Merge #10377: Use rdrand as entropy source on supported platforms

cb24c85 Use rdrand as entropy source on supported platforms (Pieter Wuille)

Tree-SHA512: c42eaa01a14e6bc097c70b6bf8540d61854c2f76cb32be69c2a3c411a126f7b4bf4a4486e4493c4cc367cc689319abde0d4adb799d29a54fd3e81767ce0766fc

1 files changed, 68 insertions, 0 deletions

diff --git a/src/random.cpp b/src/random.cpp
index e1ccfa5f24..7916643263 100644
--- a/src/random.cpp
+++ b/src/random.cpp
@@ -65,6 +65,64 @@ static inline int64_t GetPerformanceCounter()
 #endif
 }
 
+
+#if defined(__x86_64__) || defined(__amd64__) || defined(__i386__)
+static std::atomic<bool> hwrand_initialized{false};
+static bool rdrand_supported = false;
+static constexpr uint32_t CPUID_F1_ECX_RDRAND = 0x40000000;
+static void RDRandInit()
+{
+    //! When calling cpuid function #1, ecx register will have this set if RDRAND is available.
+    // Avoid clobbering ebx, as that is used for PIC on x86.
+    uint32_t eax, tmp, ecx, edx;
+    __asm__ ("mov %%ebx, %1; cpuid; mov %1, %%ebx": "=a"(eax), "=g"(tmp), "=c"(ecx), "=d"(edx) : "a"(1));
+    if (ecx & CPUID_F1_ECX_RDRAND) {
+        LogPrintf("Using RdRand as entropy source\n");
+        rdrand_supported = true;
+    }
+    hwrand_initialized.store(true);
+}
+#else
+static void RDRandInit() {}
+#endif
+
+static bool GetHWRand(unsigned char* ent32) {
+#if defined(__x86_64__) || defined(__amd64__) || defined(__i386__)
+    assert(hwrand_initialized.load(std::memory_order_relaxed));
+    if (rdrand_supported) {
+        uint8_t ok;
+        // Not all assemblers support the rdrand instruction, write it in hex.
+#ifdef __i386__
+        for (int iter = 0; iter < 4; ++iter) {
+            uint32_t r1, r2;
+            __asm__ volatile (".byte 0x0f, 0xc7, 0xf0;" // rdrand %eax
+                              ".byte 0x0f, 0xc7, 0xf2;" // rdrand %edx
+                              "setc %2" :
+                              "=a"(r1), "=d"(r2), "=q"(ok) :: "cc");
+            if (!ok) return false;
+            WriteLE32(ent32 + 8 * iter, r1);
+            WriteLE32(ent32 + 8 * iter + 4, r2);
+        }
+#else
+        uint64_t r1, r2, r3, r4;
+        __asm__ volatile (".byte 0x48, 0x0f, 0xc7, 0xf0, " // rdrand %rax
+                                "0x48, 0x0f, 0xc7, 0xf3, " // rdrand %rbx
+                                "0x48, 0x0f, 0xc7, 0xf1, " // rdrand %rcx
+                                "0x48, 0x0f, 0xc7, 0xf2; " // rdrand %rdx
+                          "setc %4" :
+                          "=a"(r1), "=b"(r2), "=c"(r3), "=d"(r4), "=q"(ok) :: "cc");
+        if (!ok) return false;
+        WriteLE64(ent32, r1);
+        WriteLE64(ent32 + 8, r2);
+        WriteLE64(ent32 + 16, r3);
+        WriteLE64(ent32 + 24, r4);
+#endif
+        return true;
+    }
+#endif
+    return false;
+}
+
 void RandAddSeed()
 {
     // Seed with CPU performance counter
@@ -255,6 +313,11 @@ void GetStrongRandBytes(unsigned char* out, int num)
     GetOSRand(buf);
     hasher.Write(buf, 32);
 
+    // Third source: HW RNG, if available.
+    if (GetHWRand(buf)) {
+        hasher.Write(buf, 32);
+    }
+
     // Combine with and update state
     {
         std::unique_lock<std::mutex> lock(cs_rng_state);
@@ -381,3 +444,8 @@ FastRandomContext::FastRandomContext(bool fDeterministic) : requires_seed(!fDete
     uint256 seed;
     rng.SetKey(seed.begin(), 32);
 }
+
+void RandomInit()
+{
+    RDRandInit();
+}