diff options
Diffstat (limited to 'src/corelib/global/qrandom.cpp')
| -rw-r--r-- | src/corelib/global/qrandom.cpp | 96 |
1 files changed, 58 insertions, 38 deletions
diff --git a/src/corelib/global/qrandom.cpp b/src/corelib/global/qrandom.cpp index 66f21bc7f0..0fa67f69f8 100644 --- a/src/corelib/global/qrandom.cpp +++ b/src/corelib/global/qrandom.cpp @@ -46,6 +46,8 @@ #include <qthreadstorage.h> #include <private/qsimd_p.h> +#include <errno.h> + #if QT_CONFIG(cxx11_random) # include <random> # include "qdeadlinetimer.h" @@ -223,58 +225,76 @@ static void fallback_update_seed(unsigned value) seed.fetchAndXorRelaxed(value); } -static void emergency_seed(quint32 &v) Q_DECL_NOTHROW -{ - // we don't have any seed at all, so let's use the some bits from the - // seed variable's address (hoping to get entropy from the system ASLR) - // and the current monotonic time in nanoseconds - // (wall-clock time can be predicted) - - v = quint32(quintptr(&seed)) >> 12; // PAGE_SHIFT - if (sizeof(quintptr) == sizeof(quint32)) { - // mask off highest 4 bits, since they're likely to be constant - v &= ~0xf00000000U; - } - -#ifndef QT_BUILD_QMAKE - // see QtPrivate::QHashCombine for the algorithm - quint32 nsecs = quint32(QDeadlineTimer::current(Qt::PreciseTimer).deadline()); - v = QtPrivate::QHashCombine()(v, nsecs); -#endif -} - Q_NEVER_INLINE #ifdef Q_CC_GNU __attribute__((cold)) // this function is pretty big, so optimize for size #endif static void fallback_fill(quint32 *ptr, qssize_t left) Q_DECL_NOTHROW { + quint32 scratch[12]; // see element count below + quint32 *end = scratch; + + auto foldPointer = [](quintptr v) { + if (sizeof(quintptr) == sizeof(quint32)) { + // For 32-bit systems, we simply return the pointer. + return quint32(v); + } else { + // For 64-bit systems, we try to return the variable part of the + // pointer. On current x86-64 and AArch64, the top 17 bits are + // architecturally required to be the same, but in reality the top + // 24 bits on Linux are likely to be the same for all processes. + return quint32(v >> (32 - 24)); + } + }; + Q_ASSERT(left); - // ELF's auxv AT_RANDOM has 16 random bytes - using RandomBytes = quint32[16 / sizeof(quint32)]; - RandomBytes scratch = {}; - RandomBytes *auxvSeed = nullptr; + *end++ = foldPointer(quintptr(&seed)); // 1: variable in this library/executable's .data + *end++ = foldPointer(quintptr(&scratch)); // 2: variable in the stack + *end++ = foldPointer(quintptr(&errno)); // 3: veriable either in libc or thread-specific + *end++ = foldPointer(quintptr(reinterpret_cast<void*>(strerror))); // 4: function in libc (and unlikely to be a macro) -#if QT_HAS_INCLUDE(<sys/auxv.h>) && defined(AT_RANDOM) - // works on Linux -- all modern libc have getauxval - // other ELF-based systems don't seem to have AT_RANDOM - auxvSeed = reinterpret_cast<RandomBytes *>(getauxval(AT_RANDOM)); - if (auxvSeed) - memcpy(scratch, auxvSeed, sizeof(RandomBytes)); +#ifndef QT_BOOTSTRAPPED + quint64 nsecs = QDeadlineTimer::current(Qt::PreciseTimer).deadline(); + *end++ = quint32(nsecs); // 5 #endif - quint32 v = seed.load(); - if (Q_LIKELY(v)) { - // mix the stored seed value - // (using the fact that qHash(unsigned) is idempotent) - scratch[0] = QtPrivate::QHashCombine()(scratch[0], v); - } else if (Q_UNLIKELY(auxvSeed == nullptr)) { - emergency_seed(scratch[0]); + if (quint32 v = seed.load()) + *end++ = v; // 6 + +#if QT_CONFIG(sys_auxv) + // works on Linux -- all modern libc have getauxval +# ifdef AT_RANDOM + // ELF's auxv AT_RANDOM has 16 random bytes + // (other ELF-based systems don't seem to have AT_RANDOM) + ulong auxvSeed = getauxval(AT_RANDOM); + if (auxvSeed) { + memcpy(scratch, reinterpret_cast<void *>(auxvSeed), 16); + end += 4; // 7 to 10 } +# endif + + // Both AT_BASE and AT_SYSINFO_EHDR have some randomness in them due to the + // system's ASLR, even if many bits are the same. They also have randomness + // between them. +# ifdef AT_BASE + // present at least on the BSDs too, indicates the address of the loader + ulong base = getauxval(AT_BASE); + if (base) + *end++ = foldPointer(base); // 11 +# endif +# ifdef AT_SYSINFO_EHDR + // seems to be Linux-only, indicates the global page of the sysinfo + ulong sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR); + if (sysinfo_ehdr) + *end++ = foldPointer(sysinfo_ehdr); // 12 +# endif +#endif + + Q_ASSERT(end <= std::end(scratch)); // this is highly inefficient, we should save the generator across calls... - std::seed_seq sseq(std::begin(scratch), std::end(scratch)); + std::seed_seq sseq(scratch, end); std::mt19937 generator(sseq); std::generate(ptr, ptr + left, generator); |