libsanitizer/sanitizer_common/sanitizer_tls_get_addr.cpp

   1 //===-- sanitizer_tls_get_addr.cpp ----------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // Handle the __tls_get_addr call.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "sanitizer_tls_get_addr.h"
  14
  15 #include "sanitizer_atomic.h"
  16 #include "sanitizer_flags.h"
  17 #include "sanitizer_platform_interceptors.h"
  18
  19 namespace __sanitizer {
  20 #if SANITIZER_INTERCEPT_TLS_GET_ADDR
  21
  22 // The actual parameter that comes to __tls_get_addr
  23 // is a pointer to a struct with two words in it:
  24 struct TlsGetAddrParam {
  25   uptr dso_id;
  26   uptr offset;
  27 };
  28
  29 // Glibc starting from 2.19 allocates tls using __signal_safe_memalign,
  30 // which has such header.
  31 struct Glibc_2_19_tls_header {
  32   uptr size;
  33   uptr start;
  34 };
  35
  36 // This must be static TLS
  37 __attribute__((tls_model("initial-exec")))
  38 static __thread DTLS dtls;
  39
  40 // Make sure we properly destroy the DTLS objects:
  41 // this counter should never get too large.
  42 static atomic_uintptr_t number_of_live_dtls;
  43
  44 static const uptr kDestroyedThread = -1;
  45
  46 static void DTLS_Deallocate(DTLS::DTVBlock *block) {
  47   VReport(2, "__tls_get_addr: DTLS_Deallocate %p %zd\n", block);
  48   UnmapOrDie(block, sizeof(DTLS::DTVBlock));
  49   atomic_fetch_sub(&number_of_live_dtls, 1, memory_order_relaxed);
  50 }
  51
  52 static DTLS::DTVBlock *DTLS_NextBlock(atomic_uintptr_t *cur) {
  53   uptr v = atomic_load(cur, memory_order_acquire);
  54   if (v == kDestroyedThread)
  55     return nullptr;
  56   DTLS::DTVBlock *next = (DTLS::DTVBlock *)v;
  57   if (next)
  58     return next;
  59   DTLS::DTVBlock *new_dtv =
  60       (DTLS::DTVBlock *)MmapOrDie(sizeof(DTLS::DTVBlock), "DTLS_NextBlock");
  61   uptr prev = 0;
  62   if (!atomic_compare_exchange_strong(cur, &prev, (uptr)new_dtv,
  63                                       memory_order_seq_cst)) {
  64     UnmapOrDie(new_dtv, sizeof(DTLS::DTVBlock));
  65     return (DTLS::DTVBlock *)prev;
  66   }
  67   uptr num_live_dtls =
  68       atomic_fetch_add(&number_of_live_dtls, 1, memory_order_relaxed);
  69   VReport(2, "__tls_get_addr: DTLS_NextBlock %p %zd\n", &dtls, num_live_dtls);
  70   return new_dtv;
  71 }
  72
  73 static DTLS::DTV *DTLS_Find(uptr id) {
  74   VReport(2, "__tls_get_addr: DTLS_Find %p %zd\n", &dtls, id);
  75   static constexpr uptr kPerBlock = ARRAY_SIZE(DTLS::DTVBlock::dtvs);
  76   DTLS::DTVBlock *cur = DTLS_NextBlock(&dtls.dtv_block);
  77   if (!cur)
  78     return nullptr;
  79   for (; id >= kPerBlock; id -= kPerBlock) cur = DTLS_NextBlock(&cur->next);
  80   return cur->dtvs + id;
  81 }
  82
  83 void DTLS_Destroy() {
  84   if (!common_flags()->intercept_tls_get_addr) return;
  85   VReport(2, "__tls_get_addr: DTLS_Destroy %p\n", &dtls);
  86   DTLS::DTVBlock *block = (DTLS::DTVBlock *)atomic_exchange(
  87       &dtls.dtv_block, kDestroyedThread, memory_order_release);
  88   while (block) {
  89     DTLS::DTVBlock *next =
  90         (DTLS::DTVBlock *)atomic_load(&block->next, memory_order_acquire);
  91     DTLS_Deallocate(block);
  92     block = next;
  93   }
  94 }
  95
  96 #if defined(__powerpc64__) || defined(__mips__)
  97 // This is glibc's TLS_DTV_OFFSET:
