xref: /freebsd/libexec/rtld-elf/map_object.c (revision a18b956b73cee784e5c422d20fd0e4dabebd7eee)
1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause
3  *
4  * Copyright 1996-1998 John D. Polstra.
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  *
16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26  *
27  * $FreeBSD$
28  */
29 
30 #define _WANT_P_OSREL
31 #include <sys/param.h>
32 #include <sys/mman.h>
33 #include <sys/stat.h>
34 
35 #include <errno.h>
36 #include <stddef.h>
37 #include <stdlib.h>
38 #include <string.h>
39 #include <unistd.h>
40 
41 #include "debug.h"
42 #include "rtld.h"
43 
44 static Elf_Ehdr *get_elf_header(int, const char *, const struct stat *,
45     Elf_Phdr **phdr);
46 static int convert_flags(int); /* Elf flags -> mmap flags */
47 
48 int __getosreldate(void);
49 
50 static bool
51 phdr_in_zero_page(const Elf_Ehdr *hdr)
52 {
53 	return (hdr->e_phoff + hdr->e_phnum * sizeof(Elf_Phdr) <= page_size);
54 }
55 
56 /*
57  * Map a shared object into memory.  The "fd" argument is a file descriptor,
58  * which must be open on the object and positioned at its beginning.
59  * The "path" argument is a pathname that is used only for error messages.
60  *
61  * The return value is a pointer to a newly-allocated Obj_Entry structure
62  * for the shared object.  Returns NULL on failure.
63  */
64 Obj_Entry *
65 map_object(int fd, const char *path, const struct stat *sb)
66 {
67     Obj_Entry *obj;
68     Elf_Ehdr *hdr;
69     int i;
70     Elf_Phdr *phdr;
71     Elf_Phdr *phlimit;
72     Elf_Phdr **segs;
73     int nsegs;
74     Elf_Phdr *phdyn;
75     Elf_Phdr *phinterp;
76     Elf_Phdr *phtls;
77     caddr_t mapbase;
78     size_t mapsize;
79     Elf_Addr base_vaddr;
80     Elf_Addr base_vlimit;
81     caddr_t base_addr;
82     int base_flags;
83     Elf_Off data_offset;
84     Elf_Addr data_vaddr;
85     Elf_Addr data_vlimit;
86     caddr_t data_addr;
87     int data_prot;
88     int data_flags;
89     Elf_Addr clear_vaddr;
90     caddr_t clear_addr;
91     caddr_t clear_page;
92     Elf_Addr phdr_vaddr;
93     size_t nclear, phsize;
94     Elf_Addr bss_vaddr;
95     Elf_Addr bss_vlimit;
96     caddr_t bss_addr;
97     Elf_Word stack_flags;
98     Elf_Addr relro_page;
99     size_t relro_size;
100     Elf_Addr note_start;
101     Elf_Addr note_end;
102     char *note_map;
103     size_t note_map_len;
104     Elf_Addr text_end;
105 
106     hdr = get_elf_header(fd, path, sb, &phdr);
107     if (hdr == NULL)
108 	return (NULL);
109 
110     /*
111      * Scan the program header entries, and save key information.
112      * We expect that the loadable segments are ordered by load address.
