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/* -*- 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
*/
/* 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;
}