[GWP-ASan] Move random-related code in the allocator (redo)

[cryptoad]

Summary

This is a redo of D89908, which triggered some -Werror=conversion
errors with GCC due to assignments to the 31-bit variable.

This CL adds to the original one a 31-bit mask variable that is used
at every assignment to silence the warning.

[nikic]

I can confirm that this builds fine for me.

[cryptoad]

In D89984#2348398, @nikic wrote:

I can confirm that this builds fine for me.

Thank you Nikita!

compiler-rt/lib/gwp_asan/CMakeLists.txt

 add_compiler_rt_component(gwp_asan)
 
 include_directories(..)
 
 set(GWP_ASAN_SOURCES
   common.cpp
   crash_handler.cpp
   platform_specific/common_posix.cpp
   platform_specific/guarded_pool_allocator_posix.cpp
   platform_specific/mutex_posix.cpp
   platform_specific/utilities_posix.cpp
   guarded_pool_allocator.cpp
-  random.cpp
   stack_trace_compressor.cpp
   utilities.cpp
 )
 
 set(GWP_ASAN_HEADERS
   common.h
   crash_handler.h
   definitions.h
   guarded_pool_allocator.h
   mutex.h
   options.h
   options.inc
-  random.h
   stack_trace_compressor.h
   utilities.h
 )
 
 # Ensure that GWP-ASan meets the delegated requirements of some supporting
 # allocators. Some supporting allocators (e.g. scudo standalone) cannot use any
 # parts of the C++ standard library.
 set(GWP_ASAN_CFLAGS ${SANITIZER_COMMON_CFLAGS} -fno-rtti -fno-exceptions

compiler-rt/lib/gwp_asan/guarded_pool_allocator.h

 //===-- guarded_pool_allocator.h --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef GWP_ASAN_GUARDED_POOL_ALLOCATOR_H_
 #define GWP_ASAN_GUARDED_POOL_ALLOCATOR_H_
 
 #include "gwp_asan/common.h"
 #include "gwp_asan/definitions.h"
 #include "gwp_asan/mutex.h"
 #include "gwp_asan/options.h"
-#include "gwp_asan/random.h"
 #include "gwp_asan/stack_trace_compressor.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 namespace gwp_asan {
 // This class is the primary implementation of the allocator portion of GWP-
 // ASan. It is the sole owner of the pool of sequentially allocated guarded
GWP_ASAN_ALWAYS_INLINE bool shouldSample() {
     // NextSampleCounter == 0 means we "should regenerate the counter".
     //                   == 1 means we "should sample this allocation".
     // AdjustedSampleRatePlusOne is designed to intentionally underflow. This
     // class must be valid when zero-initialised, and we wish to sample as
     // infrequently as possible when this is the case, hence we underflow to
     // UINT32_MAX.
     if (GWP_ASAN_UNLIKELY(ThreadLocals.NextSampleCounter == 0))
       ThreadLocals.NextSampleCounter =
-          (getRandomUnsigned32() % (AdjustedSampleRatePlusOne - 1)) + 1;
+          ((getRandomUnsigned32() % (AdjustedSampleRatePlusOne - 1)) + 1) &
+          ThreadLocalPackedVariables::NextSampleCounterMask;
 
     return GWP_ASAN_UNLIKELY(--ThreadLocals.NextSampleCounter == 0);
   }
 
   // Returns whether the provided pointer is a current sampled allocation that
   // is owned by this pool.
   GWP_ASAN_ALWAYS_INLINE bool pointerIsMine(const void *Ptr) const {
     return State.pointerIsMine(Ptr);
private:
   // GWP-ASan is disabled, we wish to never spend wasted cycles recalculating
   // the sample rate.
   uint32_t AdjustedSampleRatePlusOne = 0;
 
