1 /* On-demand PLT fixup for shared objects.
2 Copyright (C) 1995-2019 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
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.
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.
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 <https://www.gnu.org/licenses/>. */
19 #define IN_DL_RUNTIME 1 /* This can be tested in dl-machine.h. */
24 #include <sys/param.h>
26 #include <sysdep-cancel.h>
27 #include "dynamic-link.h"
32 #if (!ELF_MACHINE_NO_RELA && !defined ELF_MACHINE_PLT_REL) \
34 # define PLTREL ElfW(Rela)
36 # define PLTREL ElfW(Rel)
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
46 # define reloc_offset reloc_arg
47 # define reloc_index reloc_arg / sizeof (PLTREL)
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
60 attribute_hidden
__attribute ((noinline
)) ARCH_FIXUP_ATTRIBUTE
62 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
63 ELF_MACHINE_RUNTIME_FIXUP_ARGS
,
65 struct link_map
*l
, ElfW(Word
) reloc_arg
)
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
]);
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
);
77 DL_FIXUP_VALUE_TYPE value
;
79 /* Sanity check that we're really looking at a PLT relocation. */
80 assert (ELFW(R_TYPE
)(reloc
->r_info
) == ELF_MACHINE_JMP_SLOT
);
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)
86 const struct r_found_version
*version
= NULL
;
88 if (l
->l_info
[VERSYMIDX (DT_VERSYM
)] != NULL
)
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)
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
)
104 THREAD_GSCOPE_SET_FLAG ();
105 flags
|= DL_LOOKUP_GSCOPE_LOCK
;
108 #ifdef RTLD_ENABLE_FOREIGN_CALL
109 RTLD_ENABLE_FOREIGN_CALL
;
112 result
= _dl_lookup_symbol_x (strtab
+ sym
->st_name
, l
, &sym
, l
->l_scope
,
113 version
, ELF_RTYPE_CLASS_PLT
, flags
, NULL
);
115 /* We are done with the global scope. */
116 if (!RTLD_SINGLE_THREAD_P
)
117 THREAD_GSCOPE_RESET_FLAG ();
119 #ifdef RTLD_FINALIZE_FOREIGN_CALL
120 RTLD_FINALIZE_FOREIGN_CALL
;
123 /* Currently result contains the base load address (or link map)
124 of the object that defines sym. Now add in the symbol
126 value
= DL_FIXUP_MAKE_VALUE (result
,
127 SYMBOL_ADDRESS (result
, sym
, false));
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));
137 /* And now perhaps the relocation addend. */
138 value
= elf_machine_plt_value (l
, reloc
, value
);
141 && __builtin_expect (ELFW(ST_TYPE
) (sym
->st_info
) == STT_GNU_IFUNC
, 0))
142 value
= elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value
));
144 /* Finally, fix up the plt itself. */
145 if (__glibc_unlikely (GLRO(dl_bind_not
)))
148 return elf_machine_fixup_plt (l
, result
, refsym
, sym
, reloc
, rel_addr
, value
);
153 __attribute ((noinline
)) ARCH_FIXUP_ATTRIBUTE
155 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
156 ELF_MACHINE_RUNTIME_FIXUP_ARGS
,
158 struct link_map
*l
, ElfW(Word
) reloc_arg
,
159 ElfW(Addr
) retaddr
, void *regs
, long int *framesizep
)
161 void (*mcount_fct
) (ElfW(Addr
), ElfW(Addr
)) = _dl_mcount
;
163 if (l
->l_reloc_result
== NULL
)
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
174 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
175 # ifndef ELF_MACHINE_RUNTIME_FIXUP_PARAMS
176 # error Please define ELF_MACHINE_RUNTIME_FIXUP_PARAMS.
178 ELF_MACHINE_RUNTIME_FIXUP_PARAMS
,
183 /* This is the address in the array where we store the result of previous
185 struct reloc_result
*reloc_result
= &l
->l_reloc_result
[reloc_index
];
187 /* CONCURRENCY NOTES:
189 Multiple threads may be calling the same PLT sequence and with
190 LD_AUDIT enabled they will be calling into _dl_profile_fixup to
191 update the reloc_result with the result of the lazy resolution.
192 The reloc_result guard variable is reloc_init, and we use
193 acquire/release loads and store to it to ensure that the results of
194 the structure are consistent with the loaded value of the guard.
