1 files changed, 530 insertions, 0 deletions
diff --git a/mfbt/tests/TestPoisonArea.cpp b/mfbt/tests/TestPoisonArea.cpp
new file mode 100644
index 0000000000..9df3929834
--- /dev/null
+++ b/mfbt/tests/TestPoisonArea.cpp
@@ -0,0 +1,530 @@
+/* -*- 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/.
+ */
+
+/* Code in this file needs to be kept in sync with code in nsPresArena.cpp.
+ *
+ * We want to use a fixed address for frame poisoning so that it is readily
+ * identifiable in crash dumps.  Whether such an address is available
+ * without any special setup depends on the system configuration.
+ *
+ * All current 64-bit CPUs (with the possible exception of PowerPC64)
+ * reserve the vast majority of the virtual address space for future
+ * hardware extensions; valid addresses must be below some break point
+ * between 2**48 and 2**54, depending on exactly which chip you have.  Some
+ * chips (notably amd64) also allow the use of the *highest* 2**48 -- 2**54
+ * addresses.  Thus, if user space pointers are 64 bits wide, we can just
+ * use an address outside this range, and no more is required.  To
+ * accommodate the chips that allow very high addresses to be valid, the
+ * value chosen is close to 2**63 (that is, in the middle of the space).
+ *
+ * In most cases, a purely 32-bit operating system must reserve some
+ * fraction of the address space for its own use.  Contemporary 32-bit OSes
+ * tend to take the high gigabyte or so (0xC000_0000 on up).  If we can
+ * prove that high addresses are reserved to the kernel, we can use an
+ * address in that region.  Unfortunately, not all 32-bit OSes do this;
+ * OSX 10.4 might not, and it is unclear what mobile OSes are like
+ * (some 32-bit CPUs make it very easy for the kernel to exist in its own
+ * private address space).
+ *
+ * Furthermore, when a 32-bit user space process is running on a 64-bit
+ * kernel, the operating system has no need to reserve any of the space that
+ * the process can see, and generally does not do so.  This is the scenario
+ * of greatest concern, since it covers all contemporary OSX iterations
+ * (10.5+) as well as Windows Vista and 7 on newer amd64 hardware.  Linux on
+ * amd64 is generally run as a pure 64-bit environment, but its 32-bit
+ * compatibility mode also has this property.
+ *
+ * Thus, when user space pointers are 32 bits wide, we need to validate
+ * our chosen address, and possibly *make* it a good poison address by
+ * allocating a page around it and marking it inaccessible.  The algorithm
+ * for this is:
+ *
+ *  1. Attempt to make the page surrounding the poison address a reserved,
+ *     inaccessible memory region using OS primitives.  On Windows, this is
+ *     done with VirtualAlloc(MEM_RESERVE); on Unix, mmap(PROT_NONE).
+ *
+ *  2. If mmap/VirtualAlloc failed, there are two possible reasons: either
+ *     the region is reserved to the kernel and no further action is
+ *     required, or there is already usable memory in this area and we have
+ *     to pick a different address.  The tricky part is knowing which case
+ *     we have, without attempting to access the region.  On Windows, we
+ *     rely on GetSystemInfo()'s reported upper and lower bounds of the
+ *     application memory area.  On Unix, there is nothing devoted to the
+ *     purpose, but seeing if madvise() fails is close enough (it *might*
+ *     disrupt someone else's use of the memory region, but not by as much
+ *     as anything else available).
+ *
+ * Be aware of these gotchas:
+ *
+ * 1. We cannot use mmap() with MAP_FIXED.  MAP_FIXED is defined to
+ *    _replace_ any existing mapping in the region, if necessary to satisfy
+ *    the request.  Obviously, as we are blindly attempting to acquire a
+ *    page at a constant address, we must not do this, lest we overwrite
+ *    someone else's allocation.
+ *
+ * 2. For the same reason, we cannot blindly use mprotect() if mmap() fails.
+ *
+ * 3. madvise() may fail when applied to a 'magic' memory region provided as
+ *    a kernel/user interface.  Fortunately, the only such case I know about
+ *    is the "vsyscall" area (not to be confused with the "vdso" area) for
+ *    *64*-bit processes on Linux - and we don't even run this code for
+ *    64-bit processes.
