map_object.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright 1996-1998 John D. Polstra.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/mman.h>
#include <sys/stat.h>

#include <errno.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "debug.h"
#include "rtld.h"

static Elf_Ehdr *get_elf_header(int, const char *, const struct stat *,
    Elf_Phdr **phdr);
static int convert_flags(int); /* Elf flags -> mmap flags */

static bool
phdr_in_zero_page(const Elf_Ehdr *hdr)
{
	return (hdr->e_phoff + hdr->e_phnum * sizeof(Elf_Phdr) <= page_size);
}

/*
 * Map a shared object into memory.  The "fd" argument is a file descriptor,
 * which must be open on the object and positioned at its beginning.
 * The "path" argument is a pathname that is used only for error messages.
 *
 * The return value is a pointer to a newly-allocated Obj_Entry structure
 * for the shared object.  Returns NULL on failure.
 */
Obj_Entry *
map_object(int fd, const char *path, const struct stat *sb, bool ismain)
{
	Obj_Entry *obj;
	Elf_Ehdr *hdr;
	int i;
	Elf_Phdr *phdr;
	Elf_Phdr *phlimit;
	Elf_Phdr **segs;
	int nsegs;
	Elf_Phdr *phdyn;
	Elf_Phdr *phinterp;
	Elf_Phdr *phtls;
	caddr_t mapbase;
	size_t mapsize;
	Elf_Addr base_vaddr;
	Elf_Addr base_vlimit;
	caddr_t base_addr;
	int base_flags;
	Elf_Off data_offset;
	Elf_Addr data_vaddr;
	Elf_Addr data_vlimit;
	caddr_t data_addr;
	int data_prot;
	int data_flags;
	Elf_Addr clear_vaddr;
	caddr_t clear_addr;
	caddr_t clear_page;
	Elf_Addr phdr_vaddr;
	size_t nclear, phsize;
	Elf_Addr bss_vaddr;
	Elf_Addr bss_vlimit;
	caddr_t bss_addr;
	Elf_Word stack_flags;
	Elf_Addr note_start;
	Elf_Addr note_end;
	char *note_map;
	size_t note_map_len;
	Elf_Addr text_end;

	hdr = get_elf_header(fd, path, sb, &phdr);
	if (hdr == NULL)
		return (NULL);

	/*
	 * Scan the program header entries, and save key information.
	 * We expect that the loadable segments are ordered by load address.
	 */
	phsize = hdr->e_phnum * sizeof(phdr[0]);
	phlimit = phdr + hdr->e_phnum;
	nsegs = -1;
	phdyn = phinterp = phtls = NULL;
	phdr_vaddr = 0;
	note_start = 0;
	note_end = 0;
	note_map = NULL;
	note_map_len = 0;
	segs = alloca(sizeof(segs[0]) * hdr->e_phnum);
	stack_flags = PF_X | PF_R | PF_W;
	text_end = 0;
	while (phdr < phlimit) {
		switch (phdr->p_type) {
		case PT_INTERP:
			phinterp = phdr;
			break;

		case PT_LOAD:
			segs[++nsegs] = phdr;
			if ((segs[nsegs]->p_align & (page_size - 1)) != 0) {
				_rtld_error(
				    "%s: PT_LOAD segment %d not page-aligned",
				    path, nsegs);
				goto error;
			}
			if ((segs[nsegs]->p_flags & PF_X) == PF_X) {
				text_end = MAX(text_end,
				    rtld_round_page(segs[nsegs]->p_vaddr +
				    segs[nsegs]->p_memsz));
			}
			break;

		case PT_PHDR:
			phdr_vaddr = phdr->p_vaddr;
			phsize = phdr->p_memsz;
			break;

		case PT_DYNAMIC:
			phdyn = phdr;
			break;

		case PT_TLS:
			phtls = phdr;
			break;

		case PT_GNU_STACK:
			stack_flags = phdr->p_flags;
			break;

		case PT_NOTE:
			if (phdr->p_offset > page_size ||
			    phdr->p_offset + phdr->p_filesz > page_size) {
				note_map_len = rtld_round_page(phdr->p_offset +
				    phdr->p_filesz) -
				    rtld_trunc_page(phdr->p_offset);
				note_map = mmap(NULL, note_map_len, PROT_READ,
				    MAP_PRIVATE, fd,
				    rtld_trunc_page(phdr->p_offset));
				if (note_map == MAP_FAILED) {
					_rtld_error(
					    "%s: error mapping PT_NOTE (%d)",
					    path, errno);
					goto error;
				}
				note_start = (Elf_Addr)(note_map +
				    phdr->p_offset -
				    rtld_trunc_page(phdr->p_offset));
			} else {
				note_start = (Elf_Addr)(char *)hdr +
				    phdr->p_offset;
			}
			note_end = note_start + phdr->p_filesz;
			break;
		}

