Add a replay allocator for ABA

Asan delays reallocation to increase the likelyhood of catching a UAF.  This adds a simple free list allocator
that tries to reuse allocations quickly to increase the chance of an ABA problem being detected.

.github/workflows/cmake.yml

@@ -34,6 +34,13 @@ jobs:
             cmake-flags: "-G Ninja -DSANITIZER=address,undefined -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang"
             dependencies: "sudo apt install ninja-build"
 
+          - variant: "Sanitizer with replay"
+            platform: "ubuntu-latest"
+            build-type: "Release"
+            cmake-flags: "-G Ninja -DUSE_REPLAY_ALLOCATOR=On -DSANITIZER=address,undefined -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang"
+            dependencies: "sudo apt install ninja-build"
+
+
           - platform: "windows-2019"
             build-type: "Debug"
             # Exclude perf tests in Debug on Windows as they take too long.

src/rt/CMakeLists.txt

@@ -37,6 +37,10 @@ if(USE_SYSTEMATIC_TESTING)
   target_compile_definitions(verona_rt INTERFACE USE_SYSTEMATIC_TESTING)
 endif()
 
+if(USE_REPLAY_ALLOCATOR)
+  target_compile_definitions(verona_rt INTERFACE USE_REPLAY_ALLOCATOR)
+endif()
+
 if(USE_CRASH_LOGGING)
   target_compile_definitions(verona_rt INTERFACE USE_FLIGHT_RECORDER)
 endif()

src/rt/debug/harness.h

@@ -146,6 +146,7 @@ class SystematicTestHarness
       Scheduler& sched = Scheduler::get();
 #ifdef USE_SYSTEMATIC_TESTING
       Systematic::set_seed(seed);
+      heap::set_seed(seed);
       if (seed % 2 == 1)
       {
         sched.set_fair(true);