+ *
+ * 4. VirtualQuery() does not produce any useful information if
+ *    applied to kernel memory - in fact, it doesn't write its output
+ *    at all.  Thus, it is not used here.
+ */
+
+// MAP_ANON(YMOUS) is not in any standard.  Add defines as necessary.
+#define _GNU_SOURCE 1
+#define _DARWIN_C_SOURCE 1
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef _WIN32
+#  include <windows.h>
+#else
+#  include <sys/types.h>
+#  include <unistd.h>
+#  include <sys/wait.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
+
+#define SIZxPTR ((int)(sizeof(uintptr_t) * 2))
+
+/* This program assumes that a whole number of return instructions fit into
+ * 32 bits, and that 32-bit alignment is sufficient for a branch destination.
+ * For architectures where this is not true, fiddling with RETURN_INSTR_TYPE
+ * can be enough.
+ */
+
+#if defined __i386__ || defined __x86_64__ || defined __i386 || \
+    defined __x86_64 || defined _M_IX86 || defined _M_AMD64
+#  define RETURN_INSTR 0xC3C3C3C3 /* ret; ret; ret; ret */
+
+#elif defined __arm__ || defined _M_ARM
+#  define RETURN_INSTR 0xE12FFF1E /* bx lr */
+
+// PPC has its own style of CPU-id #defines.  There is no Windows for
+// PPC as far as I know, so no _M_ variant.
+#elif defined _ARCH_PPC || defined _ARCH_PWR || defined _ARCH_PWR2
+#  define RETURN_INSTR 0x4E800020 /* blr */
+
+#elif defined __m68k__
+#  define RETURN_INSTR 0x4E754E75 /* rts; rts */
+
+#elif defined __riscv
+#  define RETURN_INSTR 0x80828082 /* ret; ret */
+
+#elif defined __sparc || defined __sparcv9
+#  define RETURN_INSTR 0x81c3e008 /* retl */
+
+#elif defined __alpha
+#  define RETURN_INSTR 0x6bfa8001 /* ret */
+
+#elif defined __hppa
+#  define RETURN_INSTR 0xe840c002 /* bv,n r0(rp) */
+
+#elif defined __mips
+#  define RETURN_INSTR 0x03e00008 /* jr ra */
+
+#  ifdef __MIPSEL
+/* On mipsel, jr ra needs to be followed by a nop.
+   0x03e00008 as a 64 bits integer just does that */
+#    define RETURN_INSTR_TYPE uint64_t
+#  endif
+
+#elif defined __s390__
+#  define RETURN_INSTR 0x07fe0000 /* br %r14 */
+
+#elif defined __sh__
+#  define RETURN_INSTR 0x0b000b00 /* rts; rts */
+
+#elif defined __aarch64__ || defined _M_ARM64
+#  define RETURN_INSTR 0xd65f03c0 /* ret */
+
+#elif defined __loongarch64
+#  define RETURN_INSTR 0x4c000020 /* jirl zero, ra, 0 */
+
+#elif defined __ia64
+struct ia64_instr {
+  uint32_t mI[4];
+};
+static const ia64_instr _return_instr = {
+    {0x00000011, 0x00000001, 0x80000200, 0x00840008}}; /* br.ret.sptk.many b0 */
+
+#  define RETURN_INSTR _return_instr
+#  define RETURN_INSTR_TYPE ia64_instr
+
+#else
+#  error "Need return instruction for this architecture"
+#endif
+
+#ifndef RETURN_INSTR_TYPE
+#  define RETURN_INSTR_TYPE uint32_t
+#endif
+
+// Miscellaneous Windows/Unix portability gumph
+
+#ifdef _WIN32
+// Uses of this function deliberately leak the string.