		++phdr;
	}
	if (phdyn == NULL) {
		_rtld_error("%s: object is not dynamically-linked", path);
		goto error;
	}

	if (nsegs < 0) {
		_rtld_error("%s: too few PT_LOAD segments", path);
		goto error;
	}

	/*
	 * Map the entire address space of the object, to stake out our
	 * contiguous region, and to establish the base address for relocation.
	 */
	base_vaddr = rtld_trunc_page(segs[0]->p_vaddr);
	base_vlimit = rtld_round_page(segs[nsegs]->p_vaddr +
	    segs[nsegs]->p_memsz);
	mapsize = base_vlimit - base_vaddr;
	base_addr = (caddr_t)base_vaddr;
	base_flags = MAP_GUARD;
	if (npagesizes > 1 &&  rtld_round_page(segs[0]->p_filesz) >=
	    pagesizes[1])
		base_flags |= MAP_ALIGNED_SUPER;
	if (base_vaddr != 0)
		base_flags |= MAP_FIXED | MAP_EXCL;

	mapbase = mmap(base_addr, mapsize, PROT_NONE, base_flags, -1, 0);
	if (mapbase == MAP_FAILED) {
		_rtld_error("%s: mmap of entire address space failed: %s",
		    path, rtld_strerror(errno));
		goto error;
	}
	if (base_addr != NULL && mapbase != base_addr) {
		_rtld_error(
		    "%s: mmap returned wrong address: wanted %p, got %p",
		    path, base_addr, mapbase);
		goto error1;
	}

	for (i = 0; i <= nsegs; i++) {
		/* Overlay the segment onto the proper region. */
		data_offset = rtld_trunc_page(segs[i]->p_offset);
		data_vaddr = rtld_trunc_page(segs[i]->p_vaddr);
		data_vlimit = rtld_round_page(segs[i]->p_vaddr +
		    segs[i]->p_filesz);
		data_addr = mapbase + (data_vaddr - base_vaddr);
		data_prot = convert_prot(segs[i]->p_flags);
		data_flags = convert_flags(segs[i]->p_flags) | MAP_FIXED;
		if (data_vlimit != data_vaddr && mmap(data_addr,
		    data_vlimit - data_vaddr, data_prot, data_flags |
		    MAP_PREFAULT_READ, fd, data_offset) == MAP_FAILED) {
			_rtld_error("%s: mmap of data failed: %s",
			    path, rtld_strerror(errno));
			goto error1;
		}

		/* Do BSS setup */
		if (segs[i]->p_filesz != segs[i]->p_memsz) {
			/* Clear any BSS in the last page of the segment. */
			clear_vaddr = segs[i]->p_vaddr + segs[i]->p_filesz;
			clear_addr = mapbase + (clear_vaddr - base_vaddr);
			clear_page = mapbase + (rtld_trunc_page(clear_vaddr) -
			    base_vaddr);

			if ((nclear = data_vlimit - clear_vaddr) > 0) {
				/*
				 * Make sure the end of the segment is
				 * writable.
				 */
				if ((data_prot & PROT_WRITE) == 0 &&
				    mprotect(clear_page, page_size,
				    data_prot | PROT_WRITE) == -1) {
					_rtld_error("%s: mprotect failed: %s",
					    path, rtld_strerror(errno));
					goto error1;
				}

				memset(clear_addr, 0, nclear);

				/* Reset the data protection back */
				if ((data_prot & PROT_WRITE) == 0)
					mprotect(clear_page, page_size,
					    data_prot);
			}

