1/* On-demand PLT fixup for shared objects.
2 Copyright (C) 1995-2018 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19#define IN_DL_RUNTIME 1 /* This can be tested in dl-machine.h. */
20
21#include <alloca.h>
22#include <stdlib.h>
23#include <unistd.h>
24#include <sys/param.h>
25#include <ldsodefs.h>
26#include <sysdep-cancel.h>
27#include "dynamic-link.h"
28#include <tls.h>
29#include <dl-irel.h>
30
31
32#if (!ELF_MACHINE_NO_RELA && !defined ELF_MACHINE_PLT_REL) \
33 || ELF_MACHINE_NO_REL
34# define PLTREL ElfW(Rela)
35#else
36# define PLTREL ElfW(Rel)
37#endif
38
39/* The fixup functions might have need special attributes. If none
40 are provided define the macro as empty. */
41#ifndef ARCH_FIXUP_ATTRIBUTE
42# define ARCH_FIXUP_ATTRIBUTE
43#endif
44
45#ifndef reloc_offset
46# define reloc_offset reloc_arg
47# define reloc_index reloc_arg / sizeof (PLTREL)
48#endif
49
50
51
52/* This function is called through a special trampoline from the PLT the
53 first time each PLT entry is called. We must perform the relocation
54 specified in the PLT of the given shared object, and return the resolved
55 function address to the trampoline, which will restart the original call
56 to that address. Future calls will bounce directly from the PLT to the
57 function. */
58
59DL_FIXUP_VALUE_TYPE
60attribute_hidden __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
61_dl_fixup (
62# ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
63 ELF_MACHINE_RUNTIME_FIXUP_ARGS,
64# endif
65 struct link_map *l, ElfW(Word) reloc_arg)
66{
67 const ElfW(Sym) *const symtab
68 = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
69 const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
70
71 const PLTREL *const reloc
72 = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
73 const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
74 const ElfW(Sym) *refsym = sym;
75 void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
76 lookup_t result;
77 DL_FIXUP_VALUE_TYPE value;
78
79 /* Sanity check that we're really looking at a PLT relocation. */
80 assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
81
82 /* Look up the target symbol. If the normal lookup rules are not
83 used don't look in the global scope. */
84 if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
85 {
86 const struct r_found_version *version = NULL;
87
88 if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
89 {
90 const ElfW(Half) *vernum =
91 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
92 ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
93 version = &l->l_versions[ndx];
94 if (version->hash == 0)
95 version = NULL;
96 }
97
98 /* We need to keep the scope around so do some locking. This is
99 not necessary for objects which cannot be unloaded or when
100 we are not using any threads (yet). */
101 int flags = DL_LOOKUP_ADD_DEPENDENCY;
102 if (!RTLD_SINGLE_THREAD_P)
103 {
104 THREAD_GSCOPE_SET_FLAG ();
105 flags |= DL_LOOKUP_GSCOPE_LOCK;
106 }
107
108#ifdef RTLD_ENABLE_FOREIGN_CALL
109 RTLD_ENABLE_FOREIGN_CALL;
110#endif
111
112 result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
113 version, ELF_RTYPE_CLASS_PLT, flags, NULL);
114
115 /* We are done with the global scope. */
116 if (!RTLD_SINGLE_THREAD_P)
117 THREAD_GSCOPE_RESET_FLAG ();
118
119#ifdef RTLD_FINALIZE_FOREIGN_CALL
120 RTLD_FINALIZE_FOREIGN_CALL;
121#endif
122
123 /* Currently result contains the base load address (or link map)
124 of the object that defines sym. Now add in the symbol
125 offset. */
126 value = DL_FIXUP_MAKE_VALUE (result,
127 SYMBOL_ADDRESS (result, sym, false));
128 }
129 else
130 {
131 /* We already found the symbol. The module (and therefore its load
132 address) is also known. */
133 value = DL_FIXUP_MAKE_VALUE (l, SYMBOL_ADDRESS (l, sym, true));
134 result = l;
135 }
136
137 /* And now perhaps the relocation addend. */
138 value = elf_machine_plt_value (l, reloc, value);
139
140 if (sym != NULL
141 && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
142 value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
143
144 /* Finally, fix up the plt itself. */
145 if (__glibc_unlikely (GLRO(dl_bind_not)))
146 return value;
147
148 return elf_machine_fixup_plt (l, result, refsym, sym, reloc, rel_addr, value);
149}
150
151#ifndef PROF
152DL_FIXUP_VALUE_TYPE
153__attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
154_dl_profile_fixup (
155#ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
156 ELF_MACHINE_RUNTIME_FIXUP_ARGS,
157#endif
158 struct link_map *l, ElfW(Word) reloc_arg,
159 ElfW(Addr) retaddr, void *regs, long int *framesizep)
160{
161 void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
162
163 if (l->l_reloc_result == NULL)
164 {
165 /* BZ #14843: ELF_DYNAMIC_RELOCATE is called before l_reloc_result
166 is allocated. We will get here if ELF_DYNAMIC_RELOCATE calls a
167 resolver function to resolve an IRELATIVE relocation and that
168 resolver calls a function that is not yet resolved (lazy). For
169 example, the resolver in x86-64 libm.so calls __get_cpu_features
170 defined in libc.so. Skip audit and resolve the external function
171 in this case. */
172 *framesizep = -1;
173 return _dl_fixup (
174# ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
175# ifndef ELF_MACHINE_RUNTIME_FIXUP_PARAMS
176# error Please define ELF_MACHINE_RUNTIME_FIXUP_PARAMS.
