1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
8 /* Code in this file needs to be kept in sync with code in nsPresArena.cpp.
10 * We want to use a fixed address for frame poisoning so that it is readily
11 * identifiable in crash dumps. Whether such an address is available
12 * without any special setup depends on the system configuration.
14 * All current 64-bit CPUs (with the possible exception of PowerPC64)
15 * reserve the vast majority of the virtual address space for future
16 * hardware extensions; valid addresses must be below some break point
17 * between 2**48 and 2**54, depending on exactly which chip you have. Some
18 * chips (notably amd64) also allow the use of the *highest* 2**48 -- 2**54
19 * addresses. Thus, if user space pointers are 64 bits wide, we can just
20 * use an address outside this range, and no more is required. To
21 * accommodate the chips that allow very high addresses to be valid, the
22 * value chosen is close to 2**63 (that is, in the middle of the space).
24 * In most cases, a purely 32-bit operating system must reserve some
25 * fraction of the address space for its own use. Contemporary 32-bit OSes
26 * tend to take the high gigabyte or so (0xC000_0000 on up). If we can
27 * prove that high addresses are reserved to the kernel, we can use an
28 * address in that region. Unfortunately, not all 32-bit OSes do this;
29 * OSX 10.4 might not, and it is unclear what mobile OSes are like
30 * (some 32-bit CPUs make it very easy for the kernel to exist in its own
31 * private address space).
33 * Furthermore, when a 32-bit user space process is running on a 64-bit
34 * kernel, the operating system has no need to reserve any of the space that
35 * the process can see, and generally does not do so. This is the scenario
36 * of greatest concern, since it covers all contemporary OSX iterations
37 * (10.5+) as well as Windows Vista and 7 on newer amd64 hardware. Linux on
38 * amd64 is generally run as a pure 64-bit environment, but its 32-bit
39 * compatibility mode also has this property.
41 * Thus, when user space pointers are 32 bits wide, we need to validate
42 * our chosen address, and possibly *make* it a good poison address by
43 * allocating a page around it and marking it inaccessible. The algorithm
46 * 1. Attempt to make the page surrounding the poison address a reserved,
47 * inaccessible memory region using OS primitives. On Windows, this is
48 * done with VirtualAlloc(MEM_RESERVE); on Unix, mmap(PROT_NONE).
50 * 2. If mmap/VirtualAlloc failed, there are two possible reasons: either
51 * the region is reserved to the kernel and no further action is
52 * required, or there is already usable memory in this area and we have
53 * to pick a different address. The tricky part is knowing which case
54 * we have, without attempting to access the region. On Windows, we
55 * rely on GetSystemInfo()'s reported upper and lower bounds of the
56 * application memory area. On Unix, there is nothing devoted to the
57 * purpose, but seeing if madvise() fails is close enough (it *might*
58 * disrupt someone else's use of the memory region, but not by as much
59 * as anything else available).
61 * Be aware of these gotchas:
63 * 1. We cannot use mmap() with MAP_FIXED. MAP_FIXED is defined to
64 * _replace_ any existing mapping in the region, if necessary to satisfy
65 * the request. Obviously, as we are blindly attempting to acquire a
66 * page at a constant address, we must not do this, lest we overwrite
67 * someone else's allocation.
69 * 2. For the same reason, we cannot blindly use mprotect() if mmap() fails.
71 * 3. madvise() may fail when applied to a 'magic' memory region provided as
72 * a kernel/user interface. Fortunately, the only such case I know about
73 * is the "vsyscall" area (not to be confused with the "vdso" area) for
74 * *64*-bit processes on Linux - and we don't even run this code for
77 * 4. VirtualQuery() does not produce any useful information if
78 * applied to kernel memory - in fact, it doesn't write its output
79 * at all. Thus, it is not used here.
82 // MAP_ANON(YMOUS) is not in any standard. Add defines as necessary.
84 #define _DARWIN_C_SOURCE 1
95 # include <sys/types.h>
97 # include <sys/wait.h>
99 # include <sys/mman.h>
101 # ifdef MAP_ANONYMOUS
102 # define MAP_ANON MAP_ANONYMOUS
104 # error "Don't know how to get anonymous memory"
109 #define SIZxPTR ((int)(sizeof(uintptr_t) * 2))
111 /* This program assumes that a whole number of return instructions fit into
112 * 32 bits, and that 32-bit alignment is sufficient for a branch destination.