   // Pack the thread local variables into a struct to ensure that they're in
   // the same cache line for performance reasons. These are the most touched
   // variables in GWP-ASan.
   struct alignas(8) ThreadLocalPackedVariables {
-    constexpr ThreadLocalPackedVariables() {}
+    constexpr ThreadLocalPackedVariables()
+        : RandomState(0xff82eb50), NextSampleCounter(0), RecursiveGuard(false) {
+    }
+    // Initialised to a magic constant so that an uninitialised GWP-ASan won't
+    // regenerate its sample counter for as long as possible. The xorshift32()
+    // algorithm used below results in getRandomUnsigned32(0xff82eb50) ==
+    // 0xfffffea4.
+    uint32_t RandomState;
     // Thread-local decrementing counter that indicates that a given allocation
     // should be sampled when it reaches zero.
-    uint32_t NextSampleCounter = 0;
+    uint32_t NextSampleCounter : 31;
+    // The mask is needed to silence conversion errors.
+    static const uint32_t NextSampleCounterMask = (1U << 31) - 1;
     // Guard against recursivity. Unwinders often contain complex behaviour that
     // may not be safe for the allocator (i.e. the unwinder calls dlopen(),
     // which calls malloc()). When recursive behaviour is detected, we will
     // automatically fall back to the supporting allocator to supply the
     // allocation.
-    bool RecursiveGuard = false;
+    bool RecursiveGuard : 1;
+  };
+  static_assert(sizeof(ThreadLocalPackedVariables) == sizeof(uint64_t),
+                "thread local data does not fit in a uint64_t");
+
+  class ScopedRecursiveGuard {
+  public:
+    ScopedRecursiveGuard() { ThreadLocals.RecursiveGuard = true; }
+    ~ScopedRecursiveGuard() { ThreadLocals.RecursiveGuard = false; }
   };
+
+  // Initialise the PRNG, platform-specific.
+  void initPRNG();
+
+  // xorshift (32-bit output), extremely fast PRNG that uses arithmetic
+  // operations only. Seeded using platform-specific mechanisms by initPRNG().
+  uint32_t getRandomUnsigned32();
+
   static GWP_ASAN_TLS_INITIAL_EXEC ThreadLocalPackedVariables ThreadLocals;
 };
 } // namespace gwp_asan
 
 #endif // GWP_ASAN_GUARDED_POOL_ALLOCATOR_H_

compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp

 //===-- guarded_pool_allocator.cpp ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "gwp_asan/guarded_pool_allocator.h"
 
 #include "gwp_asan/optional/segv_handler.h"
 #include "gwp_asan/options.h"
-#include "gwp_asan/random.h"
 #include "gwp_asan/utilities.h"
 
 // RHEL creates the PRIu64 format macro (for printing uint64_t's) only when this
 // macro is defined before including <inttypes.h>.
 #ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS 1
 #endif
 

 namespace gwp_asan {
 namespace {
 // Forward declare the pointer to the singleton version of this class.
 // Instantiated during initialisation, this allows the signal handler
 // to find this class in order to deduce the root cause of failures. Must not be
 // referenced by users outside this translation unit, in order to avoid
 // init-order-fiasco.
 GuardedPoolAllocator *SingletonPtr = nullptr;
-
-class ScopedBoolean {
-public:
-  ScopedBoolean(bool &B) : Bool(B) { Bool = true; }
-  ~ScopedBoolean() { Bool = false; }
-
-private:
-  bool &Bool;
-};
 } // anonymous namespace
 
 // Gets the singleton implementation of this class. Thread-compatible until
 // init() is called, thread-safe afterwards.
 GuardedPoolAllocator *GuardedPoolAllocator::getSingleton() {
   return SingletonPtr;
 }
 
 void GuardedPoolAllocator::init(const options::Options &Opts) {
   // Note: We return from the constructor here if GWP-ASan is not available.
   // This will stop heap-allocation of class members, as well as mmap() of the
   // guarded slots.
   if (!Opts.Enabled || Opts.SampleRate == 0 ||
       Opts.MaxSimultaneousAllocations == 0)
     return;
 
