path: root/mfbt/tests/TestPoisonArea.cpp

/* -*- 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;
}