Fix QRandomGenerator initialization on AMD CPUs

Some AMD CPUs (e.g. AMD A4-6250J and AMD Ryzen 3000-series) have a
failing random generation instruction, which always returns
0xffffffff, even when generation was "successful".

This code checks if hardware random generator generates four consecutive
equal numbers. If it does, then we probably have a failing one and
should disable it completely.

Change-Id: I38c87920ca2e8cce4143afbff5e453ce3845d11a
Fixes: QTBUG-69423
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

2 files changed, 2 insertions, 51 deletions

diff --git a/src/corelib/global/qrandom.cpp b/src/corelib/global/qrandom.cpp
index fa26d54afa..b150a29b88 100644
--- a/src/corelib/global/qrandom.cpp
+++ b/src/corelib/global/qrandom.cpp
@@ -90,47 +90,6 @@ DECLSPEC_IMPORT BOOLEAN WINAPI SystemFunction036(PVOID RandomBuffer, ULONG Rando
 
 QT_BEGIN_NAMESPACE
 
-#if defined(Q_PROCESSOR_X86) && QT_COMPILER_SUPPORTS_HERE(RDRND)
-static qsizetype qt_random_cpu(void *buffer, qsizetype count) Q_DECL_NOTHROW;
-
-#  ifdef Q_PROCESSOR_X86_64
-#    define _rdrandXX_step _rdrand64_step
-#  else
-#    define _rdrandXX_step _rdrand32_step
-#  endif
-
-static QT_FUNCTION_TARGET(RDRND) qsizetype qt_random_cpu(void *buffer, qsizetype count) Q_DECL_NOTHROW
-{
-    unsigned *ptr = reinterpret_cast<unsigned *>(buffer);
-    unsigned *end = ptr + count;
-    int retries = 10;
-
-    while (ptr + sizeof(qregisteruint)/sizeof(*ptr) <= end) {
-        if (_rdrandXX_step(reinterpret_cast<qregisteruint *>(ptr)))
-            ptr += sizeof(qregisteruint)/sizeof(*ptr);
-        else if (--retries == 0)
-            goto out;
-    }
-
-    while (sizeof(*ptr) != sizeof(qregisteruint) && ptr != end) {
-        bool ok = _rdrand32_step(ptr);
-        if (!ok && --retries)
-            continue;
-        if (ok)
-            ++ptr;
-        break;
-    }
-
-out:
-    return ptr - reinterpret_cast<unsigned *>(buffer);
-}
-#else
-static qsizetype qt_random_cpu(void *, qsizetype)
-{
-    return 0;
-}
-#endif
-
 enum {
     // may be "overridden" by a member enum
     FillBufferNoexcept = true
@@ -371,8 +330,8 @@ Q_NEVER_INLINE void QRandomGenerator::SystemGenerator::generate(quint32 *begin,
     }
 
     qsizetype filled = 0;
-    if (qt_has_hwrng() && (uint(qt_randomdevice_control) & SkipHWRNG) == 0)
-        filled += qt_random_cpu(buffer, count);
+    if (qHasHwrng() && (uint(qt_randomdevice_control) & SkipHWRNG) == 0)
+        filled += qRandomCpu(buffer, count);
 
     if (filled != count && (uint(qt_randomdevice_control) & SkipSystemRNG) == 0) {
         qsizetype bytesFilled =
diff --git a/src/corelib/global/qrandom_p.h b/src/corelib/global/qrandom_p.h
index 917a91098e..4a0adff51c 100644
--- a/src/corelib/global/qrandom_p.h
+++ b/src/corelib/global/qrandom_p.h
@@ -79,14 +79,6 @@ extern Q_CORE_EXPORT QBasicAtomicInteger<uint> qt_randomdevice_control;
 enum { qt_randomdevice_control = 0 };
 #endif
 
-inline bool qt_has_hwrng()
-{
-#if defined(Q_PROCESSOR_X86) && QT_COMPILER_SUPPORTS_HERE(RDRND)
-    return qCpuHasFeature(RDRND);
-#else
-    return false;
-#endif
-}
 
 
 QT_END_NAMESPACE