			/* Overlay the BSS segment onto the proper region. */
			bss_vaddr = data_vlimit;
			bss_vlimit = rtld_round_page(segs[i]->p_vaddr +
			    segs[i]->p_memsz);
			bss_addr = mapbase + (bss_vaddr - base_vaddr);
			if (bss_vlimit > bss_vaddr) {
				/* There is something to do */
				if (mmap(bss_addr, bss_vlimit - bss_vaddr,
				    data_prot, data_flags | MAP_ANON, -1,
				    0) == MAP_FAILED) {
					_rtld_error(
					    "%s: mmap of bss failed: %s",
					    path, rtld_strerror(errno));
					goto error1;
				}
			}
		}

		if (phdr_vaddr == 0 && data_offset <= hdr->e_phoff &&
		    data_vlimit - data_vaddr + data_offset >=
		    hdr->e_phoff + hdr->e_phnum * sizeof(Elf_Phdr)) {
			phdr_vaddr = data_vaddr + hdr->e_phoff - data_offset;
		}
	}

	obj = obj_new();
	if (sb != NULL) {
		obj->dev = sb->st_dev;
		obj->ino = sb->st_ino;
	}
	obj->mapbase = mapbase;
	obj->mapsize = mapsize;
	obj->vaddrbase = base_vaddr;
	obj->relocbase = mapbase - base_vaddr;
	obj->dynamic = (const Elf_Dyn *)(obj->relocbase + phdyn->p_vaddr);
	if (hdr->e_entry != 0)
		obj->entry = (caddr_t)(obj->relocbase + hdr->e_entry);
	if (phdr_vaddr != 0) {
		obj->phdr = (const Elf_Phdr *)(obj->relocbase + phdr_vaddr);
	} else {
		obj->phdr = malloc(phsize);
		if (obj->phdr == NULL) {
			obj_free(obj);
			_rtld_error("%s: cannot allocate program header",
			    path);
			goto error1;
		}
		memcpy(__DECONST(char *, obj->phdr), (char *)hdr + hdr->e_phoff,
		    phsize);
		obj->phdr_alloc = true;
	}
	obj->phsize = phsize;
	if (phinterp != NULL)
		obj->interp = (const char *)(obj->relocbase +
		    phinterp->p_vaddr);
	if (phtls != NULL) {
		if (ismain)
			obj->tlsindex = 1;
		else {
			tls_dtv_generation++;
			obj->tlsindex = ++tls_max_index;
		}
		obj->tlssize = phtls->p_memsz;
		obj->tlsalign = phtls->p_align;
		obj->tlspoffset = phtls->p_offset;
		obj->tlsinitsize = phtls->p_filesz;
		obj->tlsinit = obj->relocbase + phtls->p_vaddr;
	}
	obj->stack_flags = stack_flags;
	if (note_start < note_end)
		digest_notes(obj, note_start, note_end);
	if (note_map != NULL)
		munmap(note_map, note_map_len);
	munmap(hdr, page_size);
	return (obj);

error1:
	munmap(mapbase, mapsize);
error:
	if (note_map != NULL && note_map != MAP_FAILED)
		munmap(note_map, note_map_len);
	if (!phdr_in_zero_page(hdr))
		munmap(phdr, hdr->e_phnum * sizeof(phdr[0]));
	munmap(hdr, page_size);
	return (NULL);
}

bool
check_elf_headers(const Elf_Ehdr *hdr, const char *path)
{
	if (!IS_ELF(*hdr)) {
		_rtld_error("%s: invalid file format", path);
		return (false);
	}
	if (hdr->e_ident[EI_CLASS] != ELF_TARG_CLASS ||
	    hdr->e_ident[EI_DATA] != ELF_TARG_DATA) {
		_rtld_error("%s: unsupported file layout", path);
		return (false);
	}
	if (hdr->e_ident[EI_VERSION] != EV_CURRENT ||
	    hdr->e_version != EV_CURRENT) {
		_rtld_error("%s: unsupported file version", path);
		return (false);
	}
	if (hdr->e_type != ET_EXEC && hdr->e_type != ET_DYN) {
		_rtld_error("%s: unsupported file type", path);
		return (false);
	}
	if (hdr->e_machine != ELF_TARG_MACH) {
		_rtld_error("%s: unsupported machine", path);
		return (false);
	}
	if (hdr->e_phentsize != sizeof(Elf_Phdr)) {
		_rtld_error(
	    "%s: invalid shared object: e_phentsize != sizeof(Elf_Phdr)",
		    path);
		return (false);
	}
	return (true);
}

static Elf_Ehdr *
get_elf_header(int fd, const char *path, const struct stat *sbp,
    Elf_Phdr **phdr_p)
{
	Elf_Ehdr *hdr;
	Elf_Phdr *phdr;

