vendor/compiler_builtins/compiler-rt/lib/cfi/cfi.cc

   1 //===-------- cfi.cc ------------------------------------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the runtime support for the cross-DSO CFI.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include <assert.h>
  15 #include <elf.h>
  16
  17 #include "sanitizer_common/sanitizer_common.h"
  18 #if SANITIZER_FREEBSD
  19 #include <sys/link_elf.h>
  20 #endif
  21 #include <link.h>
  22 #include <string.h>
  23 #include <stdlib.h>
  24 #include <sys/mman.h>
  25
  26 #if SANITIZER_LINUX
  27 typedef ElfW(Phdr) Elf_Phdr;
  28 typedef ElfW(Ehdr) Elf_Ehdr;
  29 typedef ElfW(Addr) Elf_Addr;
  30 typedef ElfW(Sym) Elf_Sym;
  31 typedef ElfW(Dyn) Elf_Dyn;
  32 #elif SANITIZER_FREEBSD
  33 #if SANITIZER_WORDSIZE == 64
  34 #define ElfW64_Dyn Elf_Dyn
  35 #define ElfW64_Sym Elf_Sym
  36 #else
  37 #define ElfW32_Dyn Elf_Dyn
  38 #define ElfW32_Sym Elf_Sym
  39 #endif
  40 #endif
  41
  42 #include "interception/interception.h"
  43 #include "sanitizer_common/sanitizer_flag_parser.h"
  44 #include "ubsan/ubsan_init.h"
  45 #include "ubsan/ubsan_flags.h"
  46
  47 #ifdef CFI_ENABLE_DIAG
  48 #include "ubsan/ubsan_handlers.h"
  49 #endif
  50
  51 using namespace __sanitizer;
  52
  53 namespace __cfi {
  54
  55 #define kCfiShadowLimitsStorageSize 4096 // 1 page
  56 // Lets hope that the data segment is mapped with 4K pages.
  57 // The pointer to the cfi shadow region is stored at the start of this page.
  58 // The rest of the page is unused and re-mapped read-only.
  59 static union {
  60   char space[kCfiShadowLimitsStorageSize];
  61   struct {
  62     uptr start;
  63     uptr size;
  64   } limits;
  65 } cfi_shadow_limits_storage
  66     __attribute__((aligned(kCfiShadowLimitsStorageSize)));
  67 static constexpr uptr kShadowGranularity = 12;
  68 static constexpr uptr kShadowAlign = 1UL << kShadowGranularity; // 4096
  69
  70 static constexpr uint16_t kInvalidShadow = 0;
  71 static constexpr uint16_t kUncheckedShadow = 0xFFFFU;
  72
  73 // Get the start address of the CFI shadow region.
  74 uptr GetShadow() {
  75   return cfi_shadow_limits_storage.limits.start;
  76 }
  77
  78 uptr GetShadowSize() {
  79   return cfi_shadow_limits_storage.limits.size;
  80 }
  81
  82 // This will only work while the shadow is not allocated.
  83 void SetShadowSize(uptr size) {
  84   cfi_shadow_limits_storage.limits.size = size;
  85 }
  86
  87 uptr MemToShadowOffset(uptr x) {
  88   return (x >> kShadowGranularity) << 1;
  89 }
  90
  91 uint16_t *MemToShadow(uptr x, uptr shadow_base) {
  92   return (uint16_t *)(shadow_base + MemToShadowOffset(x));
  93 }
  94
  95 typedef int (*CFICheckFn)(u64, void *, void *);
  96
  97 // This class reads and decodes the shadow contents.
  98 class ShadowValue {
  99   uptr addr;
 100   uint16_t v;
 101   explicit ShadowValue(uptr addr, uint16_t v) : addr(addr), v(v) {}
 102
 103 public:
 104   bool is_invalid() const { return v == kInvalidShadow; }
 105
 106   bool is_unchecked() const { return v == kUncheckedShadow; }
 107
 108   CFICheckFn get_cfi_check() const {
 109     assert(!is_invalid() && !is_unchecked());
 110     uptr aligned_addr = addr & ~(kShadowAlign - 1);
 111     uptr p = aligned_addr - (((uptr)v - 1) << kShadowGranularity);
 112     return reinterpret_cast<CFICheckFn>(p);
 113   }
 114
 115   // Load a shadow value for the given application memory address.