113      */
114     phsize  = hdr->e_phnum * sizeof(phdr[0]);
115     phlimit = phdr + hdr->e_phnum;
116     nsegs = -1;
117     phdyn = phinterp = phtls = NULL;
118     phdr_vaddr = 0;
119     relro_page = 0;
120     relro_size = 0;
121     note_start = 0;
122     note_end = 0;
123     note_map = NULL;
124     note_map_len = 0;
125     segs = alloca(sizeof(segs[0]) * hdr->e_phnum);
126     stack_flags = PF_X | PF_R | PF_W;
127     text_end = 0;
128     while (phdr < phlimit) {
129 	switch (phdr->p_type) {
130 
131 	case PT_INTERP:
132 	    phinterp = phdr;
133 	    break;
134 
135 	case PT_LOAD:
136 	    segs[++nsegs] = phdr;
137 	    if ((segs[nsegs]->p_align & (page_size - 1)) != 0) {
138 		_rtld_error("%s: PT_LOAD segment %d not page-aligned",
139 		    path, nsegs);
140 		goto error;
141 	    }
142 	    if ((segs[nsegs]->p_flags & PF_X) == PF_X) {
143 		text_end = MAX(text_end,
144 		    rtld_round_page(segs[nsegs]->p_vaddr +
145 		    segs[nsegs]->p_memsz));
146 	    }
147 	    break;
148 
149 	case PT_PHDR:
150 	    phdr_vaddr = phdr->p_vaddr;
151 	    phsize = phdr->p_memsz;
152 	    break;
153 
154 	case PT_DYNAMIC:
155 	    phdyn = phdr;
156 	    break;
157 
158 	case PT_TLS:
159 	    phtls = phdr;
160 	    break;
161 
162 	case PT_GNU_STACK:
163 	    stack_flags = phdr->p_flags;
164 	    break;
165 
166 	case PT_GNU_RELRO:
167 	    relro_page = phdr->p_vaddr;
168 	    relro_size = phdr->p_memsz;
169 	    break;
170 
171 	case PT_NOTE:
172 	    if (phdr->p_offset > page_size ||
173 	      phdr->p_offset + phdr->p_filesz > page_size) {
174 		note_map_len = rtld_round_page(phdr->p_offset +
175 		  phdr->p_filesz) - rtld_trunc_page(phdr->p_offset);
176 		note_map = mmap(NULL, note_map_len, PROT_READ,
177 		  MAP_PRIVATE, fd, rtld_trunc_page(phdr->p_offset));
178 		if (note_map == MAP_FAILED) {
179 		    _rtld_error("%s: error mapping PT_NOTE (%d)", path, errno);
180 		    goto error;
181 		}
182 		note_start = (Elf_Addr)(note_map + phdr->p_offset -
183 		  rtld_trunc_page(phdr->p_offset));
184 	    } else {
185 		note_start = (Elf_Addr)(char *)hdr + phdr->p_offset;
186 	    }
187 	    note_end = note_start + phdr->p_filesz;
188 	    break;
189 	}
190 
191 	++phdr;
192     }
193     if (phdyn == NULL) {
194 	_rtld_error("%s: object is not dynamically-linked", path);
195 	goto error;
196     }
197 
198     if (nsegs < 0) {
199 	_rtld_error("%s: too few PT_LOAD segments", path);
200 	goto error;
201     }
202 
203     /*
204      * Map the entire address space of the object, to stake out our
205      * contiguous region, and to establish the base address for relocation.
206      */
207     base_vaddr = rtld_trunc_page(segs[0]->p_vaddr);
208     base_vlimit = rtld_round_page(segs[nsegs]->p_vaddr + segs[nsegs]->p_memsz);
209     mapsize = base_vlimit - base_vaddr;
210     base_addr = (caddr_t) base_vaddr;
211     base_flags = __getosreldate() >= P_OSREL_MAP_GUARD ? MAP_GUARD :
212 	MAP_PRIVATE | MAP_ANON | MAP_NOCORE;
213     if (npagesizes > 1 && rtld_round_page(segs[0]->p_filesz) >= pagesizes[1])
214 	base_flags |= MAP_ALIGNED_SUPER;
215     if (base_vaddr != 0)
216 	base_flags |= MAP_FIXED | MAP_EXCL;
217 
218     mapbase = mmap(base_addr, mapsize, PROT_NONE, base_flags, -1, 0);
219     if (mapbase == MAP_FAILED) {
220 	_rtld_error("%s: mmap of entire address space failed: %s",