src/rt/ds/heap.h

@@ -3,10 +3,177 @@
 
 #pragma once
 
+#include <array>
 #include <snmalloc/snmalloc.h>
 
+#if defined(__SANITIZE_ADDRESS__)
+#  define HAS_ASAN
+#elif defined(__has_feature)
+#  if __has_feature(address_sanitizer)
+#    define HAS_ASAN
+#  endif
+#endif
+
+#if defined(HAS_ASAN)
+#  include <sanitizer/asan_interface.h>
+// Asan does not appear to support a __asan_update_deallocation_context
+#  define VERONA_TRACK_FREE(ptr, size) __asan_poison_memory_region(ptr, size);
+#  define VERONA_TRACK_ALLOC(ptr, size) \
+    __asan_unpoison_memory_region(ptr, size); \
+    __asan_update_allocation_context(ptr);
+#  define VERONA_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address))
+#else
+#  define VERONA_TRACK_FREE(ptr, size)
+#  define VERONA_TRACK_ALLOC(ptr, size)
+#  define VERONA_NO_SANITIZE_ADDRESS
+#endif
+
 namespace verona::rt::heap
 {
+#ifdef USE_REPLAY_ALLOCATOR
+  class ReplayAllocator
+  {
+    struct Node
+    {
+      Node* next;
+    };
+
+    static inline std::array<Node*, 256> allocs;
+    static inline std::array<size_t, 256> lengths;
+    static inline snmalloc::FlagWord lock;
+    static inline PRNG rng;
+
+  public:
+    static void set_seed(uint64_t seed)
+    {
+      rng.set_seed(seed);
+    }
+
+    VERONA_NO_SANITIZE_ADDRESS
+    static void* alloc(size_t size)
+    {
+      auto sc = snmalloc::size_to_sizeclass_full(size);
+      auto idx = sc.index();
+      {
+        snmalloc::FlagLock l(lock);
+        if (lengths[idx] > 0)
+        {
+          // Reuse an element if there are at least 16, or
+          // the randomisation says to.
+          auto r = rng.next();
+          //          std::cout << std::hex <<  r << std::endl;
+
+          auto reuse = lengths[idx] > 16 || ((r & 0xf) == 0);
+          if (reuse)
+          {
+            auto r = rng.next();
+            Node** prev = &allocs[idx];
+            for (size_t i = 0; i < r % lengths[idx]; i++)
+            {
+              prev = &(*prev)->next;
+            }
+
+            auto curr = *prev;
+            auto next = curr->next;
+            *prev = next;
+            lengths[idx]--;
+            VERONA_TRACK_ALLOC(curr, size);
+            return curr;
+          }
+        }
+      }
+
+      return snmalloc::ThreadAlloc::get().alloc(size);
+    }
+
+    static void dealloc(void* ptr, size_t size)
+    {
+      auto sc = snmalloc::size_to_sizeclass_full(size);
+      auto idx = sc.index();
+      snmalloc::FlagLock l(lock);
+      auto hd = reinterpret_cast<Node*>(ptr);
+      hd->next = allocs[idx];
+      allocs[idx] = hd;
+      lengths[idx]++;
+      VERONA_TRACK_FREE(ptr, size);
+    }
+
+    VERONA_NO_SANITIZE_ADDRESS
+    static void flush()
+    {
+      for (size_t i = 0; i < allocs.size(); i++)
+      {
+        auto hd = allocs[i];
+        size_t count = 0;
+        while (hd != nullptr)
+        {
+          auto next = hd->next;
+          snmalloc::ThreadAlloc::get().dealloc(
+            hd, snmalloc::sizeclass_to_size(i));
+          hd = next;
+          count++;
+        }
+        assert(count == lengths[i]);
+        lengths[i] = 0;
+        allocs[i] = nullptr;
+      }
+    }
+  };
+
+  inline void* alloc(size_t size)
+  {
+    return ReplayAllocator::alloc(size);
+  }
+
+  template<size_t size>
+  inline void* alloc()
+  {
+    return ReplayAllocator::alloc(size);
+  }
+
+  inline void* calloc(size_t size)
+  {
+    auto obj = ReplayAllocator::alloc(size);
+    memset(obj, 0, size);
+    return obj;
+  }
+
+  template<size_t size>
+  inline void* calloc()
+  {
+    auto obj = ReplayAllocator::alloc(size);
+    memset(obj, 0, size);
+    return obj;
+  }
+
+  inline void dealloc(void* ptr, size_t size)
+  {
+    ReplayAllocator::dealloc(ptr, size);
+  }
+
+  inline void dealloc(void* ptr)
+  {
+    auto size = snmalloc::ThreadAlloc::get().alloc_size(ptr);
+    dealloc(ptr, size);
+  }
+
+  template<size_t size>
+  inline void dealloc(void* ptr)
+  {
+    ReplayAllocator::dealloc(ptr, size);
+  }
+
+  inline void debug_check_empty()
+  {
+    ReplayAllocator::flush();
+    snmalloc::debug_check_empty<snmalloc::Alloc::Config>();
+  }
+
+  inline void set_seed(uint64_t seed)
+  {
+    ReplayAllocator::set_seed(seed);
+  }
+#else
   inline void* alloc(size_t size)
   {
     return snmalloc::ThreadAlloc::get().alloc(size);
@@ -49,4 +216,10 @@ namespace verona::rt::heap
   {
     snmalloc::debug_check_empty<snmalloc::Alloc::Config>();
   }
+
+  inline void set_seed(uint64_t seed)
+  {
+    // Do nothing
+  }
+#endif
 } // namespace verona::rt::heap

test/func/replayalloc/replayalloc.cc

@@ -0,0 +1,63 @@
+// Copyright Microsoft and Project Verona Contributors.
+// SPDX-License-Identifier: MIT
+
+#define USE_REPLAY_ALLOCATOR
+
+#include <debug/harness.h>
+#include <test/opt.h>
+
+/**
+ * Tests heap replay functionality with systematic testing.
+ *
+ * We count each time alloc returns the value just freed, this should
+ * be possible, but not guaranteed.
+ **/
+
+size_t count = 0;
+
+void test_replay()
+{
+  size_t size = 16;
+  void* p = heap::alloc(size);
+  uintptr_t p_addr = (uintptr_t)p;
+  heap::dealloc(p, size);
+
+  void* p2 = heap::alloc(size);
+  uintptr_t p2_addr = (uintptr_t)p2;
+  heap::dealloc(p2, size);
+
+  if (p_addr == p2_addr)
+  {
+    std::cout << "*" << std::flush;
+    count++;
+  }
+  else
+  {
+    std::cout << "." << std::flush;
+  }
+}
+
+int main(int argc, char** argv)
+{
+  auto t = Aal::tick();
+  size_t repeats = 1000;
+  for (size_t i = 0; i < repeats; i++)
+  {
+    heap::set_seed(i + t);
+    test_replay();
+    heap::debug_check_empty();
+    if (i % 64 == 0)
+    {
+      std::cout << std::endl;
+    }
+  }
+
+  std::cout << std::endl << "count: " << count << std::endl;
+
+  // We should have at least one replay
+  check(count != 0);
+  // We should not have all replays
+  check(count != repeats);
+
+  return 0;
+}