 116   static const ShadowValue load(uptr addr) {
 117     uptr shadow_base = GetShadow();
 118     uptr shadow_offset = MemToShadowOffset(addr);
 119     if (shadow_offset > GetShadowSize())
 120       return ShadowValue(addr, kInvalidShadow);
 121     else
 122       return ShadowValue(
 123           addr, *reinterpret_cast<uint16_t *>(shadow_base + shadow_offset));
 124   }
 125 };
 126
 127 class ShadowBuilder {
 128   uptr shadow_;
 129
 130 public:
 131   // Allocate a new empty shadow (for the entire address space) on the side.
 132   void Start();
 133   // Mark the given address range as unchecked.
 134   // This is used for uninstrumented libraries like libc.
 135   // Any CFI check with a target in that range will pass.
 136   void AddUnchecked(uptr begin, uptr end);
 137   // Mark the given address range as belonging to a library with the given
 138   // cfi_check function.
 139   void Add(uptr begin, uptr end, uptr cfi_check);
 140   // Finish shadow construction. Atomically switch the current active shadow
 141   // region with the newly constructed one and deallocate the former.
 142   void Install();
 143 };
 144
 145 void ShadowBuilder::Start() {
 146   shadow_ = (uptr)MmapNoReserveOrDie(GetShadowSize(), "CFI shadow");
 147   VReport(1, "CFI: shadow at %zx .. %zx\n", shadow_, shadow_ + GetShadowSize());
 148 }
 149
 150 void ShadowBuilder::AddUnchecked(uptr begin, uptr end) {
 151   uint16_t *shadow_begin = MemToShadow(begin, shadow_);
 152   uint16_t *shadow_end = MemToShadow(end - 1, shadow_) + 1;
 153   // memset takes a byte, so our unchecked shadow value requires both bytes to
 154   // be the same. Make sure we're ok during compilation.
 155   static_assert((kUncheckedShadow & 0xff) == ((kUncheckedShadow >> 8) & 0xff),
 156                 "Both bytes of the 16-bit value must be the same!");
 157   memset(shadow_begin, kUncheckedShadow & 0xff,
 158          (shadow_end - shadow_begin) * sizeof(*shadow_begin));
 159 }
 160
 161 void ShadowBuilder::Add(uptr begin, uptr end, uptr cfi_check) {
 162   assert((cfi_check & (kShadowAlign - 1)) == 0);
 163
 164   // Don't fill anything below cfi_check. We can not represent those addresses
 165   // in the shadow, and must make sure at codegen to place all valid call
 166   // targets above cfi_check.
 167   begin = Max(begin, cfi_check);
 168   uint16_t *s = MemToShadow(begin, shadow_);
 169   uint16_t *s_end = MemToShadow(end - 1, shadow_) + 1;
 170   uint16_t sv = ((begin - cfi_check) >> kShadowGranularity) + 1;
 171   for (; s < s_end; s++, sv++)
 172     *s = sv;
 173 }
 174
 175 #if SANITIZER_LINUX || SANITIZER_FREEBSD || SANITIZER_NETBSD
 176 void ShadowBuilder::Install() {
 177   MprotectReadOnly(shadow_, GetShadowSize());
 178   uptr main_shadow = GetShadow();
 179   if (main_shadow) {
 180     // Update.
 181 #if SANITIZER_LINUX
 182     void *res = mremap((void *)shadow_, GetShadowSize(), GetShadowSize(),
 183                        MREMAP_MAYMOVE | MREMAP_FIXED, (void *)main_shadow);
 184     CHECK(res != MAP_FAILED);
 185 #elif SANITIZER_NETBSD
 186     void *res = mremap((void *)shadow_, GetShadowSize(), (void *)main_shadow,
 187                        GetShadowSize(), MAP_FIXED);
 188     CHECK(res != MAP_FAILED);
 189 #else
 190     void *res = MmapFixedOrDie(shadow_, GetShadowSize());
 191     CHECK(res != MAP_FAILED);
 192     ::memcpy(&shadow_, &main_shadow, GetShadowSize());
 193 #endif
 194   } else {
 195     // Initial setup.