+static LPSTR StrW32Error(DWORD aErrcode) {
+  LPSTR errmsg;
+  FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
+                     FORMAT_MESSAGE_IGNORE_INSERTS,
+                 nullptr, aErrcode, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+                 (LPSTR)&errmsg, 0, nullptr);
+
+  // FormatMessage puts an unwanted newline at the end of the string
+  size_t n = strlen(errmsg) - 1;
+  while (errmsg[n] == '\r' || errmsg[n] == '\n') {
+    n--;
+  }
+  errmsg[n + 1] = '\0';
+  return errmsg;
+}
+#  define LastErrMsg() (StrW32Error(GetLastError()))
+
+// Because we use VirtualAlloc in MEM_RESERVE mode, the "page size" we want
+// is the allocation granularity.
+static SYSTEM_INFO sInfo_;
+
+static inline uint32_t PageSize() { return sInfo_.dwAllocationGranularity; }
+
+static void* ReserveRegion(uintptr_t aRequest, bool aAccessible) {
+  return VirtualAlloc((void*)aRequest, PageSize(),
+                      aAccessible ? MEM_RESERVE | MEM_COMMIT : MEM_RESERVE,
+                      aAccessible ? PAGE_EXECUTE_READWRITE : PAGE_NOACCESS);
+}
+
+static void ReleaseRegion(void* aPage) {
+  VirtualFree(aPage, PageSize(), MEM_RELEASE);
+}
+
+static bool ProbeRegion(uintptr_t aPage) {
+  return aPage >= (uintptr_t)sInfo_.lpMaximumApplicationAddress &&
+         aPage + PageSize() >= (uintptr_t)sInfo_.lpMaximumApplicationAddress;
+}
+
+static bool MakeRegionExecutable(void*) { return false; }
+
+#  undef MAP_FAILED
+#  define MAP_FAILED 0
+
+#else  // Unix
+
+#  define LastErrMsg() (strerror(errno))
+
+static unsigned long gUnixPageSize;
+
+static inline unsigned long PageSize() { return gUnixPageSize; }
+
+static void* ReserveRegion(uintptr_t aRequest, bool aAccessible) {
+  return mmap(reinterpret_cast<void*>(aRequest), PageSize(),
+              aAccessible ? PROT_READ | PROT_WRITE : PROT_NONE,
+              MAP_PRIVATE | MAP_ANON, -1, 0);
+}
+
+static void ReleaseRegion(void* aPage) { munmap(aPage, PageSize()); }
+
+static bool ProbeRegion(uintptr_t aPage) {
+#  ifdef XP_SOLARIS
+  return !!posix_madvise(reinterpret_cast<void*>(aPage), PageSize(),
+                         POSIX_MADV_NORMAL);
+#  else
+  return !!madvise(reinterpret_cast<void*>(aPage), PageSize(), MADV_NORMAL);
+#  endif
+}
+
+static int MakeRegionExecutable(void* aPage) {
+  return mprotect((caddr_t)aPage, PageSize(),
+                  PROT_READ | PROT_WRITE | PROT_EXEC);
+}
+
+#endif
+
+static uintptr_t ReservePoisonArea() {
+  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.
+    uintptr_t result =
+        (((uintptr_t(0x7FFFFFFFu) << 31) << 1 | uintptr_t(0xF0DEAFFFu)) &
+         ~uintptr_t(PageSize() - 1));
+    printf("INFO | poison area assumed at 0x%.*" PRIxPTR "\n", SIZxPTR, result);
+    return result;
+  }
+
+  // First see if we can allocate the preferred poison address from the OS.
+  uintptr_t candidate = (0xF0DEAFFF & ~(PageSize() - 1));
+  void* result = ReserveRegion(candidate, false);
+  if (result == reinterpret_cast<void*>(candidate)) {
+    // success - inaccessible page allocated
+    printf("INFO | poison area allocated at 0x%.*" PRIxPTR
+           " (preferred addr)\n",
+           SIZxPTR, reinterpret_cast<uintptr_t>(result));
+    return candidate;
+  }
+
+  // That didn't work, so see if the preferred address is within a range
+  // of permanently inacessible memory.
+  if (ProbeRegion(candidate)) {
+    // success - selected page cannot be usable memory
+    if (result != MAP_FAILED) {
+      ReleaseRegion(result);
+    }
+    printf("INFO | poison area assumed at 0x%.*" PRIxPTR " (preferred addr)\n",
+           SIZxPTR, candidate);
+    return candidate;
+  }
+
+  // The preferred address is already in use.  Did the OS give us a
+  // consolation prize?
