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 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

 /* vim:set ts=2 sw=2 sts=2 et cindent: */

 /* 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.

  */

 #include "mozilla/IntegerPrintfMacros.h"

 #include "mozilla/NullPtr.h"

 // MAP_ANON(YMOUS) is not in any standard.  Add defines as necessary.

 #define _GNU_SOURCE 1

 #define _DARWIN_C_SOURCE 1

 #include <stddef.h>

 #include <errno.h>

 #include <stdio.h>

 #include <stdlib.h>

 #include <string.h>

 #ifdef _WIN32

 #include <windows.h>

 #else

 #include <sys/types.h>

 #include <fcntl.h>

 #include <signal.h>

 #include <unistd.h>

 #include <sys/stat.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 __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 __aarch64__

 #define RETURN_INSTR 0xd65f03c0 /* ret */

 #elif defined __ia64

 struct ia64_instr { uint32_t i[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 errcode)

 {

   LPSTR errmsg;

   FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER |

                  FORMAT_MESSAGE_FROM_SYSTEM |

                  FORMAT_MESSAGE_IGNORE_INSERTS,

                  nullptr, errcode, 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;

 #undef PAGESIZE

 #define PAGESIZE (_sinfo.dwAllocationGranularity)

 static void *

 ReserveRegion(uintptr_t request, bool accessible)

 {

   return VirtualAlloc((void *)request, PAGESIZE,

                       accessible ? MEM_RESERVE|MEM_COMMIT : MEM_RESERVE,

                       accessible ? PAGE_EXECUTE_READWRITE : PAGE_NOACCESS);

 }

 static void

 ReleaseRegion(void *page)

 {

   VirtualFree(page, PAGESIZE, MEM_RELEASE);

 }

 static bool

 ProbeRegion(uintptr_t page)

 {

   if (page >= (uintptr_t)_sinfo.lpMaximumApplicationAddress &&

       page + PAGESIZE >= (uintptr_t)_sinfo.lpMaximumApplicationAddress) {

     return true;

   } else {

     return false;

   }

 }

 static bool

 MakeRegionExecutable(void *)

 {

   return false;

 }

 #undef MAP_FAILED

 #define MAP_FAILED 0

 #else // Unix

 #define LastErrMsg() (strerror(errno))

 static unsigned long _pagesize;

 #define PAGESIZE _pagesize

 static void *

 ReserveRegion(uintptr_t request, bool accessible)

 {

   return mmap(reinterpret_cast<void*>(request), PAGESIZE,

               accessible ? PROT_READ|PROT_WRITE : PROT_NONE,

               MAP_PRIVATE|MAP_ANON, -1, 0);

 }

 static void

 ReleaseRegion(void *page)

 {

   munmap(page, PAGESIZE);

 }

 static bool

 ProbeRegion(uintptr_t page)

 {

   if (madvise(reinterpret_cast<void*>(page), PAGESIZE, MADV_NORMAL)) {

     return true;

   } else {

     return false;

   }

 }

 static int

 MakeRegionExecutable(void *page)

 {

   return mprotect((caddr_t)page, 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;

   } else {

     // 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 == (void *)candidate) {

       // success - inaccessible page allocated

       printf("INFO | poison area allocated at 0x%.*" PRIxPTR

              " (preferred addr)\n", SIZxPTR, (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) {

       printf("INFO | poison area allocated at 0x%.*" PRIxPTR

              " (consolation prize)\n", SIZxPTR, (uintptr_t)result);

       return (uintptr_t)result;

     }

     // It didn't, so try to allocate again, without any constraint on

     // the address.

     result = ReserveRegion(0, false);

     if (result != MAP_FAILED) {

       printf("INFO | poison area allocated at 0x%.*" PRIxPTR

              " (fallback)\n", SIZxPTR, (uintptr_t)result);

       return (uintptr_t)result;

     }

     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 = (RETURN_INSTR_TYPE *)result;

   RETURN_INSTR_TYPE *limit = (RETURN_INSTR_TYPE *)(((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;

 }

 static void

 JumpTo(uintptr_t opaddr)

 {

 #ifdef __ia64

   struct func_call {

     uintptr_t func;

     uintptr_t gp;

   } call = { opaddr, };

   ((void (*)())&call)();

 #else

   ((void (*)())opaddr)();

 #endif

 }

 #ifdef _WIN32

 static BOOL

 IsBadExecPtr(uintptr_t ptr)

 {

   BOOL ret = false;

 #ifdef _MSC_VER

   __try {

     JumpTo(ptr);

   } __except (EXCEPTION_EXECUTE_HANDLER) {

     ret = true;

   }

 #else

   printf("INFO | exec test not supported on MinGW build\n");

   // We do our best

   ret = IsBadReadPtr((const void*)ptr, 1);

 #endif

   return ret;

 }

 #endif

 /* Test each page.  */

 static bool

 TestPage(const char *pagelabel, uintptr_t pageaddr, int should_succeed)

 {

   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 = pageaddr + PAGESIZE/2 - 1; break;

     case 1: oplabel = "executing"; opaddr = pageaddr + PAGESIZE/2; break;

     case 2: oplabel = "writing"; opaddr = pageaddr + PAGESIZE/2 - 1; break;

     default: abort();

     }

 #ifdef _WIN32

     BOOL badptr;

     switch (test) {

     case 0: badptr = IsBadReadPtr((const void*)opaddr, 1); break;

     case 1: badptr = IsBadExecPtr(opaddr); break;

     case 2: badptr = IsBadWritePtr((void*)opaddr, 1); break;

     default: abort();

     }

     if (badptr) {

       if (should_succeed) {

         printf("TEST-UNEXPECTED-FAIL | %s %s\n", oplabel, pagelabel);

         failed = true;

       } else {

         printf("TEST-PASS | %s %s\n", oplabel, pagelabel);

       }

     } else {

       // if control reaches this point the probe succeeded

       if (should_succeed) {

         printf("TEST-PASS | %s %s\n", oplabel, pagelabel);

       } else {

         printf("TEST-UNEXPECTED-FAIL | %s %s\n", oplabel, pagelabel);

         failed = true;

       }

     }

 #else

     pid_t pid = fork();

     if (pid == -1) {

       printf("ERROR | %s %s | fork=%s\n", oplabel, pagelabel,

              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, pagelabel,

                LastErrMsg());

         exit(2);

       }

       if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {

         if (should_succeed) {

           printf("TEST-PASS | %s %s\n", oplabel, pagelabel);

         } else {

           printf("TEST-UNEXPECTED-FAIL | %s %s | unexpected successful exit\n",

                  oplabel, pagelabel);

           failed = true;

         }

       } else if (WIFEXITED(status)) {

         printf("ERROR | %s %s | unexpected exit code %d\n",

                oplabel, pagelabel, WEXITSTATUS(status));

         exit(2);

       } else if (WIFSIGNALED(status)) {

         if (should_succeed) {

           printf("TEST-UNEXPECTED-FAIL | %s %s | unexpected signal %d\n",

                  oplabel, pagelabel, WTERMSIG(status));

           failed = true;

         } else {

           printf("TEST-PASS | %s %s | signal %d (as expected)\n",

                  oplabel, pagelabel, WTERMSIG(status));

         }

       } else {

         printf("ERROR | %s %s | unexpected exit status %d\n",

                oplabel, pagelabel, status);

         exit(2);

       }

     }

 #endif

   }

   return failed;

 }

 int

 main()

 {

 #ifdef _WIN32

   GetSystemInfo(&_sinfo);

 #else

   _pagesize = 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;

 }