 196     CHECK_EQ(kCfiShadowLimitsStorageSize, GetPageSizeCached());
 197     CHECK_EQ(0, GetShadow());
 198     cfi_shadow_limits_storage.limits.start = shadow_;
 199     MprotectReadOnly((uptr)&cfi_shadow_limits_storage,
 200                      sizeof(cfi_shadow_limits_storage));
 201     CHECK_EQ(shadow_, GetShadow());
 202   }
 203 }
 204 #else
 205 #error not implemented
 206 #endif
 207
 208 // This is a workaround for a glibc bug:
 209 // https://sourceware.org/bugzilla/show_bug.cgi?id=15199
 210 // Other platforms can, hopefully, just do
 211 //    dlopen(RTLD_NOLOAD | RTLD_LAZY)
 212 //    dlsym("__cfi_check").
 213 uptr find_cfi_check_in_dso(dl_phdr_info *info) {
 214   const Elf_Dyn *dynamic = nullptr;
 215   for (int i = 0; i < info->dlpi_phnum; ++i) {
 216     if (info->dlpi_phdr[i].p_type == PT_DYNAMIC) {
 217       dynamic =
 218           (const Elf_Dyn *)(info->dlpi_addr + info->dlpi_phdr[i].p_vaddr);
 219       break;
 220     }
 221   }
 222   if (!dynamic) return 0;
 223   uptr strtab = 0, symtab = 0, strsz = 0;
 224   for (const Elf_Dyn *p = dynamic; p->d_tag != PT_NULL; ++p) {
 225     if (p->d_tag == DT_SYMTAB)
 226       symtab = p->d_un.d_ptr;
 227     else if (p->d_tag == DT_STRTAB)
 228       strtab = p->d_un.d_ptr;
 229     else if (p->d_tag == DT_STRSZ)
 230       strsz = p->d_un.d_ptr;
 231   }
 232
 233   if (symtab > strtab) {
 234     VReport(1, "Can not handle: symtab > strtab (%p > %zx)\n", symtab, strtab);
 235     return 0;
 236   }
 237
 238   // Verify that strtab and symtab are inside of the same LOAD segment.
 239   // This excludes VDSO, which has (very high) bogus strtab and symtab pointers.
 240   int phdr_idx;
 241   for (phdr_idx = 0; phdr_idx < info->dlpi_phnum; phdr_idx++) {
 242     const Elf_Phdr *phdr = &info->dlpi_phdr[phdr_idx];
 243     if (phdr->p_type == PT_LOAD) {
 244       uptr beg = info->dlpi_addr + phdr->p_vaddr;
 245       uptr end = beg + phdr->p_memsz;
 246       if (strtab >= beg && strtab + strsz < end && symtab >= beg &&
 247           symtab < end)
 248         break;
 249     }
 250   }
 251   if (phdr_idx == info->dlpi_phnum) {
 252     // Nope, either different segments or just bogus pointers.
 253     // Can not handle this.
 254     VReport(1, "Can not handle: symtab %p, strtab %zx\n", symtab, strtab);
 255     return 0;
 256   }
 257
 258   for (const Elf_Sym *p = (const Elf_Sym *)symtab; (Elf_Addr)p < strtab;
 259        ++p) {
 260     // There is no reliable way to find the end of the symbol table. In
 261     // lld-produces files, there are other sections between symtab and strtab.
 262     // Stop looking when the symbol name is not inside strtab.
 263     if (p->st_name >= strsz) break;
 264     char *name = (char*)(strtab + p->st_name);
 265     if (strcmp(name, "__cfi_check") == 0) {
 266       assert(p->st_info == ELF32_ST_INFO(STB_GLOBAL, STT_FUNC) ||
 267              p->st_info == ELF32_ST_INFO(STB_WEAK, STT_FUNC));
 268       uptr addr = info->dlpi_addr + p->st_value;
 269       return addr;
 270     }
 271   }
 272   return 0;
 273 }
 274
 275 int dl_iterate_phdr_cb(dl_phdr_info *info, size_t size, void *data) {
 276   uptr cfi_check = find_cfi_check_in_dso(info);
 277   if (cfi_check)
 278     VReport(1, "Module '%s' __cfi_check %zx\n", info->dlpi_name, cfi_check);
 279
 280   ShadowBuilder *b = reinterpret_cast<ShadowBuilder *>(data);
 281
 282   for (int i = 0; i < info->dlpi_phnum; i++) {
 283     const Elf_Phdr *phdr = &info->dlpi_phdr[i];
 284     if (phdr->p_type == PT_LOAD) {
 285       // Jump tables are in the executable segment.