195 This does not fix all of the data races that occur when two or more
196 threads read reloc_result->reloc_init with a value of zero and read
197 and write to that reloc_result concurrently. The expectation is
198 generally that while this is a data race it works because the
199 threads write the same values. Until the data races are fixed
200 there is a potential for problems to arise from these data races.
201 The reloc result updates should happen in parallel but there should
202 be an atomic RMW which does the final update to the real result
203 entry (see bug 23790).
205 The following code uses reloc_result->init set to 0 to indicate if it is
206 the first time this object is being relocated, otherwise 1 which
207 indicates the object has already been relocated.
209 Reading/Writing from/to reloc_result->reloc_init must not happen
210 before previous writes to reloc_result complete as they could
211 end-up with an incomplete struct. */
212 DL_FIXUP_VALUE_TYPE value
;
213 unsigned int init
= atomic_load_acquire (&reloc_result
->init
);
217 /* This is the first time we have to relocate this object. */
218 const ElfW(Sym
) *const symtab
219 = (const void *) D_PTR (l
, l_info
[DT_SYMTAB
]);
220 const char *strtab
= (const char *) D_PTR (l
, l_info
[DT_STRTAB
]);
222 const PLTREL
*const reloc
223 = (const void *) (D_PTR (l
, l_info
[DT_JMPREL
]) + reloc_offset
);
224 const ElfW(Sym
) *refsym
= &symtab
[ELFW(R_SYM
) (reloc
->r_info
)];
225 const ElfW(Sym
) *defsym
= refsym
;
228 /* Sanity check that we're really looking at a PLT relocation. */
229 assert (ELFW(R_TYPE
)(reloc
->r_info
) == ELF_MACHINE_JMP_SLOT
);
231 /* Look up the target symbol. If the symbol is marked STV_PROTECTED
232 don't look in the global scope. */
233 if (__builtin_expect (ELFW(ST_VISIBILITY
) (refsym
->st_other
), 0) == 0)
235 const struct r_found_version
*version
= NULL
;
237 if (l
->l_info
[VERSYMIDX (DT_VERSYM
)] != NULL
)
239 const ElfW(Half
) *vernum
=
240 (const void *) D_PTR (l
, l_info
[VERSYMIDX (DT_VERSYM
)]);
241 ElfW(Half
) ndx
= vernum
[ELFW(R_SYM
) (reloc
->r_info
)] & 0x7fff;
242 version
= &l
->l_versions
[ndx
];
243 if (version
->hash
== 0)
247 /* We need to keep the scope around so do some locking. This is
248 not necessary for objects which cannot be unloaded or when
249 we are not using any threads (yet). */
250 int flags
= DL_LOOKUP_ADD_DEPENDENCY
;
251 if (!RTLD_SINGLE_THREAD_P
)
253 THREAD_GSCOPE_SET_FLAG ();
254 flags
|= DL_LOOKUP_GSCOPE_LOCK
;
257 result
= _dl_lookup_symbol_x (strtab
+ refsym
->st_name
, l
,
258 &defsym
, l
->l_scope
, version
,
259 ELF_RTYPE_CLASS_PLT
, flags
, NULL
);
261 /* We are done with the global scope. */
262 if (!RTLD_SINGLE_THREAD_P
)
263 THREAD_GSCOPE_RESET_FLAG ();
265 /* Currently result contains the base load address (or link map)
266 of the object that defines sym. Now add in the symbol
268 value
= DL_FIXUP_MAKE_VALUE (result
,
269 SYMBOL_ADDRESS (result
, defsym
, false));
272 && __builtin_expect (ELFW(ST_TYPE
) (defsym
->st_info
)
273 == STT_GNU_IFUNC
, 0))
274 value
= elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value
));
278 /* We already found the symbol. The module (and therefore its load
279 address) is also known. */
280 value
= DL_FIXUP_MAKE_VALUE (l
, SYMBOL_ADDRESS (l
, refsym
, true));
282 if (__builtin_expect (ELFW(ST_TYPE
) (refsym
->st_info
)
283 == STT_GNU_IFUNC