+  if (result != MAP_FAILED) {
+    uintptr_t ures = reinterpret_cast<uintptr_t>(result);
+    printf("INFO | poison area allocated at 0x%.*" PRIxPTR
+           " (consolation prize)\n",
+           SIZxPTR, ures);
+    return ures;
+  }
+
+  // It didn't, so try to allocate again, without any constraint on
+  // the address.
+  result = ReserveRegion(0, false);
+  if (result != MAP_FAILED) {
+    uintptr_t ures = reinterpret_cast<uintptr_t>(result);
+    printf("INFO | poison area allocated at 0x%.*" PRIxPTR " (fallback)\n",
+           SIZxPTR, ures);
+    return ures;
+  }
+
+  printf("ERROR | no usable poison area found\n");
+  return 0;
+}
+
+/* The "positive control" area confirms that we can allocate a page with the
+ * proper characteristics.
+ */
+static uintptr_t ReservePositiveControl() {
+  void* result = ReserveRegion(0, false);
+  if (result == MAP_FAILED) {
+    printf("ERROR | allocating positive control | %s\n", LastErrMsg());
+    return 0;
+  }
+  printf("INFO | positive control allocated at 0x%.*" PRIxPTR "\n", SIZxPTR,
+         (uintptr_t)result);
+  return (uintptr_t)result;
+}
+
+/* The "negative control" area confirms that our probe logic does detect a
+ * page that is readable, writable, or executable.
+ */
+static uintptr_t ReserveNegativeControl() {
+  void* result = ReserveRegion(0, true);
+  if (result == MAP_FAILED) {
+    printf("ERROR | allocating negative control | %s\n", LastErrMsg());
+    return 0;
+  }
+
+  // Fill the page with return instructions.
+  RETURN_INSTR_TYPE* p = reinterpret_cast<RETURN_INSTR_TYPE*>(result);
+  RETURN_INSTR_TYPE* limit = reinterpret_cast<RETURN_INSTR_TYPE*>(
+      reinterpret_cast<char*>(result) + PageSize());
+  while (p < limit) {
+    *p++ = RETURN_INSTR;
+  }
+
+  // Now mark it executable as well as readable and writable.
+  // (mmap(PROT_EXEC) may fail when applied to anonymous memory.)
+
+  if (MakeRegionExecutable(result)) {
+    printf("ERROR | making negative control executable | %s\n", LastErrMsg());
+    return 0;
+  }
+
+  printf("INFO | negative control allocated at 0x%.*" PRIxPTR "\n", SIZxPTR,
+         (uintptr_t)result);
+  return (uintptr_t)result;
+}
+
+#ifndef _WIN32
+static void JumpTo(uintptr_t aOpaddr) {
+#  ifdef __ia64
+  struct func_call {
+    uintptr_t mFunc;
+    uintptr_t mGp;
+  } call = {
+      aOpaddr,
+  };
+  ((void (*)()) & call)();
+#  else
+  ((void (*)())aOpaddr)();
+#  endif
+}
+#endif
+
+/* Test each page.  */
+static bool TestPage(const char* aPageLabel, uintptr_t aPageAddr,
+                     int aShouldSucceed) {
+  const char* oplabel;
+  uintptr_t opaddr;
+
+  bool failed = false;
+  for (unsigned int test = 0; test < 3; test++) {
+    switch (test) {
+        // The execute test must be done before the write test, because the
+        // write test will clobber memory at the target address.