 286       // VTables are in the non-executable one.
 287       // Need to fill shadow for both.
 288       // FIXME: reject writable if vtables are in the r/o segment. Depend on
 289       // PT_RELRO?
 290       uptr cur_beg = info->dlpi_addr + phdr->p_vaddr;
 291       uptr cur_end = cur_beg + phdr->p_memsz;
 292       if (cfi_check) {
 293         VReport(1, "   %zx .. %zx\n", cur_beg, cur_end);
 294         b->Add(cur_beg, cur_end, cfi_check);
 295       } else {
 296         b->AddUnchecked(cur_beg, cur_end);
 297       }
 298     }
 299   }
 300   return 0;
 301 }
 302
 303 // Init or update shadow for the current set of loaded libraries.
 304 void UpdateShadow() {
 305   ShadowBuilder b;
 306   b.Start();
 307   dl_iterate_phdr(dl_iterate_phdr_cb, &b);
 308   b.Install();
 309 }
 310
 311 void InitShadow() {
 312   CHECK_EQ(0, GetShadow());
 313   CHECK_EQ(0, GetShadowSize());
 314
 315   uptr vma = GetMaxUserVirtualAddress();
 316   // Shadow is 2 -> 2**kShadowGranularity.
 317   SetShadowSize((vma >> (kShadowGranularity - 1)) + 1);
 318   VReport(1, "CFI: VMA size %zx, shadow size %zx\n", vma, GetShadowSize());
 319
 320   UpdateShadow();
 321 }
 322
 323 THREADLOCAL int in_loader;
 324 BlockingMutex shadow_update_lock(LINKER_INITIALIZED);
 325
 326 void EnterLoader() {
 327   if (in_loader == 0) {
 328     shadow_update_lock.Lock();
 329   }
 330   ++in_loader;
 331 }
 332
 333 void ExitLoader() {
 334   CHECK(in_loader > 0);
 335   --in_loader;
 336   UpdateShadow();
 337   if (in_loader == 0) {
 338     shadow_update_lock.Unlock();
 339   }
 340 }
 341
 342 ALWAYS_INLINE void CfiSlowPathCommon(u64 CallSiteTypeId, void *Ptr,
 343                                      void *DiagData) {
 344   uptr Addr = (uptr)Ptr;
 345   VReport(3, "__cfi_slowpath: %llx, %p\n", CallSiteTypeId, Ptr);
 346   ShadowValue sv = ShadowValue::load(Addr);
 347   if (sv.is_invalid()) {
 348     VReport(1, "CFI: invalid memory region for a check target: %p\n", Ptr);
 349 #ifdef CFI_ENABLE_DIAG
 350     if (DiagData) {
 351       __ubsan_handle_cfi_check_fail(
 352           reinterpret_cast<__ubsan::CFICheckFailData *>(DiagData), Addr, false);
 353       return;
 354     }
 355 #endif
 356     Trap();
 357   }
 358   if (sv.is_unchecked()) {
 359     VReport(2, "CFI: unchecked call (shadow=FFFF): %p\n", Ptr);
 360     return;
 361   }
 362   CFICheckFn cfi_check = sv.get_cfi_check();
 363   VReport(2, "__cfi_check at %p\n", cfi_check);
 364   cfi_check(CallSiteTypeId, Ptr, DiagData);
 365 }
 366
 367 void InitializeFlags() {
 368   SetCommonFlagsDefaults();
 369 #ifdef CFI_ENABLE_DIAG
 370   __ubsan::Flags *uf = __ubsan::flags();
 371   uf->SetDefaults();
 372 #endif
 373
 374   FlagParser cfi_parser;
 375   RegisterCommonFlags(&cfi_parser);
 376   cfi_parser.ParseString(GetEnv("CFI_OPTIONS"));
 377
 378 #ifdef CFI_ENABLE_DIAG
 379   FlagParser ubsan_parser;
 380   __ubsan::RegisterUbsanFlags(&ubsan_parser, uf);
 381   RegisterCommonFlags(&ubsan_parser);
 382
 383   const char *ubsan_default_options = __ubsan::MaybeCallUbsanDefaultOptions();