221 	  path, rtld_strerror(errno));
222 	goto error;
223     }
224     if (base_addr != NULL && mapbase != base_addr) {
225 	_rtld_error("%s: mmap returned wrong address: wanted %p, got %p",
226 	  path, base_addr, mapbase);
227 	goto error1;
228     }
229 
230     for (i = 0; i <= nsegs; i++) {
231 	/* Overlay the segment onto the proper region. */
232 	data_offset = rtld_trunc_page(segs[i]->p_offset);
233 	data_vaddr = rtld_trunc_page(segs[i]->p_vaddr);
234 	data_vlimit = rtld_round_page(segs[i]->p_vaddr + segs[i]->p_filesz);
235 	data_addr = mapbase + (data_vaddr - base_vaddr);
236 	data_prot = convert_prot(segs[i]->p_flags);
237 	data_flags = convert_flags(segs[i]->p_flags) | MAP_FIXED;
238 	if (data_vlimit != data_vaddr &&
239 	    mmap(data_addr, data_vlimit - data_vaddr, data_prot,
240 	    data_flags | MAP_PREFAULT_READ, fd, data_offset) == MAP_FAILED) {
241 		_rtld_error("%s: mmap of data failed: %s", path,
242 		    rtld_strerror(errno));
243 		goto error1;
244 	}
245 
246 	/* Do BSS setup */
247 	if (segs[i]->p_filesz != segs[i]->p_memsz) {
248 
249 	    /* Clear any BSS in the last page of the segment. */
250 	    clear_vaddr = segs[i]->p_vaddr + segs[i]->p_filesz;
251 	    clear_addr = mapbase + (clear_vaddr - base_vaddr);
252 	    clear_page = mapbase + (rtld_trunc_page(clear_vaddr) - base_vaddr);
253 
254 	    if ((nclear = data_vlimit - clear_vaddr) > 0) {
255 		/* Make sure the end of the segment is writable */
256 		if ((data_prot & PROT_WRITE) == 0 && -1 ==
257 		     mprotect(clear_page, page_size, data_prot|PROT_WRITE)) {
258 			_rtld_error("%s: mprotect failed: %s", path,
259 			    rtld_strerror(errno));
260 			goto error1;
261 		}
262 
263 		memset(clear_addr, 0, nclear);
264 
265 		/* Reset the data protection back */
266 		if ((data_prot & PROT_WRITE) == 0)
267 		    mprotect(clear_page, page_size, data_prot);
268 	    }
269 
270 	    /* Overlay the BSS segment onto the proper region. */
271 	    bss_vaddr = data_vlimit;
272 	    bss_vlimit = rtld_round_page(segs[i]->p_vaddr + segs[i]->p_memsz);
273 	    bss_addr = mapbase +  (bss_vaddr - base_vaddr);
274 	    if (bss_vlimit > bss_vaddr) {	/* There is something to do */
275 		if (mmap(bss_addr, bss_vlimit - bss_vaddr, data_prot,
276 		    data_flags | MAP_ANON, -1, 0) == MAP_FAILED) {
277 		    _rtld_error("%s: mmap of bss failed: %s", path,
278 			rtld_strerror(errno));
279 		    goto error1;
280 		}
281 	    }
282 	}
283 
284 	if (phdr_vaddr == 0 && data_offset <= hdr->e_phoff &&
285 	  (data_vlimit - data_vaddr + data_offset) >=
286 	  (hdr->e_phoff + hdr->e_phnum * sizeof (Elf_Phdr))) {
287 	    phdr_vaddr = data_vaddr + hdr->e_phoff - data_offset;
288 	}
289     }
290 
291     obj = obj_new();
292     if (sb != NULL) {
293 	obj->dev = sb->st_dev;
294 	obj->ino = sb->st_ino;
295     }
296     obj->mapbase = mapbase;
297     obj->mapsize = mapsize;
298     obj->vaddrbase = base_vaddr;
299     obj->relocbase = mapbase - base_vaddr;
300     obj->dynamic = (const Elf_Dyn *)(obj->relocbase + phdyn->p_vaddr);
301     if (hdr->e_entry != 0)
302 	obj->entry = (caddr_t)(obj->relocbase + hdr->e_entry);
303     if (phdr_vaddr != 0) {
304 	obj->phdr = (const Elf_Phdr *)(obj->relocbase + phdr_vaddr);
305     } else {
306 	obj->phdr = malloc(phsize);
307 	if (obj->phdr == NULL) {
308 	    obj_free(obj);