177# endif
178 ELF_MACHINE_RUNTIME_FIXUP_PARAMS,
179# endif
180 l, reloc_arg);
181 }
182
183 /* This is the address in the array where we store the result of previous
184 relocations. */
185 struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
186 DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
187
188 DL_FIXUP_VALUE_TYPE value = *resultp;
189 if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
190 {
191 /* This is the first time we have to relocate this object. */
192 const ElfW(Sym) *const symtab
193 = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
194 const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
195
196 const PLTREL *const reloc
197 = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
198 const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
199 const ElfW(Sym) *defsym = refsym;
200 lookup_t result;
201
202 /* Sanity check that we're really looking at a PLT relocation. */
203 assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
204
205 /* Look up the target symbol. If the symbol is marked STV_PROTECTED
206 don't look in the global scope. */
207 if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
208 {
209 const struct r_found_version *version = NULL;
210
211 if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
212 {
213 const ElfW(Half) *vernum =
214 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
215 ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
216 version = &l->l_versions[ndx];
217 if (version->hash == 0)
218 version = NULL;
219 }
220
221 /* We need to keep the scope around so do some locking. This is
222 not necessary for objects which cannot be unloaded or when
223 we are not using any threads (yet). */
224 int flags = DL_LOOKUP_ADD_DEPENDENCY;
225 if (!RTLD_SINGLE_THREAD_P)
226 {
227 THREAD_GSCOPE_SET_FLAG ();
228 flags |= DL_LOOKUP_GSCOPE_LOCK;
229 }
230
231 result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
232 &defsym, l->l_scope, version,
233 ELF_RTYPE_CLASS_PLT, flags, NULL);
234
235 /* We are done with the global scope. */
236 if (!RTLD_SINGLE_THREAD_P)
237 THREAD_GSCOPE_RESET_FLAG ();
238
239 /* Currently result contains the base load address (or link map)
240 of the object that defines sym. Now add in the symbol
241 offset. */
242 value = DL_FIXUP_MAKE_VALUE (result,
243 SYMBOL_ADDRESS (result, defsym, false));
244
245 if (defsym != NULL
246 && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
247 == STT_GNU_IFUNC, 0))
248 value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
249 }
250 else
251 {
252 /* We already found the symbol. The module (and therefore its load
253 address) is also known. */
254 value = DL_FIXUP_MAKE_VALUE (l, SYMBOL_ADDRESS (l, refsym, true));
255
256 if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
257 == STT_GNU_IFUNC, 0))
258 value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
259
260 result = l;
261 }
262 /* And now perhaps the relocation addend. */
263 value = elf_machine_plt_value (l, reloc, value);
264
265#ifdef SHARED
266 /* Auditing checkpoint: we have a new binding. Provide the
267 auditing libraries the possibility to change the value and
268 tell us whether further auditing is wanted. */
269 if (defsym != NULL && GLRO(dl_naudit) > 0)
270 {
271 reloc_result->bound = result;
272 /* Compute index of the symbol entry in the symbol table of
273 the DSO with the definition. */
274 reloc_result->boundndx = (defsym
275 - (ElfW(Sym) *) D_PTR (result,
276 l_info[DT_SYMTAB]));
277
278 /* Determine whether any of the two participating DSOs is
279 interested in auditing. */
280 if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
281 {
282 unsigned int flags = 0;
283 struct audit_ifaces *afct = GLRO(dl_audit);
284 /* Synthesize a symbol record where the st_value field is
285 the result. */
286 ElfW(Sym) sym = *defsym;
287 sym.st_value = DL_FIXUP_VALUE_ADDR (value);
288
289 /* Keep track whether there is any interest in tracing
290 the call in the lower two bits. */
291 assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
292 assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
293 reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
294
295 const char *strtab2 = (const void *) D_PTR (result,
296 l_info[DT_STRTAB]);
297
298 for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
299 {
300 /* XXX Check whether both DSOs must request action or
301 only one */
302 if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
303 && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
304 {
305 if (afct->symbind != NULL)
306 {
307 uintptr_t new_value
308 = afct->symbind (&sym, reloc_result->boundndx,
309 &l->l_audit[cnt].cookie,
310 &result->l_audit[cnt].cookie,
311 &flags,
312 strtab2 + defsym->st_name);
313 if (new_value != (uintptr_t) sym.st_value)
314 {
315 flags |= LA_SYMB_ALTVALUE;