113 * For architectures where this is not true, fiddling with RETURN_INSTR_TYPE
117 #if defined __i386__ || defined __x86_64__ || defined __i386 || \
118 defined __x86_64 || defined _M_IX86 || defined _M_AMD64
119 # define RETURN_INSTR 0xC3C3C3C3 /* ret; ret; ret; ret */
121 #elif defined __arm__ || defined _M_ARM
122 # define RETURN_INSTR 0xE12FFF1E /* bx lr */
124 // PPC has its own style of CPU-id #defines. There is no Windows for
125 // PPC as far as I know, so no _M_ variant.
126 #elif defined _ARCH_PPC || defined _ARCH_PWR || defined _ARCH_PWR2
127 # define RETURN_INSTR 0x4E800020 /* blr */
129 #elif defined __m68k__
130 # define RETURN_INSTR 0x4E754E75 /* rts; rts */
132 #elif defined __riscv
133 # define RETURN_INSTR 0x80828082 /* ret; ret */
135 #elif defined __sparc || defined __sparcv9
136 # define RETURN_INSTR 0x81c3e008 /* retl */
138 #elif defined __alpha
139 # define RETURN_INSTR 0x6bfa8001 /* ret */
142 # define RETURN_INSTR 0xe840c002 /* bv,n r0(rp) */
145 # define RETURN_INSTR 0x03e00008 /* jr ra */
148 /* On mipsel, jr ra needs to be followed by a nop.
149 0x03e00008 as a 64 bits integer just does that */
150 # define RETURN_INSTR_TYPE uint64_t
153 #elif defined __s390__
154 # define RETURN_INSTR 0x07fe0000 /* br %r14 */
157 # define RETURN_INSTR 0x0b000b00 /* rts; rts */
159 #elif defined __aarch64__ || defined _M_ARM64
160 # define RETURN_INSTR 0xd65f03c0 /* ret */
162 #elif defined __loongarch64
163 # define RETURN_INSTR 0x4c000020 /* jirl zero, ra, 0 */
169 static const ia64_instr _return_instr
= {
170 {0x00000011, 0x00000001, 0x80000200, 0x00840008}}; /* br.ret.sptk.many b0 */
172 # define RETURN_INSTR _return_instr
173 # define RETURN_INSTR_TYPE ia64_instr
176 # error "Need return instruction for this architecture"
179 #ifndef RETURN_INSTR_TYPE
180 # define RETURN_INSTR_TYPE uint32_t
183 // Miscellaneous Windows/Unix portability gumph
186 // Uses of this function deliberately leak the string.
187 static LPSTR
StrW32Error(DWORD aErrcode
) {
189 FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER
| FORMAT_MESSAGE_FROM_SYSTEM
|
190 FORMAT_MESSAGE_IGNORE_INSERTS
,
191 nullptr, aErrcode
, MAKELANGID(LANG_NEUTRAL
, SUBLANG_DEFAULT
),
192 (LPSTR
)&errmsg
, 0, nullptr);
194 // FormatMessage puts an unwanted newline at the end of the string
195 size_t n
= strlen(errmsg
) - 1;
196 while (errmsg
[n
] == '\r' || errmsg
[n
] == '\n') {
199 errmsg
[n
+ 1] = '\0';
202 # define LastErrMsg() (StrW32Error(GetLastError()))
204 // Because we use VirtualAlloc in MEM_RESERVE mode, the "page size" we want
205 // is the allocation granularity.
