1 files changed, 208 insertions, 0 deletions
diff --git a/mfbt/Poison.cpp b/mfbt/Poison.cpp
new file mode 100644
index 000000000..b2767011d
--- /dev/null
+++ b/mfbt/Poison.cpp
@@ -0,0 +1,208 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * A poison value that can be used to fill a memory space with
+ * an address that leads to a safe crash when dereferenced.
+ */
+
+#include "mozilla/Poison.h"
+
+#include "mozilla/Assertions.h"
+#ifdef _WIN32
+# include <windows.h>
+#elif !defined(__OS2__)
+# include <unistd.h>
+# include <sys/mman.h>
+# ifndef MAP_ANON
+#  ifdef MAP_ANONYMOUS
+#   define MAP_ANON MAP_ANONYMOUS
+#  else
+#   error "Don't know how to get anonymous memory"
+#  endif
+# endif
+#endif
+
+extern "C" {
+uintptr_t gMozillaPoisonValue;
+uintptr_t gMozillaPoisonBase;
+uintptr_t gMozillaPoisonSize;
+}
+
+// Freed memory is filled with a poison value, which we arrange to
+// form a pointer either to an always-unmapped region of the address
+// space, or to a page that has been reserved and rendered
+// inaccessible via OS primitives.  See tests/TestPoisonArea.cpp for
+// extensive discussion of the requirements for this page.  The code
+// from here to 'class FreeList' needs to be kept in sync with that
+// file.
+
+#ifdef _WIN32
+static void*
+ReserveRegion(uintptr_t aRegion, uintptr_t aSize)
+{
+  return VirtualAlloc((void*)aRegion, aSize, MEM_RESERVE, PAGE_NOACCESS);
+}
+
+static void
+ReleaseRegion(void* aRegion, uintptr_t aSize)
+{
+  VirtualFree(aRegion, aSize, MEM_RELEASE);
+}
+
+static bool
+ProbeRegion(uintptr_t aRegion, uintptr_t aSize)
+{
+  SYSTEM_INFO sinfo;
+  GetSystemInfo(&sinfo);
+  if (aRegion >= (uintptr_t)sinfo.lpMaximumApplicationAddress &&
+      aRegion + aSize >= (uintptr_t)sinfo.lpMaximumApplicationAddress) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
+static uintptr_t
+GetDesiredRegionSize()
+{
+  SYSTEM_INFO sinfo;
+  GetSystemInfo(&sinfo);
+  return sinfo.dwAllocationGranularity;
+}
+
+#define RESERVE_FAILED 0
+
+#elif defined(__OS2__)
+static void*
+ReserveRegion(uintptr_t aRegion, uintptr_t aSize)
+{
+  // OS/2 doesn't support allocation at an arbitrary address,
+  // so return an address that is known to be invalid.
+  return (void*)0xFFFD0000;
+}
+
+static void
+ReleaseRegion(void* aRegion, uintptr_t aSize)
+{
+  return;
+}
+
+static bool
+ProbeRegion(uintptr_t aRegion, uintptr_t aSize)
+{
+  // There's no reliable way to probe an address in the system
+  // arena other than by touching it and seeing if a trap occurs.
+  return false;
+}
+
+static uintptr_t
+GetDesiredRegionSize()
+{
+  // Page size is fixed at 4k.
+  return 0x1000;
+}
+
+#define RESERVE_FAILED 0
+
+#else // Unix
+
+#include "mozilla/TaggedAnonymousMemory.h"
+
+static void*
+ReserveRegion(uintptr_t aRegion, uintptr_t aSize)
+{
+  return MozTaggedAnonymousMmap(reinterpret_cast<void*>(aRegion), aSize,
+                                PROT_NONE, MAP_PRIVATE|MAP_ANON, -1, 0,
+                                "poison");
+}
+
+static void
+ReleaseRegion(void* aRegion, uintptr_t aSize)
+{
+  munmap(aRegion, aSize);
+}
+
+static bool
+ProbeRegion(uintptr_t aRegion, uintptr_t aSize)
+{
+  if (madvise(reinterpret_cast<void*>(aRegion), aSize, MADV_NORMAL)) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
+static uintptr_t
+GetDesiredRegionSize()
+{
+  return sysconf(_SC_PAGESIZE);
+}
+
+#define RESERVE_FAILED MAP_FAILED
+
+#endif // system dependencies
+
+static_assert(sizeof(uintptr_t) == 4 || sizeof(uintptr_t) == 8, "");
+static_assert(sizeof(uintptr_t) == sizeof(void*), "");
+
+static uintptr_t
+ReservePoisonArea(uintptr_t rgnsize)
+{
+  if (sizeof(uintptr_t) == 8) {
+    // Use the hardware-inaccessible region.
+    // We have to avoid 64-bit constants and shifts by 32 bits, since this
+    // code is compiled in 32-bit mode, although it is never executed there.
+    return
+      (((uintptr_t(0x7FFFFFFFu) << 31) << 1 | uintptr_t(0xF0DEAFFFu))
+       & ~(rgnsize-1));
+  }
+
+  // First see if we can allocate the preferred poison address from the OS.
+  uintptr_t candidate = (0xF0DEAFFF & ~(rgnsize-1));
+  void* result = ReserveRegion(candidate, rgnsize);
+  if (result == (void*)candidate) {
+    // success - inaccessible page allocated
+    return candidate;
+  }
+
+  // That didn't work, so see if the preferred address is within a range
+  // of permanently inacessible memory.
+  if (ProbeRegion(candidate, rgnsize)) {
+    // success - selected page cannot be usable memory
+    if (result != RESERVE_FAILED) {
+      ReleaseRegion(result, rgnsize);
+    }
+    return candidate;
+  }
+
+  // The preferred address is already in use.  Did the OS give us a
+  // consolation prize?
+  if (result != RESERVE_FAILED) {
+    return uintptr_t(result);
+  }
+
+  // It didn't, so try to allocate again, without any constraint on
+  // the address.
+  result = ReserveRegion(0, rgnsize);
+  if (result != RESERVE_FAILED) {
+    return uintptr_t(result);
+  }
+
+  MOZ_CRASH("no usable poison region identified");
+}
+
+void
+mozPoisonValueInit()
+{
+  gMozillaPoisonSize = GetDesiredRegionSize();
+  gMozillaPoisonBase = ReservePoisonArea(gMozillaPoisonSize);
+
+  if (gMozillaPoisonSize == 0) { // can't happen
+    return;
+  }
+  gMozillaPoisonValue = gMozillaPoisonBase + gMozillaPoisonSize / 2 - 1;
+}