, 0))
284 value
= elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value
));
288 /* And now perhaps the relocation addend. */
289 value
= elf_machine_plt_value (l
, reloc
, value
);
292 /* Auditing checkpoint: we have a new binding. Provide the
293 auditing libraries the possibility to change the value and
294 tell us whether further auditing is wanted. */
295 if (defsym
!= NULL
&& GLRO(dl_naudit
) > 0)
297 reloc_result
->bound
= result
;
298 /* Compute index of the symbol entry in the symbol table of
299 the DSO with the definition. */
300 reloc_result
->boundndx
= (defsym
301 - (ElfW(Sym
) *) D_PTR (result
,
304 /* Determine whether any of the two participating DSOs is
305 interested in auditing. */
306 if ((l
->l_audit_any_plt
| result
->l_audit_any_plt
) != 0)
308 unsigned int flags
= 0;
309 struct audit_ifaces
*afct
= GLRO(dl_audit
);
310 /* Synthesize a symbol record where the st_value field is
312 ElfW(Sym
) sym
= *defsym
;
313 sym
.st_value
= DL_FIXUP_VALUE_ADDR (value
);
315 /* Keep track whether there is any interest in tracing
316 the call in the lower two bits. */
317 assert (DL_NNS
* 2 <= sizeof (reloc_result
->flags
) * 8);
318 assert ((LA_SYMB_NOPLTENTER
| LA_SYMB_NOPLTEXIT
) == 3);
319 reloc_result
->enterexit
= LA_SYMB_NOPLTENTER
| LA_SYMB_NOPLTEXIT
;
321 const char *strtab2
= (const void *) D_PTR (result
,
324 for (unsigned int cnt
= 0; cnt
< GLRO(dl_naudit
); ++cnt
)
326 /* XXX Check whether both DSOs must request action or
328 struct auditstate
*l_state
= link_map_audit_state (l
, cnt
);
329 struct auditstate
*result_state
330 = link_map_audit_state (result
, cnt
);
331 if ((l_state
->bindflags
& LA_FLG_BINDFROM
) != 0
332 && (result_state
->bindflags
& LA_FLG_BINDTO
) != 0)
334 if (afct
->symbind
!= NULL
)
337 = afct
->symbind (&sym
, reloc_result
->boundndx
,
339 &result_state
->cookie
,
341 strtab2
+ defsym
->st_name
);
342 if (new_value
!= (uintptr_t) sym
.st_value
)
344 flags
|= LA_SYMB_ALTVALUE
;
345 sym
.st_value
= new_value
;
349 /* Remember the results for every audit library and
350 store a summary in the first two bits. */
351 reloc_result
->enterexit
352 &= flags
& (LA_SYMB_NOPLTENTER
| LA_SYMB_NOPLTEXIT
);
353 reloc_result
->enterexit
354 |= ((flags
& (LA_SYMB_NOPLTENTER
| LA_SYMB_NOPLTEXIT
))
358 /* If the bind flags say this auditor is not interested,
359 set the bits manually. */
360 reloc_result
->enterexit
361 |= ((LA_SYMB_NOPLTENTER
| LA_SYMB_NOPLTEXIT
)
367 reloc_result
->flags
= flags
;
368 value
= DL_FIXUP_ADDR_VALUE (sym
.st_value
);
371 /* Set all bits since this symbol binding is not interesting. */
372 reloc_result
->enterexit
= (1u << DL_NNS
) - 1;
376 /* Store the result for later runs. */
377 if (__glibc_likely (! GLRO(dl_bind_not
)))
379 reloc_result
->addr
= value
;
380 /* Guarantee all previous writes complete before
381 init is updated. See CONCURRENCY NOTES earlier */
382 atomic_store_release (&reloc_result
->init
, 1);
387 value
= reloc_result
->addr
;
389 /* By default we do not call the pltexit function. */
390 long int framesize
= -1;
394 /* Auditing checkpoint: report the PLT entering and allow the
395 auditors to change the value. */
396 if (GLRO(dl_naudit
) > 0
397 /* Don't do anything if no auditor wants to intercept this call. */
398 && (reloc_result
->enterexit
& LA_SYMB_NOPLTENTER
) == 0)
400 /* Sanity check: DL_FIXUP_VALUE_CODE_ADDR (value) should have been