206 static SYSTEM_INFO sInfo_
;
208 static inline uint32_t PageSize() { return sInfo_
.dwAllocationGranularity
; }
210 static void* ReserveRegion(uintptr_t aRequest
, bool aAccessible
) {
211 return VirtualAlloc((void*)aRequest
, PageSize(),
212 aAccessible
? MEM_RESERVE
| MEM_COMMIT
: MEM_RESERVE
,
213 aAccessible
? PAGE_EXECUTE_READWRITE
: PAGE_NOACCESS
);
216 static void ReleaseRegion(void* aPage
) {
217 VirtualFree(aPage
, PageSize(), MEM_RELEASE
);
220 static bool ProbeRegion(uintptr_t aPage
) {
221 return aPage
>= (uintptr_t)sInfo_
.lpMaximumApplicationAddress
&&
222 aPage
+ PageSize() >= (uintptr_t)sInfo_
.lpMaximumApplicationAddress
;
225 static bool MakeRegionExecutable(void*) { return false; }
228 # define MAP_FAILED 0
232 # define LastErrMsg() (strerror(errno))
234 static unsigned long gUnixPageSize
;
236 static inline unsigned long PageSize() { return gUnixPageSize
; }
238 static void* ReserveRegion(uintptr_t aRequest
, bool aAccessible
) {
239 return mmap(reinterpret_cast<void*>(aRequest
), PageSize(),
240 aAccessible
? PROT_READ
| PROT_WRITE
: PROT_NONE
,
241 MAP_PRIVATE
| MAP_ANON
, -1, 0);
244 static void ReleaseRegion(void* aPage
) { munmap(aPage
, PageSize()); }
246 static bool ProbeRegion(uintptr_t aPage
) {
248 return !!posix_madvise(reinterpret_cast<void*>(aPage
), PageSize(),
251 return !!madvise(reinterpret_cast<void*>(aPage
), PageSize(), MADV_NORMAL
);
255 static int MakeRegionExecutable(void* aPage
) {
256 return mprotect((caddr_t
)aPage
, PageSize(),
257 PROT_READ
| PROT_WRITE
| PROT_EXEC
);
262 static uintptr_t ReservePoisonArea() {
263 if (sizeof(uintptr_t) == 8) {
264 // Use the hardware-inaccessible region.
265 // We have to avoid 64-bit constants and shifts by 32 bits, since this
266 // code is compiled in 32-bit mode, although it is never executed there.
268 (((uintptr_t(0x7FFFFFFFu
) << 31) << 1 | uintptr_t(0xF0DEAFFFu
)) &
269 ~uintptr_t(PageSize() - 1));
270 printf("INFO | poison area assumed at 0x%.*" PRIxPTR
"\n", SIZxPTR
, result
);
274 // First see if we can allocate the preferred poison address from the OS.
275 uintptr_t candidate
= (0xF0DEAFFF & ~(PageSize() - 1));
276 void* result
= ReserveRegion(candidate
, false);
277 if (result
== reinterpret_cast<void*>(candidate
)) {
278 // success - inaccessible page allocated
279 printf("INFO | poison area allocated at 0x%.*" PRIxPTR
280 " (preferred addr)\n",
281 SIZxPTR
, reinterpret_cast<uintptr_t>(result
));
285 // That didn't work, so see if the preferred address is within a range
286 // of permanently inacessible memory.
287 if (ProbeRegion(candidate
)) {
288 // success - selected page cannot be usable memory
289 if (result
!= MAP_FAILED
) {
290 ReleaseRegion(result
);
292 printf("INFO | poison area assumed at 0x%.*" PRIxPTR
" (preferred addr)\n",
297 // The preferred address is already in use. Did the OS give us a
298 // consolation prize?
299 if (result
!= MAP_FAILED
) {
300 uintptr_t ures
= reinterpret_cast<uintptr_t>(result
);
301 printf("INFO | poison area allocated at 0x%.*" PRIxPTR
302 " (consolation prize)\n",
307 // It didn't, so try to allocate again, without any constraint on
309 result
= ReserveRegion(0, false);
310 if (result
!= MAP_FAILED
) {
311 uintptr_t ures
= reinterpret_cast<uintptr_t>(result
);
312 printf("INFO | poison area allocated at 0x%.*" PRIxPTR
" (fallback)\n",
317 printf("ERROR | no usable poison area found\n");
321 /* The "positive control" area confirms that we can allocate a page with the
322 * proper characteristics.
324 static uintptr_t ReservePositiveControl() {
325 void* result
= ReserveRegion(0, false);
326 if (result
== MAP_FAILED
) {
327 printf("ERROR | allocating positive control | %s\n", LastErrMsg());
330 printf("INFO | positive control allocated at 0x%.*" PRIxPTR
"\n", SIZxPTR
,
332 return (uintptr_t)result
;
335 /* The "negative control" area confirms that our probe logic does detect a
336 * page that is readable, writable, or executable.
338 static uintptr_t ReserveNegativeControl() {
339 void* result
= ReserveRegion(0, true);
340 if (result
== MAP_FAILED
) {
341 printf("ERROR | allocating negative control | %s\n", LastErrMsg());
345 // Fill the page with return instructions.
346 RETURN_INSTR_TYPE
* p
= reinterpret_cast<RETURN_INSTR_TYPE
*>(result
);
347 RETURN_INSTR_TYPE
* limit
= reinterpret_cast<RETURN_INSTR_TYPE
*>(
348 reinterpret_cast<char*>(result
) + PageSize());
353 // Now mark it executable as well as readable and writable.