309 	    _rtld_error("%s: cannot allocate program header", path);
310 	    goto error1;
311 	}
312 	memcpy(__DECONST(char *, obj->phdr), (char *)hdr + hdr->e_phoff, phsize);
313 	obj->phdr_alloc = true;
314     }
315     obj->phsize = phsize;
316     if (phinterp != NULL)
317 	obj->interp = (const char *)(obj->relocbase + phinterp->p_vaddr);
318     if (phtls != NULL) {
319 	tls_dtv_generation++;
320 	obj->tlsindex = ++tls_max_index;
321 	obj->tlssize = phtls->p_memsz;
322 	obj->tlsalign = phtls->p_align;
323 	obj->tlspoffset = phtls->p_offset;
324 	obj->tlsinitsize = phtls->p_filesz;
325 	obj->tlsinit = mapbase + phtls->p_vaddr;
326     }
327     obj->stack_flags = stack_flags;
328     obj->relro_page = obj->relocbase + rtld_trunc_page(relro_page);
329     obj->relro_size = rtld_trunc_page(relro_page + relro_size) -
330       rtld_trunc_page(relro_page);
331     if (note_start < note_end)
332 	digest_notes(obj, note_start, note_end);
333     if (note_map != NULL)
334 	munmap(note_map, note_map_len);
335     munmap(hdr, page_size);
336     return (obj);
337 
338 error1:
339     munmap(mapbase, mapsize);
340 error:
341     if (note_map != NULL && note_map != MAP_FAILED)
342 	munmap(note_map, note_map_len);
343     if (!phdr_in_zero_page(hdr))
344 	munmap(phdr, hdr->e_phnum * sizeof(phdr[0]));
345     munmap(hdr, page_size);
346     return (NULL);
347 }
348 
349 bool
350 check_elf_headers(const Elf_Ehdr *hdr, const char *path)
351 {
352 	if (!IS_ELF(*hdr)) {
353 		_rtld_error("%s: invalid file format", path);
354 		return (false);
355 	}
356 	if (hdr->e_ident[EI_CLASS] != ELF_TARG_CLASS ||
357 	    hdr->e_ident[EI_DATA] != ELF_TARG_DATA) {
358 		_rtld_error("%s: unsupported file layout", path);
359 		return (false);
360 	}
361 	if (hdr->e_ident[EI_VERSION] != EV_CURRENT ||
362 	    hdr->e_version != EV_CURRENT) {
363 		_rtld_error("%s: unsupported file version", path);
364 		return (false);
365 	}
366 	if (hdr->e_type != ET_EXEC && hdr->e_type != ET_DYN) {
367 		_rtld_error("%s: unsupported file type", path);
368 		return (false);
369 	}
370 	if (hdr->e_machine != ELF_TARG_MACH) {
371 		_rtld_error("%s: unsupported machine", path);
372 		return (false);
373 	}
374 	if (hdr->e_phentsize != sizeof(Elf_Phdr)) {
375 		_rtld_error(
376 	    "%s: invalid shared object: e_phentsize != sizeof(Elf_Phdr)", path);
377 		return (false);
378 	}
379 	return (true);
380 }
381 
382 static Elf_Ehdr *
383 get_elf_header(int fd, const char *path, const struct stat *sbp,
384     Elf_Phdr **phdr_p)
385 {
386 	Elf_Ehdr *hdr;
387 	Elf_Phdr *phdr;
388 
389 	/* Make sure file has enough data for the ELF header */
390 	if (sbp != NULL && sbp->st_size < (off_t)sizeof(Elf_Ehdr)) {
391 		_rtld_error("%s: invalid file format", path);
392 		return (NULL);
393 	}
394 
395 	hdr = mmap(NULL, page_size, PROT_READ, MAP_PRIVATE | MAP_PREFAULT_READ,
396 	    fd, 0);
397 	if (hdr == MAP_FAILED) {
398 		_rtld_error("%s: read error: %s", path, rtld_strerror(errno));
399 		return (NULL);
400 	}
401 
402 	/* Make sure the file is valid */
403 	if (!check_elf_headers(hdr, path))
404 		goto error;
405 
406 	/*
407 	 * We rely on the program header being in the first page.  This is
408 	 * not strictly required by the ABI specification, but it seems to
409 	 * always true in practice.  And, it simplifies things considerably.
