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_flags.h"
16#include "sanitizer_platform_interceptors.h"
17
18namespace __sanitizer {
19#if SANITIZER_INTERCEPT_TLS_GET_ADDR
20
21// The actual parameter that comes to __tls_get_addr
22// is a pointer to a struct with two words in it:
23struct TlsGetAddrParam {
24  uptr dso_id;
25  uptr offset;
26};
27
28// Glibc starting from 2.19 allocates tls using __signal_safe_memalign,
29// which has such header.
30struct Glibc_2_19_tls_header {
31  uptr size;
32  uptr start;
33};
34
35// This must be static TLS
36__attribute__((tls_model("initial-exec")))
37static __thread DTLS dtls;
38
39// Make sure we properly destroy the DTLS objects:
40// this counter should never get too large.
41static atomic_uintptr_t number_of_live_dtls;
42
43static const uptr kDestroyedThread = -1;
44
45static inline void DTLS_Deallocate(DTLS::DTV *dtv, uptr size) {
46  if (!size) return;
47  VReport(2, "__tls_get_addr: DTLS_Deallocate %p %zd\n", dtv, size);
48  UnmapOrDie(dtv, size * sizeof(DTLS::DTV));
49  atomic_fetch_sub(&number_of_live_dtls, 1, memory_order_relaxed);
50}
51
52static inline void DTLS_Resize(uptr new_size) {
53  if (dtls.dtv_size >= new_size) return;
54  new_size = RoundUpToPowerOfTwo(new_size);
55  new_size = Max(new_size, 4096UL / sizeof(DTLS::DTV));
56  DTLS::DTV *new_dtv =
57      (DTLS::DTV *)MmapOrDie(new_size * sizeof(DTLS::DTV), "DTLS_Resize");
58  uptr num_live_dtls =
59      atomic_fetch_add(&number_of_live_dtls, 1, memory_order_relaxed);
60  VReport(2, "__tls_get_addr: DTLS_Resize %p %zd\n", &dtls, num_live_dtls);
61  CHECK_LT(num_live_dtls, 1 << 20);
62  uptr old_dtv_size = dtls.dtv_size;
63  DTLS::DTV *old_dtv = dtls.dtv;
64  if (old_dtv_size)
65    internal_memcpy(new_dtv, dtls.dtv, dtls.dtv_size * sizeof(DTLS::DTV));
66  dtls.dtv = new_dtv;
67  dtls.dtv_size = new_size;
68  if (old_dtv_size)
69    DTLS_Deallocate(old_dtv, old_dtv_size);
70}
71
72void DTLS_Destroy() {
73  if (!common_flags()->intercept_tls_get_addr) return;
74  VReport(2, "__tls_get_addr: DTLS_Destroy %p %zd\n", &dtls, dtls.dtv_size);
75  uptr s = dtls.dtv_size;
76  dtls.dtv_size = kDestroyedThread;  // Do this before unmap for AS-safety.
77  DTLS_Deallocate(dtls.dtv, s);
78}
79
80#if defined(__powerpc64__) || defined(__mips__)
81// This is glibc's TLS_DTV_OFFSET:
82// "Dynamic thread vector pointers point 0x8000 past the start of each
83//  TLS block."
84static const uptr kDtvOffset = 0x8000;
85#else
86static const uptr kDtvOffset = 0;
87#endif
88
89DTLS::DTV *DTLS_on_tls_get_addr(void *arg_void, void *res,
90                                uptr static_tls_begin, uptr static_tls_end) {
91  if (!common_flags()->intercept_tls_get_addr) return 0;
92  TlsGetAddrParam *arg = reinterpret_cast<TlsGetAddrParam *>(arg_void);
93  uptr dso_id = arg->dso_id;
94  if (dtls.dtv_size == kDestroyedThread) return 0;
95  DTLS_Resize(dso_id + 1);
96  if (dtls.dtv[dso_id].beg) return 0;
97  uptr tls_size = 0;
98  uptr tls_beg = reinterpret_cast<uptr>(res) - arg->offset - kDtvOffset;
99  VReport(2, "__tls_get_addr: %p {%p,%p} => %p; tls_beg: %p; sp: %p "
100             "num_live_dtls %zd\n",
101          arg, arg->dso_id, arg->offset, res, tls_beg, &tls_beg,
102          atomic_load(&number_of_live_dtls, memory_order_relaxed));
103  if (dtls.last_memalign_ptr == tls_beg) {
104    tls_size = dtls.last_memalign_size;
105    VReport(2, "__tls_get_addr: glibc <=2.18 suspected; tls={%p,%p}\n",
106        tls_beg, tls_size);
107  } else if (tls_beg >= static_tls_begin && tls_beg < static_tls_end) {
108    // This is the static TLS block which was initialized / unpoisoned at thread
109    // creation.
110    VReport(2, "__tls_get_addr: static tls: %p\n", tls_beg);
111    tls_size = 0;
112  } else if ((tls_beg % 4096) == sizeof(Glibc_2_19_tls_header)) {
113    // We may want to check gnu_get_libc_version().
114    Glibc_2_19_tls_header *header = (Glibc_2_19_tls_header *)tls_beg - 1;
115    tls_size = header->size;
116    tls_beg = header->start;
117    VReport(2, "__tls_get_addr: glibc >=2.19 suspected; tls={%p %p}\n",
118        tls_beg, tls_size);
119  } else {
120    VReport(2, "__tls_get_addr: Can't guess glibc version\n");
121    // This may happen inside the DTOR of main thread, so just ignore it.
122    tls_size = 0;
123  }
124  dtls.dtv[dso_id].beg = tls_beg;
125  dtls.dtv[dso_id].size = tls_size;
126  return dtls.dtv + dso_id;
127}
128
129void DTLS_on_libc_memalign(void *ptr, uptr size) {
130  if (!common_flags()->intercept_tls_get_addr) return;
131  VReport(2, "DTLS_on_libc_memalign: %p %p\n", ptr, size);
132  dtls.last_memalign_ptr = reinterpret_cast<uptr>(ptr);
133  dtls.last_memalign_size = size;
134}
135
136DTLS *DTLS_Get() { return &dtls; }
137
138bool DTLSInDestruction(DTLS *dtls) {
139  return dtls->dtv_size == kDestroyedThread;
140}
141
142#else
143void DTLS_on_libc_memalign(void *ptr, uptr size) {}
144DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res,
145  unsigned long, unsigned long) { return 0; }
146DTLS *DTLS_Get() { return 0; }
147void DTLS_Destroy() {}
148bool DTLSInDestruction(DTLS *dtls) {
149  UNREACHABLE("dtls is unsupported on this platform!");
150}
151
152#endif  // SANITIZER_INTERCEPT_TLS_GET_ADDR
153
154}  // namespace __sanitizer
155