354 // (mmap(PROT_EXEC) may fail when applied to anonymous memory.)
356 if (MakeRegionExecutable(result
)) {
357 printf("ERROR | making negative control executable | %s\n", LastErrMsg());
361 printf("INFO | negative control allocated at 0x%.*" PRIxPTR
"\n", SIZxPTR
,
363 return (uintptr_t)result
;
367 static void JumpTo(uintptr_t aOpaddr
) {
375 ((void (*)()) & call
)();
377 ((void (*)())aOpaddr
)();
382 /* Test each page. */
383 static bool TestPage(const char* aPageLabel
, uintptr_t aPageAddr
,
384 int aShouldSucceed
) {
389 for (unsigned int test
= 0; test
< 3; test
++) {
391 // The execute test must be done before the write test, because the
392 // write test will clobber memory at the target address.
395 opaddr
= aPageAddr
+ PageSize() / 2 - 1;
398 oplabel
= "executing";
399 opaddr
= aPageAddr
+ PageSize() / 2;
403 opaddr
= aPageAddr
+ PageSize() / 2 - 1;
411 MEMORY_BASIC_INFORMATION mbi
= {};
413 if (VirtualQuery((LPCVOID
)opaddr
, &mbi
, sizeof(mbi
)) &&
414 mbi
.State
== MEM_COMMIT
) {
417 badptr
= !(mbi
.Protect
& (PAGE_EXECUTE_READ
| PAGE_EXECUTE_READWRITE
|
418 PAGE_READONLY
| PAGE_READWRITE
));
422 !(mbi
.Protect
& (PAGE_EXECUTE_READ
| PAGE_EXECUTE_READWRITE
));
425 badptr
= !(mbi
.Protect
& (PAGE_READWRITE
| PAGE_EXECUTE_READWRITE
));
433 if (aShouldSucceed
) {
434 printf("TEST-UNEXPECTED-FAIL | %s %s\n", oplabel
, aPageLabel
);
437 printf("TEST-PASS | %s %s\n", oplabel
, aPageLabel
);
440 // if control reaches this point the probe succeeded
441 if (aShouldSucceed
) {
442 printf("TEST-PASS | %s %s\n", oplabel
, aPageLabel
);
444 printf("TEST-UNEXPECTED-FAIL | %s %s\n", oplabel
, aPageLabel
);
451 printf("ERROR | %s %s | fork=%s\n", oplabel
, aPageLabel
, LastErrMsg());
453 } else if (pid
== 0) {
454 volatile unsigned char scratch
;
457 scratch
= *(volatile unsigned char*)opaddr
;
463 *(volatile unsigned char*)opaddr
= 0;
472 if (waitpid(pid
, &status
, 0) != pid
) {
473 printf("ERROR | %s %s | wait=%s\n", oplabel
, aPageLabel
, LastErrMsg());
477 if (WIFEXITED(status
) && WEXITSTATUS(status
) == 0) {
478 if (aShouldSucceed
) {
479 printf("TEST-PASS | %s %s\n", oplabel
, aPageLabel
);
481 printf("TEST-UNEXPECTED-FAIL | %s %s | unexpected successful exit\n",
482 oplabel
, aPageLabel
);
485 } else if (WIFEXITED(status
)) {
486 printf("ERROR | %s %s | unexpected exit code %d\n", oplabel
, aPageLabel
,
487 WEXITSTATUS(status
));
489 } else if (WIFSIGNALED(status
)) {
490 if (aShouldSucceed
) {
491 printf("TEST-UNEXPECTED-FAIL | %s %s | unexpected signal %d\n",
492 oplabel
, aPageLabel
, WTERMSIG(status
));
495 printf("TEST-PASS | %s %s | signal %d (as expected)\n", oplabel
,
496 aPageLabel
, WTERMSIG(status
));
499 printf("ERROR | %s %s | unexpected exit status %d\n", oplabel
,
511 GetSystemInfo(&sInfo_
);
513 gUnixPageSize
= sysconf(_SC_PAGESIZE
);
516 uintptr_t ncontrol
= ReserveNegativeControl();
517 uintptr_t pcontrol
= ReservePositiveControl();
518 uintptr_t poison
= ReservePoisonArea();
520 if (!ncontrol
|| !pcontrol
|| !poison
) {
525 failed
|= TestPage("negative control", ncontrol
, 1);
526 failed
|= TestPage("positive control", pcontrol
, 0);
527 failed
|= TestPage("poison area", poison
, 0);
529 return failed
? 1 : 0;