316 sym.st_value = new_value;
317 }
318 }
319
320 /* Remember the results for every audit library and
321 store a summary in the first two bits. */
322 reloc_result->enterexit
323 &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
324 reloc_result->enterexit
325 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
326 << ((cnt + 1) * 2));
327 }
328 else
329 /* If the bind flags say this auditor is not interested,
330 set the bits manually. */
331 reloc_result->enterexit
332 |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
333 << ((cnt + 1) * 2));
334
335 afct = afct->next;
336 }
337
338 reloc_result->flags = flags;
339 value = DL_FIXUP_ADDR_VALUE (sym.st_value);
340 }
341 else
342 /* Set all bits since this symbol binding is not interesting. */
343 reloc_result->enterexit = (1u << DL_NNS) - 1;
344 }
345#endif
346
347 /* Store the result for later runs. */
348 if (__glibc_likely (! GLRO(dl_bind_not)))
349 *resultp = value;
350 }
351
352 /* By default we do not call the pltexit function. */
353 long int framesize = -1;
354
355#ifdef SHARED
356 /* Auditing checkpoint: report the PLT entering and allow the
357 auditors to change the value. */
358 if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
359 /* Don't do anything if no auditor wants to intercept this call. */
360 && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
361 {
362 ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
363 l_info[DT_SYMTAB])
364 + reloc_result->boundndx);
365
366 /* Set up the sym parameter. */
367 ElfW(Sym) sym = *defsym;
368 sym.st_value = DL_FIXUP_VALUE_ADDR (value);
369
370 /* Get the symbol name. */
371 const char *strtab = (const void *) D_PTR (reloc_result->bound,
372 l_info[DT_STRTAB]);
373 const char *symname = strtab + sym.st_name;
374
375 /* Keep track of overwritten addresses. */
376 unsigned int flags = reloc_result->flags;
377
378 struct audit_ifaces *afct = GLRO(dl_audit);
379 for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
380 {
381 if (afct->ARCH_LA_PLTENTER != NULL
382 && (reloc_result->enterexit
383 & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
384 {
385 long int new_framesize = -1;
386 uintptr_t new_value
387 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
388 &l->l_audit[cnt].cookie,
389 &reloc_result->bound->l_audit[cnt].cookie,
390 regs, &flags, symname,
391 &new_framesize);
392 if (new_value != (uintptr_t) sym.st_value)
393 {
394 flags |= LA_SYMB_ALTVALUE;
395 sym.st_value = new_value;
396 }
397
398 /* Remember the results for every audit library and
399 store a summary in the first two bits. */
400 reloc_result->enterexit
401 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
402 << (2 * (cnt + 1)));
403
404 if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
405 << (2 * (cnt + 1))))
406 == 0 && new_framesize != -1 && framesize != -2)
407 {
408 /* If this is the first call providing information,
409 use it. */
410 if (framesize == -1)
411 framesize = new_framesize;
412 /* If two pltenter calls provide conflicting information,
413 use the larger value. */
414 else if (new_framesize != framesize)
415 framesize = MAX (new_framesize, framesize);
416 }
417 }
418
419 afct = afct->next;
420 }
421
422 value = DL_FIXUP_ADDR_VALUE (sym.st_value);
423 }
424#endif
425
426 /* Store the frame size information. */
427 *framesizep = framesize;
428
429 (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
430
431 return value;
432}
433
434#endif /* PROF */
435
436
437#include <stdio.h>
438void
439ARCH_FIXUP_ATTRIBUTE
440_dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
441 const void *inregs, void *outregs)
442{
443#ifdef SHARED
444 /* This is the address in the array where we store the result of previous
445 relocations. */
446 // XXX Maybe the bound information must be stored on the stack since
447 // XXX with bind_not a new value could have been stored in the meantime.
448 struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
449 ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
450 l_info[DT_SYMTAB])
451 + reloc_result->boundndx);
452
453 /* Set up the sym parameter. */
454 ElfW(Sym) sym = *defsym;
455 sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
456
457 /* Get the symbol name. */
458 const char *strtab = (const void *) D_PTR (reloc_result->bound,
459 l_info[DT_STRTAB]);
460 const char *symname = strtab + sym.st_name;
461
462 struct audit_ifaces *afct = GLRO(dl_audit);
463 for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
464 {
465 if (afct->ARCH_LA_PLTEXIT != NULL
466 && (reloc_result->enterexit
467 & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
468 {
469 afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
470 &l->l_audit[cnt].cookie,
471 &reloc_result->bound->l_audit[cnt].cookie,
472 inregs, outregs, symname);
473 }
474
475 afct = afct->next;
476 }
477#endif
478}
479