  98 // "Dynamic thread vector pointers point 0x8000 past the start of each
  99 //  TLS block." (sysdeps/<arch>/dl-tls.h)
 100 static const uptr kDtvOffset = 0x8000;
 101 #elif defined(__riscv)
 102 // This is glibc's TLS_DTV_OFFSET:
 103 // "Dynamic thread vector pointers point 0x800 past the start of each
 104 // TLS block." (sysdeps/riscv/dl-tls.h)
 105 static const uptr kDtvOffset = 0x800;
 106 #else
 107 static const uptr kDtvOffset = 0;
 108 #endif
 109
 110 DTLS::DTV *DTLS_on_tls_get_addr(void *arg_void, void *res,
 111                                 uptr static_tls_begin, uptr static_tls_end) {
 112   if (!common_flags()->intercept_tls_get_addr) return 0;
 113   TlsGetAddrParam *arg = reinterpret_cast<TlsGetAddrParam *>(arg_void);
 114   uptr dso_id = arg->dso_id;
 115   DTLS::DTV *dtv = DTLS_Find(dso_id);
 116   if (!dtv || dtv->beg)
 117     return 0;
 118   uptr tls_size = 0;
 119   uptr tls_beg = reinterpret_cast<uptr>(res) - arg->offset - kDtvOffset;
 120   VReport(2, "__tls_get_addr: %p {%p,%p} => %p; tls_beg: %p; sp: %p "
 121              "num_live_dtls %zd\n",
 122           arg, arg->dso_id, arg->offset, res, tls_beg, &tls_beg,
 123           atomic_load(&number_of_live_dtls, memory_order_relaxed));
 124   if (dtls.last_memalign_ptr == tls_beg) {
 125     tls_size = dtls.last_memalign_size;
 126     VReport(2, "__tls_get_addr: glibc <=2.18 suspected; tls={%p,%p}\n",
 127         tls_beg, tls_size);
 128   } else if (tls_beg >= static_tls_begin && tls_beg < static_tls_end) {
 129     // This is the static TLS block which was initialized / unpoisoned at thread
 130     // creation.
 131     VReport(2, "__tls_get_addr: static tls: %p\n", tls_beg);
 132     tls_size = 0;
 133   } else if ((tls_beg % 4096) == sizeof(Glibc_2_19_tls_header)) {
 134     // We may want to check gnu_get_libc_version().
 135     Glibc_2_19_tls_header *header = (Glibc_2_19_tls_header *)tls_beg - 1;
 136     tls_size = header->size;
 137     tls_beg = header->start;
 138     VReport(2, "__tls_get_addr: glibc >=2.19 suspected; tls={%p %p}\n",
 139         tls_beg, tls_size);
 140   } else {
 141     VReport(2, "__tls_get_addr: Can't guess glibc version\n");
 142     // This may happen inside the DTOR of main thread, so just ignore it.
 143     tls_size = 0;
 144   }
 145   dtv->beg = tls_beg;
 146   dtv->size = tls_size;
 147   return dtv;
 148 }
 149
 150 void DTLS_on_libc_memalign(void *ptr, uptr size) {
 151   if (!common_flags()->intercept_tls_get_addr) return;
 152   VReport(2, "DTLS_on_libc_memalign: %p %p\n", ptr, size);
 153   dtls.last_memalign_ptr = reinterpret_cast<uptr>(ptr);
 154   dtls.last_memalign_size = size;
 155 }
 156
 157 DTLS *DTLS_Get() { return &dtls; }
 158
 159 bool DTLSInDestruction(DTLS *dtls) {
 160   return atomic_load(&dtls->dtv_block, memory_order_relaxed) ==
 161          kDestroyedThread;
 162 }
 163
 164 #else
 165 void DTLS_on_libc_memalign(void *ptr, uptr size) {}
 166 DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res,
 167   unsigned long, unsigned long) { return 0; }
 168 DTLS *DTLS_Get() { return 0; }
 169 void DTLS_Destroy() {}
 170 bool DTLSInDestruction(DTLS *dtls) {
 171   UNREACHABLE("dtls is unsupported on this platform!");
 172 }
 173
 174 #endif  // SANITIZER_INTERCEPT_TLS_GET_ADDR
 175
 176 }  // namespace __sanitizer