401 initialized earlier in this function or in another thread. */
402 assert (DL_FIXUP_VALUE_CODE_ADDR (value
) != 0);
403 ElfW(Sym
) *defsym
= ((ElfW(Sym
) *) D_PTR (reloc_result
->bound
,
405 + reloc_result
->boundndx
);
407 /* Set up the sym parameter. */
408 ElfW(Sym
) sym
= *defsym
;
409 sym
.st_value
= DL_FIXUP_VALUE_ADDR (value
);
411 /* Get the symbol name. */
412 const char *strtab
= (const void *) D_PTR (reloc_result
->bound
,
414 const char *symname
= strtab
+ sym
.st_name
;
416 /* Keep track of overwritten addresses. */
417 unsigned int flags
= reloc_result
->flags
;
419 struct audit_ifaces
*afct
= GLRO(dl_audit
);
420 for (unsigned int cnt
= 0; cnt
< GLRO(dl_naudit
); ++cnt
)
422 if (afct
->ARCH_LA_PLTENTER
!= NULL
423 && (reloc_result
->enterexit
424 & (LA_SYMB_NOPLTENTER
<< (2 * (cnt
+ 1)))) == 0)
426 long int new_framesize
= -1;
427 struct auditstate
*l_state
= link_map_audit_state (l
, cnt
);
428 struct auditstate
*bound_state
429 = link_map_audit_state (reloc_result
->bound
, cnt
);
431 = afct
->ARCH_LA_PLTENTER (&sym
, reloc_result
->boundndx
,
433 &bound_state
->cookie
,
434 regs
, &flags
, symname
,
436 if (new_value
!= (uintptr_t) sym
.st_value
)
438 flags
|= LA_SYMB_ALTVALUE
;
439 sym
.st_value
= new_value
;
442 /* Remember the results for every audit library and
443 store a summary in the first two bits. */
444 reloc_result
->enterexit
445 |= ((flags
& (LA_SYMB_NOPLTENTER
| LA_SYMB_NOPLTEXIT
))
448 if ((reloc_result
->enterexit
& (LA_SYMB_NOPLTEXIT
450 == 0 && new_framesize
!= -1 && framesize
!= -2)
452 /* If this is the first call providing information,
455 framesize
= new_framesize
;
456 /* If two pltenter calls provide conflicting information,
457 use the larger value. */
458 else if (new_framesize
!= framesize
)
459 framesize
= MAX (new_framesize
, framesize
);
466 value
= DL_FIXUP_ADDR_VALUE (sym
.st_value
);
470 /* Store the frame size information. */
471 *framesizep
= framesize
;
473 (*mcount_fct
) (retaddr
, DL_FIXUP_VALUE_CODE_ADDR (value
));
484 _dl_call_pltexit (struct link_map
*l
, ElfW(Word
) reloc_arg
,
485 const void *inregs
, void *outregs
)
488 /* This is the address in the array where we store the result of previous
490 // XXX Maybe the bound information must be stored on the stack since
491 // XXX with bind_not a new value could have been stored in the meantime.
492 struct reloc_result
*reloc_result
= &l
->l_reloc_result
[reloc_index
];
493 ElfW(Sym
) *defsym
= ((ElfW(Sym
) *) D_PTR (reloc_result
->bound
,
495 + reloc_result
->boundndx
);
497 /* Set up the sym parameter. */
498 ElfW(Sym
) sym
= *defsym
;
499 sym
.st_value
= DL_FIXUP_VALUE_ADDR (reloc_result
->addr
);
501 /* Get the symbol name. */
502 const char *strtab
= (const void *) D_PTR (reloc_result
->bound
,
504 const char *symname
= strtab
+ sym
.st_name
;
506 struct audit_ifaces
*afct
= GLRO(dl_audit
);
507 for (unsigned int cnt
= 0; cnt
< GLRO(dl_naudit
); ++cnt
)
509 if (afct
->ARCH_LA_PLTEXIT
!= NULL
510 && (reloc_result
->enterexit
511 & (LA_SYMB_NOPLTEXIT
>> (2 * cnt
))) == 0)
513 struct auditstate
*l_state
= link_map_audit_state (l
, cnt
);
514 struct auditstate
*bound_state
515 = link_map_audit_state (reloc_result
->bound
, cnt
);
516 afct
->ARCH_LA_PLTEXIT (&sym
, reloc_result
->boundndx
,
517 &l_state
->cookie
, &bound_state
->cookie
,
518 inregs
, outregs
, symname
);