 384   ubsan_parser.ParseString(ubsan_default_options);
 385   ubsan_parser.ParseString(GetEnv("UBSAN_OPTIONS"));
 386 #endif
 387
 388   InitializeCommonFlags();
 389
 390   if (Verbosity())
 391     ReportUnrecognizedFlags();
 392
 393   if (common_flags()->help) {
 394     cfi_parser.PrintFlagDescriptions();
 395   }
 396 }
 397
 398 } // namespace __cfi
 399
 400 using namespace __cfi;
 401
 402 extern "C" SANITIZER_INTERFACE_ATTRIBUTE void
 403 __cfi_slowpath(u64 CallSiteTypeId, void *Ptr) {
 404   CfiSlowPathCommon(CallSiteTypeId, Ptr, nullptr);
 405 }
 406
 407 #ifdef CFI_ENABLE_DIAG
 408 extern "C" SANITIZER_INTERFACE_ATTRIBUTE void
 409 __cfi_slowpath_diag(u64 CallSiteTypeId, void *Ptr, void *DiagData) {
 410   CfiSlowPathCommon(CallSiteTypeId, Ptr, DiagData);
 411 }
 412 #endif
 413
 414 static void EnsureInterceptorsInitialized();
 415
 416 // Setup shadow for dlopen()ed libraries.
 417 // The actual shadow setup happens after dlopen() returns, which means that
 418 // a library can not be a target of any CFI checks while its constructors are
 419 // running. It's unclear how to fix this without some extra help from libc.
 420 // In glibc, mmap inside dlopen is not interceptable.
 421 // Maybe a seccomp-bpf filter?
 422 // We could insert a high-priority constructor into the library, but that would
 423 // not help with the uninstrumented libraries.
 424 INTERCEPTOR(void*, dlopen, const char *filename, int flag) {
 425   EnsureInterceptorsInitialized();
 426   EnterLoader();
 427   void *handle = REAL(dlopen)(filename, flag);
 428   ExitLoader();
 429   return handle;
 430 }
 431
 432 INTERCEPTOR(int, dlclose, void *handle) {
 433   EnsureInterceptorsInitialized();
 434   EnterLoader();
 435   int res = REAL(dlclose)(handle);
 436   ExitLoader();
 437   return res;
 438 }
 439
 440 static BlockingMutex interceptor_init_lock(LINKER_INITIALIZED);
 441 static bool interceptors_inited = false;
 442
 443 static void EnsureInterceptorsInitialized() {
 444   BlockingMutexLock lock(&interceptor_init_lock);
 445   if (interceptors_inited)
 446     return;
 447
 448   INTERCEPT_FUNCTION(dlopen);
 449   INTERCEPT_FUNCTION(dlclose);
 450
 451   interceptors_inited = true;
 452 }
 453
 454 extern "C" SANITIZER_INTERFACE_ATTRIBUTE
 455 #if !SANITIZER_CAN_USE_PREINIT_ARRAY
 456 // On ELF platforms, the constructor is invoked using .preinit_array (see below)
 457 __attribute__((constructor(0)))
 458 #endif
 459 void __cfi_init() {
 460   SanitizerToolName = "CFI";
 461   InitializeFlags();
 462   InitShadow();
 463
 464 #ifdef CFI_ENABLE_DIAG
 465   __ubsan::InitAsPlugin();
 466 #endif
 467 }
 468
 469 #if SANITIZER_CAN_USE_PREINIT_ARRAY
 470 // On ELF platforms, run cfi initialization before any other constructors.
 471 // On other platforms we use the constructor attribute to arrange to run our
 472 // initialization early.
 473 extern "C" {
 474 __attribute__((section(".preinit_array"),
 475                used)) void (*__cfi_preinit)(void) = __cfi_init;
 476 }
 477 #endif