   Check(Opts.SampleRate >= 0, "GWP-ASan Error: SampleRate is < 0.");
-  Check(Opts.SampleRate <= INT32_MAX, "GWP-ASan Error: SampleRate is > 2^31.");
+  Check(Opts.SampleRate < (1 << 30), "GWP-ASan Error: SampleRate is >= 2^30.");
   Check(Opts.MaxSimultaneousAllocations >= 0,
         "GWP-ASan Error: MaxSimultaneousAllocations is < 0.");
 
   SingletonPtr = this;
   Backtrace = Opts.Backtrace;
 
   State.MaxSimultaneousAllocations = Opts.MaxSimultaneousAllocations;
 
void GuardedPoolAllocator::init(const options::Options &Opts) {
   // SampleRate) chance of sampling.
   if (Opts.SampleRate != 1)
     AdjustedSampleRatePlusOne = static_cast<uint32_t>(Opts.SampleRate) * 2 + 1;
   else
     AdjustedSampleRatePlusOne = 2;
 
   initPRNG();
   ThreadLocals.NextSampleCounter =
-      (getRandomUnsigned32() % (AdjustedSampleRatePlusOne - 1)) + 1;
+      ((getRandomUnsigned32() % (AdjustedSampleRatePlusOne - 1)) + 1) &
+      ThreadLocalPackedVariables::NextSampleCounterMask;
 
   State.GuardedPagePool = reinterpret_cast<uintptr_t>(GuardedPoolMemory);
   State.GuardedPagePoolEnd =
       reinterpret_cast<uintptr_t>(GuardedPoolMemory) + PoolBytesRequired;
 
   if (Opts.InstallForkHandlers)
     installAtFork();
 }

 
 static uintptr_t getPageAddr(uintptr_t Ptr, uintptr_t PageSize) {
   return Ptr & ~(PageSize - 1);
 }
 
 void *GuardedPoolAllocator::allocate(size_t Size) {
   // GuardedPagePoolEnd == 0 when GWP-ASan is disabled. If we are disabled, fall
   // back to the supporting allocator.
-  if (State.GuardedPagePoolEnd == 0)
+  if (State.GuardedPagePoolEnd == 0) {
+    ThreadLocals.NextSampleCounter =
+        (AdjustedSampleRatePlusOne - 1) &
+        ThreadLocalPackedVariables::NextSampleCounterMask;
     return nullptr;
+  }
 
   // Protect against recursivity.
   if (ThreadLocals.RecursiveGuard)
     return nullptr;
-  ScopedBoolean SB(ThreadLocals.RecursiveGuard);
+  ScopedRecursiveGuard SRG;
 
   if (Size == 0 || Size > State.maximumAllocationSize())
     return nullptr;
 
   size_t Index;
   {
     ScopedLock L(PoolMutex);
     Index = reserveSlot();
// pool during the expensive markInaccessible() call.
     // Ensure that the deallocation is recorded before marking the page as
     // inaccessible. Otherwise, a racy use-after-free will have inconsistent
     // metadata.
     Meta->RecordDeallocation();
 
     // Ensure that the unwinder is not called if the recursive flag is set,
     // otherwise non-reentrant unwinders may deadlock.
     if (!ThreadLocals.RecursiveGuard) {
-      ScopedBoolean B(ThreadLocals.RecursiveGuard);
+      ScopedRecursiveGuard SRG;
       Meta->DeallocationTrace.RecordBacktrace(Backtrace);
     }
   }
 
   markInaccessible(reinterpret_cast<void *>(SlotStart),
                    State.maximumAllocationSize(), kGwpAsanGuardPageName);
 
   // And finally, lock again to release the slot back into the pool.
size_t GuardedPoolAllocator::reserveSlot() {
   return SlotIndex;
 }
 
 void GuardedPoolAllocator::freeSlot(size_t SlotIndex) {
   assert(FreeSlotsLength < State.MaxSimultaneousAllocations);
   FreeSlots[FreeSlotsLength++] = SlotIndex;
 }
 
+uint32_t GuardedPoolAllocator::getRandomUnsigned32() {
+  uint32_t RandomState = ThreadLocals.RandomState;
+  RandomState ^= RandomState << 13;
+  RandomState ^= RandomState >> 17;
+  RandomState ^= RandomState << 5;
+  ThreadLocals.RandomState = RandomState;
+  return RandomState;
+}
+
 GWP_ASAN_TLS_INITIAL_EXEC
 GuardedPoolAllocator::ThreadLocalPackedVariables
     GuardedPoolAllocator::ThreadLocals;
 } // namespace gwp_asan

compiler-rt/lib/gwp_asan/options.inc

 
 GWP_ASAN_OPTION(int, MaxSimultaneousAllocations, 16,
                 "Number of simultaneously-guarded allocations available in the "
                 "pool. Defaults to 16.")
 