410 	 */
411 	if (phdr_in_zero_page(hdr)) {
412 		phdr = (Elf_Phdr *)((char *)hdr + hdr->e_phoff);
413 	} else {
414 		phdr = mmap(NULL, hdr->e_phnum * sizeof(phdr[0]),
415 		    PROT_READ, MAP_PRIVATE | MAP_PREFAULT_READ, fd,
416 		    hdr->e_phoff);
417 		if (phdr == MAP_FAILED) {
418 			_rtld_error("%s: error mapping phdr: %s", path,
419 			    rtld_strerror(errno));
420 			goto error;
421 		}
422 	}
423 	*phdr_p = phdr;
424 	return (hdr);
425 
426 error:
427 	munmap(hdr, page_size);
428 	return (NULL);
429 }
430 
431 void
432 obj_free(Obj_Entry *obj)
433 {
434     Objlist_Entry *elm;
435 
436     if (obj->tls_static)
437 	free_tls_offset(obj);
438     while (obj->needed != NULL) {
439 	Needed_Entry *needed = obj->needed;
440 	obj->needed = needed->next;
441 	free(needed);
442     }
443     while (!STAILQ_EMPTY(&obj->names)) {
444 	Name_Entry *entry = STAILQ_FIRST(&obj->names);
445 	STAILQ_REMOVE_HEAD(&obj->names, link);
446 	free(entry);
447     }
448     while (!STAILQ_EMPTY(&obj->dldags)) {
449 	elm = STAILQ_FIRST(&obj->dldags);
450 	STAILQ_REMOVE_HEAD(&obj->dldags, link);
451 	free(elm);
452     }
453     while (!STAILQ_EMPTY(&obj->dagmembers)) {
454 	elm = STAILQ_FIRST(&obj->dagmembers);
455 	STAILQ_REMOVE_HEAD(&obj->dagmembers, link);
456 	free(elm);
457     }
458     if (obj->vertab)
459 	free(obj->vertab);
460     if (obj->origin_path)
461 	free(obj->origin_path);
462     if (obj->z_origin)
463 	free(__DECONST(void*, obj->rpath));
464     if (obj->priv)
465 	free(obj->priv);
466     if (obj->path)
467 	free(obj->path);
468     if (obj->phdr_alloc)
469 	free(__DECONST(void *, obj->phdr));
470     free(obj);
471 }
472 
473 Obj_Entry *
474 obj_new(void)
475 {
476     Obj_Entry *obj;
477 
478     obj = CNEW(Obj_Entry);
479     STAILQ_INIT(&obj->dldags);
480     STAILQ_INIT(&obj->dagmembers);
481     STAILQ_INIT(&obj->names);
482     return obj;
483 }
484 
485 /*
486  * Given a set of ELF protection flags, return the corresponding protection
487  * flags for MMAP.
488  */
489 int
490 convert_prot(int elfflags)
491 {
492     int prot = 0;
493     if (elfflags & PF_R)
494 	prot |= PROT_READ;
495     if (elfflags & PF_W)
496 	prot |= PROT_WRITE;
497     if (elfflags & PF_X)
498 	prot |= PROT_EXEC;
499     return prot;
500 }
501 
502 static int
503 convert_flags(int elfflags)
504 {
505     int flags = MAP_PRIVATE; /* All mappings are private */
506 
507     /*
508      * Readonly mappings are marked "MAP_NOCORE", because they can be
509      * reconstructed by a debugger.
510      */
511     if (!(elfflags & PF_W))
512 	flags |= MAP_NOCORE;
513     return flags;
514 }
515