/entropy/rdseed/rdseed.cpp b/src/lib/entropy/rdseed/rdseed.cpp
index 91306769d..b995ab5d4 100644
--- a/src/lib/entropy/rdseed/rdseed.cpp
+++ b/src/lib/entropy/rdseed/rdseed.cpp
@@ -7,6 +7,7 @@
 
 #include <botan/internal/rdseed.h>
 #include <botan/cpuid.h>
+#include <botan/build.h>
 
 #if !defined(BOTAN_USE_GCC_INLINE_ASM)
   #include <immintrin.h>
@@ -14,32 +15,40 @@
 
 namespace Botan {
 
-/*
-* Get the timestamp
-*/
-void Intel_Rdseed::poll(Entropy_Accumulator& accum)
-   {
-   if(!CPUID::has_rdseed())
-      return;
-
-   const size_t RDSEED_POLLS = 32;
-
-   for(size_t i = 0; i != RDSEED_POLLS; ++i)
+/// @returns 0 if RdSeed failed after @param max_retries otherwise the 32 bit random number generated by RdSeed
+uint32_t Intel_Rdseed::get32BitRandom( const uint32_t max_retries ) {
+   for ( size_t i = 0; i != max_retries; ++i )
       {
-      unsigned int r = 0;
+      uint32_t r = 0;
 
 #if defined(BOTAN_USE_GCC_INLINE_ASM)
       int cf = 0;
 
       // Encoding of rdseed %eax
-      asm(".byte 0x0F, 0xC7, 0xF8; adcl $0,%1" :
-          "=a" (r), "=r" (cf) : "0" (r), "1" (cf) : "cc");
+      asm( ".byte 0x0F, 0xC7, 0xF8; adcl $0,%1" :
+           "=a" ( r ), "=r" ( cf ) : "0" ( r ), "1" ( cf ) : "cc" );
 #else
-      int cf = _rdseed32_step(&r);
+      int cf = _rdseed32_step( &r );
 #endif
+      if ( 1 == cf )
+         {
+         return r;
+         }
+      }
+   return 0;
+   }
 
-      if(cf == 1)
-         accum.add(r, BOTAN_ENTROPY_ESTIMATE_HARDWARE_RNG);
+void Intel_Rdseed::poll( Entropy_Accumulator& accum ) {
+   if ( !CPUID::has_rdseed() )
+      return;
+
+   for ( size_t i = 0; i != BOTAN_ENTROPY_INTEL_RNG_POLLS; ++i )
+      {
+      uint32_t random = get32BitRandom( BOTAN_ENTROPY_RDSEED_RETRIES );
+      if ( random )
+         {
+         accum.add( random, BOTAN_ENTROPY_ESTIMATE_HARDWARE_RNG );
+         }
       }
    }
 
diff --git a/src/lib/entropy/rdseed/rdseed.h b/src/lib/entropy/rdseed/rdseed.h
index 0f39250a1..a6f92709a 100644
--- a/src/lib/entropy/rdseed/rdseed.h
+++ b/src/lib/entropy/rdseed/rdseed.h
@@ -20,7 +20,9 @@ class Intel_Rdseed : public Entropy_Source
    {
    public:
       std::string name() const override { return "rdseed"; }
-      void poll(Entropy_Accumulator& accum) override;
+      void poll( Entropy_Accumulator& accum ) override;
+   private:
+      static uint32_t get32BitRandom( uint32_t max_retries );
    };
 
 }