1 //===-------- cfi.cc ------------------------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the runtime support for the cross-DSO CFI.
12 //===----------------------------------------------------------------------===//
17 #include "sanitizer_common/sanitizer_common.h"
19 #include <sys/link_elf.h>
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
37 #define ElfW32_Dyn Elf_Dyn
38 #define ElfW32_Sym Elf_Sym
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"
47 #ifdef CFI_ENABLE_DIAG
48 #include "ubsan/ubsan_handlers.h"
51 using namespace __sanitizer;
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.
60 char space[kCfiShadowLimitsStorageSize];
65 } cfi_shadow_limits_storage
66 __attribute__((aligned(kCfiShadowLimitsStorageSize)));
67 static constexpr uptr kShadowGranularity = 12;
68 static constexpr uptr kShadowAlign = 1UL << kShadowGranularity; // 4096
70 static constexpr uint16_t kInvalidShadow = 0;
71 static constexpr uint16_t kUncheckedShadow = 0xFFFFU;
73 // Get the start address of the CFI shadow region.
75 return cfi_shadow_limits_storage.limits.start;
78 uptr GetShadowSize() {
79 return cfi_shadow_limits_storage.limits.size;
82 // This will only work while the shadow is not allocated.
83 void SetShadowSize(uptr size) {
84 cfi_shadow_limits_storage.limits.size = size;
87 uptr MemToShadowOffset(uptr x) {
88 return (x >> kShadowGranularity) << 1;
91 uint16_t *MemToShadow(uptr x, uptr shadow_base) {
92 return (uint16_t *)(shadow_base + MemToShadowOffset(x));
95 typedef int (*CFICheckFn)(u64, void *, void *);
97 // This class reads and decodes the shadow contents.
101 explicit ShadowValue(uptr addr, uint16_t v) : addr(addr), v(v) {}
104 bool is_invalid() const { return v == kInvalidShadow; }
106 bool is_unchecked() const { return v == kUncheckedShadow; }
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);
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);
123 addr, *reinterpret_cast<uint16_t *>(shadow_base + shadow_offset));
127 class ShadowBuilder {
131 // Allocate a new empty shadow (for the entire address space) on the side.
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.
145 void ShadowBuilder::Start() {
146 shadow_ = (uptr)MmapNoReserveOrDie(GetShadowSize(), "CFI shadow");
147 VReport(1, "CFI: shadow at %zx .. %zx\n", shadow_, shadow_ + GetShadowSize());
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));
161 void ShadowBuilder::Add(uptr begin, uptr end, uptr cfi_check) {
162 assert((cfi_check & (kShadowAlign - 1)) == 0);
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++)
175 #if SANITIZER_LINUX || SANITIZER_FREEBSD || SANITIZER_NETBSD
176 void ShadowBuilder::Install() {
177 MprotectReadOnly(shadow_, GetShadowSize());
178 uptr main_shadow = GetShadow();
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);
190 void *res = MmapFixedOrDie(shadow_, GetShadowSize());
191 CHECK(res != MAP_FAILED);
192 ::memcpy(&shadow_, &main_shadow, GetShadowSize());
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());
205 #error not implemented
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) {
218 (const Elf_Dyn *)(info->dlpi_addr + info->dlpi_phdr[i].p_vaddr);
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;
233 if (symtab > strtab) {
234 VReport(1, "Can not handle: symtab > strtab (%p > %zx)\n", symtab, strtab);
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.
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 &&
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);
258 for (const Elf_Sym *p = (const Elf_Sym *)symtab; (Elf_Addr)p < strtab;
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;
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);
278 VReport(1, "Module '%s' __cfi_check %zx\n", info->dlpi_name, cfi_check);
280 ShadowBuilder *b = reinterpret_cast<ShadowBuilder *>(data);
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
290 uptr cur_beg = info->dlpi_addr + phdr->p_vaddr;
291 uptr cur_end = cur_beg + phdr->p_memsz;
293 VReport(1, " %zx .. %zx\n", cur_beg, cur_end);
294 b->Add(cur_beg, cur_end, cfi_check);
296 b->AddUnchecked(cur_beg, cur_end);
303 // Init or update shadow for the current set of loaded libraries.
304 void UpdateShadow() {
307 dl_iterate_phdr(dl_iterate_phdr_cb, &b);
312 CHECK_EQ(0, GetShadow());
313 CHECK_EQ(0, GetShadowSize());
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());
323 THREADLOCAL int in_loader;
324 BlockingMutex shadow_update_lock(LINKER_INITIALIZED);
327 if (in_loader == 0) {
328 shadow_update_lock.Lock();
334 CHECK(in_loader > 0);
337 if (in_loader == 0) {
338 shadow_update_lock.Unlock();
342 ALWAYS_INLINE void CfiSlowPathCommon(u64 CallSiteTypeId, void *Ptr,
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
351 __ubsan_handle_cfi_check_fail(
352 reinterpret_cast<__ubsan::CFICheckFailData *>(DiagData), Addr, false);
358 if (sv.is_unchecked()) {
359 VReport(2, "CFI: unchecked call (shadow=FFFF): %p\n", Ptr);
362 CFICheckFn cfi_check = sv.get_cfi_check();
363 VReport(2, "__cfi_check at %p\n", cfi_check);
364 cfi_check(CallSiteTypeId, Ptr, DiagData);
367 void InitializeFlags() {
368 SetCommonFlagsDefaults();
369 #ifdef CFI_ENABLE_DIAG
370 __ubsan::Flags *uf = __ubsan::flags();
374 FlagParser cfi_parser;
375 RegisterCommonFlags(&cfi_parser);
376 cfi_parser.ParseString(GetEnv("CFI_OPTIONS"));
378 #ifdef CFI_ENABLE_DIAG
379 FlagParser ubsan_parser;
380 __ubsan::RegisterUbsanFlags(&ubsan_parser, uf);
381 RegisterCommonFlags(&ubsan_parser);
383 const char *ubsan_default_options = __ubsan::MaybeCallUbsanDefaultOptions();
384 ubsan_parser.ParseString(ubsan_default_options);
385 ubsan_parser.ParseString(GetEnv("UBSAN_OPTIONS"));
388 InitializeCommonFlags();
391 ReportUnrecognizedFlags();
393 if (common_flags()->help) {
394 cfi_parser.PrintFlagDescriptions();
400 using namespace __cfi;
402 extern "C" SANITIZER_INTERFACE_ATTRIBUTE void
403 __cfi_slowpath(u64 CallSiteTypeId, void *Ptr) {
404 CfiSlowPathCommon(CallSiteTypeId, Ptr, nullptr);
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);
414 static void EnsureInterceptorsInitialized();
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();
427 void *handle = REAL(dlopen)(filename, flag);
432 INTERCEPTOR(int, dlclose, void *handle) {
433 EnsureInterceptorsInitialized();
435 int res = REAL(dlclose)(handle);
440 static BlockingMutex interceptor_init_lock(LINKER_INITIALIZED);
441 static bool interceptors_inited = false;
443 static void EnsureInterceptorsInitialized() {
444 BlockingMutexLock lock(&interceptor_init_lock);
445 if (interceptors_inited)
448 INTERCEPT_FUNCTION(dlopen);
449 INTERCEPT_FUNCTION(dlclose);
451 interceptors_inited = true;
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)))
460 SanitizerToolName = "CFI";
464 #ifdef CFI_ENABLE_DIAG
465 __ubsan::InitAsPlugin();
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.
474 __attribute__((section(".preinit_array"),
475 used)) void (*__cfi_preinit)(void) = __cfi_init;