xref: /llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_tls_get_addr.cpp (revision 6dcd0d4b50ff3da15c316daad9b29633612664f6)
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_allocator_interface.h"
16 #include "sanitizer_atomic.h"
17 #include "sanitizer_common/sanitizer_common.h"
18 #include "sanitizer_common/sanitizer_internal_defs.h"
19 #include "sanitizer_flags.h"
20 #include "sanitizer_platform_interceptors.h"
21 
22 namespace __sanitizer {
23 #if SANITIZER_INTERCEPT_TLS_GET_ADDR
24 
25 // The actual parameter that comes to __tls_get_addr
26 // is a pointer to a struct with two words in it:
27 struct TlsGetAddrParam {
28   uptr dso_id;
29   uptr offset;
30 };
31 
32 // This must be static TLS
33 __attribute__((tls_model("initial-exec")))
34 static __thread DTLS dtls;
35 
36 // Make sure we properly destroy the DTLS objects:
37 // this counter should never get too large.
38 static atomic_uintptr_t number_of_live_dtls;
39 
40 static const uptr kDestroyedThread = -1;
41 
42 static void DTLS_Deallocate(DTLS::DTVBlock *block) {
43   VReport(2, "__tls_get_addr: DTLS_Deallocate %p\n", (void *)block);
44   UnmapOrDie(block, sizeof(DTLS::DTVBlock));
45   atomic_fetch_sub(&number_of_live_dtls, 1, memory_order_relaxed);
46 }
47 
48 static DTLS::DTVBlock *DTLS_NextBlock(atomic_uintptr_t *cur) {
49   uptr v = atomic_load(cur, memory_order_acquire);
50   if (v == kDestroyedThread)
51     return nullptr;
52   DTLS::DTVBlock *next = (DTLS::DTVBlock *)v;
53   if (next)
54     return next;
55   DTLS::DTVBlock *new_dtv =
56       (DTLS::DTVBlock *)MmapOrDie(sizeof(DTLS::DTVBlock), "DTLS_NextBlock");
57   uptr prev = 0;
58   if (!atomic_compare_exchange_strong(cur, &prev, (uptr)new_dtv,
59                                       memory_order_seq_cst)) {
60     UnmapOrDie(new_dtv, sizeof(DTLS::DTVBlock));
61     return (DTLS::DTVBlock *)prev;
62   }
63   uptr num_live_dtls =
64       atomic_fetch_add(&number_of_live_dtls, 1, memory_order_relaxed);
65   VReport(2, "__tls_get_addr: DTLS_NextBlock %p %zd\n", (void *)&dtls,
66           num_live_dtls);
67   return new_dtv;
68 }
69 
70 static DTLS::DTV *DTLS_Find(uptr id) {
71   VReport(3, "__tls_get_addr: DTLS_Find %p %zd\n", (void *)&dtls, id);
72   static constexpr uptr kPerBlock = ARRAY_SIZE(DTLS::DTVBlock::dtvs);
73   DTLS::DTVBlock *cur = DTLS_NextBlock(&dtls.dtv_block);
74   if (!cur)
75     return nullptr;
76   for (; id >= kPerBlock; id -= kPerBlock) cur = DTLS_NextBlock(&cur->next);
77   return cur->dtvs + id;
78 }
79 
80 void DTLS_Destroy() {
81   if (!common_flags()->intercept_tls_get_addr) return;
82   VReport(2, "__tls_get_addr: DTLS_Destroy %p\n", (void *)&dtls);
83   DTLS::DTVBlock *block = (DTLS::DTVBlock *)atomic_exchange(
84       &dtls.dtv_block, kDestroyedThread, memory_order_release);
85   while (block) {
86     DTLS::DTVBlock *next =
87         (DTLS::DTVBlock *)atomic_load(&block->next, memory_order_acquire);
88     DTLS_Deallocate(block);
89     block = next;
90   }
91 }
92 
93 #if defined(__powerpc64__) || defined(__mips__)
94 // This is glibc's TLS_DTV_OFFSET:
95 // "Dynamic thread vector pointers point 0x8000 past the start of each
96 //  TLS block." (sysdeps/<arch>/dl-tls.h)
97 static const uptr kDtvOffset = 0x8000;
98 #elif defined(__riscv)
99 // This is glibc's TLS_DTV_OFFSET:
100 // "Dynamic thread vector pointers point 0x800 past the start of each
101 // TLS block." (sysdeps/riscv/dl-tls.h)
102 static const uptr kDtvOffset = 0x800;
103 #else
104 static const uptr kDtvOffset = 0;
105 #endif