+      case 0:
+        oplabel = "reading";
+        opaddr = aPageAddr + PageSize() / 2 - 1;
+        break;
+      case 1:
+        oplabel = "executing";
+        opaddr = aPageAddr + PageSize() / 2;
+        break;
+      case 2:
+        oplabel = "writing";
+        opaddr = aPageAddr + PageSize() / 2 - 1;
+        break;
+      default:
+        abort();
+    }
+
+#ifdef _WIN32
+    bool badptr = true;
+    MEMORY_BASIC_INFORMATION mbi = {};
+
+    if (VirtualQuery((LPCVOID)opaddr, &mbi, sizeof(mbi)) &&
+        mbi.State == MEM_COMMIT) {
+      switch (test) {
+        case 0:  // read
+          badptr = !(mbi.Protect & (PAGE_EXECUTE_READ | PAGE_EXECUTE_READWRITE |
+                                    PAGE_READONLY | PAGE_READWRITE));
+          break;
+        case 1:  // execute
+          badptr =
+              !(mbi.Protect & (PAGE_EXECUTE_READ | PAGE_EXECUTE_READWRITE));
+          break;
+        case 2:  // write
+          badptr = !(mbi.Protect & (PAGE_READWRITE | PAGE_EXECUTE_READWRITE));
+          break;
+        default:
+          abort();
+      }
+    }
+
+    if (badptr) {
+      if (aShouldSucceed) {
+        printf("TEST-UNEXPECTED-FAIL | %s %s\n", oplabel, aPageLabel);
+        failed = true;
+      } else {
+        printf("TEST-PASS | %s %s\n", oplabel, aPageLabel);
+      }
+    } else {
+      // if control reaches this point the probe succeeded
+      if (aShouldSucceed) {
+        printf("TEST-PASS | %s %s\n", oplabel, aPageLabel);
+      } else {
+        printf("TEST-UNEXPECTED-FAIL | %s %s\n", oplabel, aPageLabel);
+        failed = true;
+      }
+    }
+#else
+    pid_t pid = fork();
+    if (pid == -1) {
+      printf("ERROR | %s %s | fork=%s\n", oplabel, aPageLabel, LastErrMsg());
+      exit(2);
+    } else if (pid == 0) {
+      volatile unsigned char scratch;
+      switch (test) {
+        case 0:
+          scratch = *(volatile unsigned char*)opaddr;
+          break;
+        case 1:
+          JumpTo(opaddr);
+          break;
+        case 2:
+          *(volatile unsigned char*)opaddr = 0;
+          break;
+        default:
+          abort();
+      }
+      (void)scratch;
+      _exit(0);
+    } else {
+      int status;
+      if (waitpid(pid, &status, 0) != pid) {
+        printf("ERROR | %s %s | wait=%s\n", oplabel, aPageLabel, LastErrMsg());
+        exit(2);
+      }
+
+      if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+        if (aShouldSucceed) {
+          printf("TEST-PASS | %s %s\n", oplabel, aPageLabel);
+        } else {
+          printf("TEST-UNEXPECTED-FAIL | %s %s | unexpected successful exit\n",
+                 oplabel, aPageLabel);
+          failed = true;
+        }
+      } else if (WIFEXITED(status)) {
+        printf("ERROR | %s %s | unexpected exit code %d\n", oplabel, aPageLabel,
+               WEXITSTATUS(status));
+        exit(2);
+      } else if (WIFSIGNALED(status)) {
+        if (aShouldSucceed) {
+          printf("TEST-UNEXPECTED-FAIL | %s %s | unexpected signal %d\n",
+                 oplabel, aPageLabel, WTERMSIG(status));
+          failed = true;
+        } else {
+          printf("TEST-PASS | %s %s | signal %d (as expected)\n", oplabel,
+                 aPageLabel, WTERMSIG(status));
+        }
+      } else {
+        printf("ERROR | %s %s | unexpected exit status %d\n", oplabel,
+               aPageLabel, status);
+        exit(2);
+      }
+    }
+#endif
+  }
+  return failed;
+}
+
+int main() {
+#ifdef _WIN32
+  GetSystemInfo(&sInfo_);
+#else
+  gUnixPageSize = sysconf(_SC_PAGESIZE);
+#endif
+
+  uintptr_t ncontrol = ReserveNegativeControl();
+  uintptr_t pcontrol = ReservePositiveControl();
+  uintptr_t poison = ReservePoisonArea();
+
+  if (!ncontrol || !pcontrol || !poison) {
+    return 2;
+  }
+
+  bool failed = false;
+  failed |= TestPage("negative control", ncontrol, 1);
+  failed |= TestPage("positive control", pcontrol, 0);
+  failed |= TestPage("poison area", poison, 0);
+
+  return failed ? 1 : 0;
+}