 GWP_ASAN_OPTION(int, SampleRate, 5000,
                 "The probability (1 / SampleRate) that an allocation is "
                 "selected for GWP-ASan sampling. Default is 5000. Sample rates "
-                "up to (2^31 - 1) are supported.")
+                "up to (2^30 - 1) are supported.")
 
 // Developer note - This option is not actually processed by GWP-ASan itself. It
 // is included here so that a user can specify whether they want signal handlers
 // or not. The supporting allocator should inspect this value to see whether
 // signal handlers need to be installed, and then use
 // crash_handler::installSignalHandlers() in order to install the handlers. Note
 // that in order to support signal handlers, you will need to link against the
 // optional crash_handler component.

compiler-rt/lib/gwp_asan/platform_specific/guarded_pool_allocator_posix.cpp

 
 #include <assert.h>
 #include <errno.h>
 #include <signal.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
 #include <sys/types.h>
+#include <time.h>
 #include <unistd.h>
 
 #ifdef ANDROID
 #include <sys/prctl.h>
 #define PR_SET_VMA 0x53564d41
 #define PR_SET_VMA_ANON_NAME 0
 #endif // ANDROID
 
 void MaybeSetMappingName(void *Mapping, size_t Size, const char *Name) {
 #ifdef ANDROID
   prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, Mapping, Size, Name);
 #endif // ANDROID
   // Anonymous mapping names are only supported on Android.
   return;
 }
 
 namespace gwp_asan {
+
+void GuardedPoolAllocator::initPRNG() {
+  ThreadLocals.RandomState = time(nullptr) + getThreadID();
+}
+
 void *GuardedPoolAllocator::mapMemory(size_t Size, const char *Name) const {
   void *Ptr =
       mmap(nullptr, Size, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
   Check(Ptr != MAP_FAILED, "Failed to map guarded pool allocator memory");
   MaybeSetMappingName(Ptr, Size, Name);
   return Ptr;
 }
 

compiler-rt/lib/gwp_asan/random.h

-//===-- random.h ------------------------------------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef GWP_ASAN_RANDOM_H_
-#define GWP_ASAN_RANDOM_H_
-
-#include <stdint.h>
-
-namespace gwp_asan {
-// Initialise the PRNG, using time and thread ID as the seed.
-void initPRNG();
-
-// xorshift (32-bit output), extremely fast PRNG that uses arithmetic operations
-// only. Seeded using walltime.
-uint32_t getRandomUnsigned32();
-} // namespace gwp_asan
-
-#endif // GWP_ASAN_RANDOM_H_

compiler-rt/lib/gwp_asan/random.cpp

-//===-- random.cpp ----------------------------------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "gwp_asan/random.h"
-#include "gwp_asan/common.h"
-
-#include <time.h>
-
-// Initialised to a magic constant so that an uninitialised GWP-ASan won't
-// regenerate its sample counter for as long as possible. The xorshift32()
-// algorithm used below results in getRandomUnsigned32(0xff82eb50) ==
-// 0xfffffea4.
-GWP_ASAN_TLS_INITIAL_EXEC uint32_t RandomState = 0xff82eb50;
-
-namespace gwp_asan {
-void initPRNG() { RandomState = time(nullptr) + getThreadID(); }
-
-uint32_t getRandomUnsigned32() {
-  RandomState ^= RandomState << 13;
-  RandomState ^= RandomState >> 17;
-  RandomState ^= RandomState << 5;
-  return RandomState;
-}
-} // namespace gwp_asan