	/* Make sure file has enough data for the ELF header */
	if (sbp != NULL && sbp->st_size < (off_t)sizeof(Elf_Ehdr)) {
		_rtld_error("%s: invalid file format", path);
		return (NULL);
	}

	hdr = mmap(NULL, page_size, PROT_READ, MAP_PRIVATE | MAP_PREFAULT_READ,
	    fd, 0);
	if (hdr == MAP_FAILED) {
		_rtld_error("%s: read error: %s", path, rtld_strerror(errno));
		return (NULL);
	}

	/* Make sure the file is valid */
	if (!check_elf_headers(hdr, path))
		goto error;

	/*
	 * We rely on the program header being in the first page.  This is
	 * not strictly required by the ABI specification, but it seems to
	 * always true in practice.  And, it simplifies things considerably.
	 */
	if (phdr_in_zero_page(hdr)) {
		phdr = (Elf_Phdr *)((char *)hdr + hdr->e_phoff);
	} else {
		phdr = mmap(NULL, hdr->e_phnum * sizeof(phdr[0]), PROT_READ,
		    MAP_PRIVATE | MAP_PREFAULT_READ, fd, hdr->e_phoff);
		if (phdr == MAP_FAILED) {
			_rtld_error("%s: error mapping phdr: %s", path,
			    rtld_strerror(errno));
			goto error;
		}
	}
	*phdr_p = phdr;
	return (hdr);

error:
	munmap(hdr, page_size);
	return (NULL);
}

void
obj_free(Obj_Entry *obj)
{
	Objlist_Entry *elm;

	if (obj->tls_static)
		free_tls_offset(obj);
	while (obj->needed != NULL) {
		Needed_Entry *needed = obj->needed;

		obj->needed = needed->next;
		free(needed);
	}
	while (!STAILQ_EMPTY(&obj->names)) {
		Name_Entry *entry = STAILQ_FIRST(&obj->names);

		STAILQ_REMOVE_HEAD(&obj->names, link);
		free(entry);
	}
	while (!STAILQ_EMPTY(&obj->dldags)) {
		elm = STAILQ_FIRST(&obj->dldags);
		STAILQ_REMOVE_HEAD(&obj->dldags, link);
		free(elm);
	}
	while (!STAILQ_EMPTY(&obj->dagmembers)) {
		elm = STAILQ_FIRST(&obj->dagmembers);
		STAILQ_REMOVE_HEAD(&obj->dagmembers, link);
		free(elm);
	}
	if (obj->vertab)
		free(obj->vertab);
	if (obj->origin_path)
		free(obj->origin_path);
	if (obj->z_origin)
		free(__DECONST(void *, obj->rpath));
	if (obj->priv)
		free(obj->priv);
	if (obj->path)
		free(obj->path);
	if (obj->phdr_alloc)
		free(__DECONST(void *, obj->phdr));
	free(obj);
}

Obj_Entry *
obj_new(void)
{
	Obj_Entry *obj;

	obj = CNEW(Obj_Entry);
	STAILQ_INIT(&obj->dldags);
	STAILQ_INIT(&obj->dagmembers);
	STAILQ_INIT(&obj->names);
	return (obj);
}

/*
 * Given a set of ELF protection flags, return the corresponding protection
 * flags for MMAP.
 */
int
convert_prot(int elfflags)
{
	int prot = 0;

	if ((elfflags & PF_R) != 0)
		prot |= PROT_READ;
	if ((elfflags & PF_W) != 0)
		prot |= PROT_WRITE;
	if ((elfflags & PF_X) != 0)
		prot |= PROT_EXEC;
	return (prot);
}

static int
convert_flags(int elfflags)
{
	int flags = MAP_PRIVATE; /* All mappings are private */

	/*
	 * Readonly mappings are marked "MAP_NOCORE", because they can be
	 * reconstructed by a debugger.
	 */
	if ((elfflags & PF_W) == 0)
		flags |= MAP_NOCORE;
	return (flags);
}