106 
107 extern "C" {
108 SANITIZER_WEAK_ATTRIBUTE
109 uptr __sanitizer_get_allocated_size(const void *p);
110 
111 SANITIZER_WEAK_ATTRIBUTE
112 const void *__sanitizer_get_allocated_begin(const void *p);
113 }
114 
115 SANITIZER_INTERFACE_WEAK_DEF(uptr, __sanitizer_get_dtls_size,
116                              const void *tls_begin) {
117   const void *start = __sanitizer_get_allocated_begin(tls_begin);
118   if (!start)
119     return 0;
120   CHECK_LE(start, tls_begin);
121   uptr tls_size = __sanitizer_get_allocated_size(start);
122   VReport(2, "__tls_get_addr: glibc DTLS suspected; tls={%p,0x%zx}\n",
123           tls_begin, tls_size);
124   uptr offset =
125       (reinterpret_cast<uptr>(tls_begin) - reinterpret_cast<uptr>(start));
126   CHECK_LE(offset, tls_size);
127   return tls_size - offset;
128 }
129 
130 DTLS::DTV *DTLS_on_tls_get_addr(void *arg_void, void *res,
131                                 uptr static_tls_begin, uptr static_tls_end) {
132   if (!common_flags()->intercept_tls_get_addr) return 0;
133   TlsGetAddrParam *arg = reinterpret_cast<TlsGetAddrParam *>(arg_void);
134   uptr dso_id = arg->dso_id;
135   DTLS::DTV *dtv = DTLS_Find(dso_id);
136   if (!dtv || dtv->beg)
137     return nullptr;
138   CHECK_LE(static_tls_begin, static_tls_end);
139   uptr tls_beg = reinterpret_cast<uptr>(res) - arg->offset - kDtvOffset;
140   VReport(2,
141           "__tls_get_addr: %p {0x%zx,0x%zx} => %p; tls_beg: %p; sp: %p "
142           "num_live_dtls %zd\n",
143           (void *)arg, arg->dso_id, arg->offset, res, (void *)tls_beg,
144           (void *)&tls_beg,
145           atomic_load(&number_of_live_dtls, memory_order_relaxed));
146   if (tls_beg >= static_tls_begin && tls_beg < static_tls_end) {
147     // This is the static TLS block which was initialized / unpoisoned at thread
148     // creation.
149     VReport(2, "__tls_get_addr: static tls: %p\n", (void *)tls_beg);
150     dtv->beg = tls_beg;
151     dtv->size = 0;
152     return nullptr;
153   }
154   if (uptr tls_size =
155           __sanitizer_get_dtls_size(reinterpret_cast<void *>(tls_beg))) {
156     dtv->beg = tls_beg;
157     dtv->size = tls_size;
158     return dtv;
159   }
160   VReport(2, "__tls_get_addr: Can't guess glibc version\n");
161   // This may happen inside the DTOR a thread, or async signal handlers before
162   // thread initialization, so just ignore it.
163   //
164   // If the unknown block is dynamic TLS, unlikely we will be able to recognize
165   // it in future, mark it as done with '{tls_beg, 0}'.
166   //
167   // If the block is static TLS, possible reason of failed detection is nullptr
168   // in `static_tls_begin`. Regardless of reasons, the future handling of static
169   // TLS is still '{tls_beg, 0}'.
170   dtv->beg = tls_beg;
171   dtv->size = 0;
172   return nullptr;
173 }
174 
175 DTLS *DTLS_Get() { return &dtls; }
176 
177 bool DTLSInDestruction(DTLS *dtls) {
178   return atomic_load(&dtls->dtv_block, memory_order_relaxed) ==
179          kDestroyedThread;
180 }
181 
182 #else
183 SANITIZER_INTERFACE_WEAK_DEF(uptr, __sanitizer_get_dtls_size, const void *) {
184   return 0;
185 }
186 DTLS::DTV *DTLS_on_tls_get_addr(void *arg, void *res,
187   unsigned long, unsigned long) { return 0; }
188 DTLS *DTLS_Get() { return 0; }
189 void DTLS_Destroy() {}
190 bool DTLSInDestruction(DTLS *dtls) {
191   UNREACHABLE("dtls is unsupported on this platform!");
192 }
193 
194 #endif  // SANITIZER_INTERCEPT_TLS_GET_ADDR
195 
196 }  // namespace __sanitizer
197