libexec/rtld-elf/map_object.c

/*-
 * 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.
 *
 * $FreeBSD: stable/10/libexec/rtld-elf/map_object.c 290099 2015-10-28 11:32:39Z kib $
 */

#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 *);
static int convert_prot(int);	/* Elf flags -> mmap protection */
static int convert_flags(int); /* Elf flags -> mmap flags */

/*
 * 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)
{
    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 relro_page;
    size_t relro_size;
    Elf_Addr note_start;
    Elf_Addr note_end;
    char *note_map;
    size_t note_map_len;

    hdr = get_elf_header(fd, path);
    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.
     */
    phdr = (Elf_Phdr *) ((char *)hdr + hdr->e_phoff);
    phsize  = hdr->e_phnum * sizeof (phdr[0]);
    phlimit = phdr + hdr->e_phnum;
    nsegs = -1;
    phdyn = phinterp = phtls = NULL;
    phdr_vaddr = 0;
    relro_page = 0;
    relro_size = 0;
    note_start = 0;
    note_end = 0;
    note_map = NULL;
    segs = alloca(sizeof(segs[0]) * hdr->e_phnum);
    stack_flags = RTLD_DEFAULT_STACK_PF_EXEC | PF_R | PF_W;
    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;
	    }
	    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_GNU_RELRO:
	    relro_page = phdr->p_vaddr;
	    relro_size = phdr->p_memsz;
	    break;

	case PT_NOTE:
	    if (phdr->p_offset > PAGE_SIZE ||
	      phdr->p_offset + phdr->p_filesz > PAGE_SIZE) {
		note_map_len = round_page(phdr->p_offset +
		  phdr->p_filesz) - trunc_page(phdr->p_offset);
		note_map = mmap(NULL, note_map_len, PROT_READ,
		  MAP_PRIVATE, fd, 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 -
		  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 = trunc_page(segs[0]->p_vaddr);
    base_vlimit = round_page(segs[nsegs]->p_vaddr + segs[nsegs]->p_memsz);
    mapsize = base_vlimit - base_vaddr;
    base_addr = (caddr_t) base_vaddr;
    base_flags = MAP_PRIVATE | MAP_ANON | MAP_NOCORE;
    if (npagesizes > 1 && round_page(segs[0]->p_filesz) >= pagesizes[1])
	base_flags |= MAP_ALIGNED_SUPER;

    mapbase = mmap(base_addr, mapsize, PROT_NONE, base_flags, -1, 0);
    if (mapbase == (caddr_t) -1) {
	_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 = trunc_page(segs[i]->p_offset);
	data_vaddr = trunc_page(segs[i]->p_vaddr);
	data_vlimit = 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 (mmap(data_addr, data_vlimit - data_vaddr, data_prot,
	  data_flags | MAP_PREFAULT_READ, fd, data_offset) == (caddr_t) -1) {
	    _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 + (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 && -1 ==
		     mprotect(clear_page, PAGE_SIZE, data_prot|PROT_WRITE)) {
			_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 = 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) == (caddr_t)-1) {
		    _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->textsize = round_page(segs[0]->p_vaddr + segs[0]->p_memsz) -
      base_vaddr;
    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((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) {
	tls_dtv_generation++;
	obj->tlsindex = ++tls_max_index;
	obj->tlssize = phtls->p_memsz;
	obj->tlsalign = phtls->p_align;
	obj->tlsinitsize = phtls->p_filesz;
	obj->tlsinit = mapbase + phtls->p_vaddr;
    }
    obj->stack_flags = stack_flags;
    obj->relro_page = obj->relocbase + trunc_page(relro_page);
    obj->relro_size = round_page(relro_size);
    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);
    munmap(hdr, PAGE_SIZE);
    return (NULL);
}

static Elf_Ehdr *
get_elf_header(int fd, const char *path)
{
	Elf_Ehdr *hdr;

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

	/* Make sure the file is valid */
	if (!IS_ELF(*hdr)) {
		_rtld_error("%s: invalid file format", path);
		goto error;
	}
	if (hdr->e_ident[EI_CLASS] != ELF_TARG_CLASS ||
	    hdr->e_ident[EI_DATA] != ELF_TARG_DATA) {
		_rtld_error("%s: unsupported file layout", path);
		goto error;
	}
	if (hdr->e_ident[EI_VERSION] != EV_CURRENT ||
	    hdr->e_version != EV_CURRENT) {
		_rtld_error("%s: unsupported file version", path);
		goto error;
	}
	if (hdr->e_type != ET_EXEC && hdr->e_type != ET_DYN) {
		_rtld_error("%s: unsupported file type", path);
		goto error;
	}
	if (hdr->e_machine != ELF_TARG_MACH) {
		_rtld_error("%s: unsupported machine", 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 (hdr->e_phentsize != sizeof(Elf_Phdr)) {
		_rtld_error(
	    "%s: invalid shared object: e_phentsize != sizeof(Elf_Phdr)", path);
		goto error;
	}
	if (hdr->e_phoff + hdr->e_phnum * sizeof(Elf_Phdr) >
	    (size_t)PAGE_SIZE) {
		_rtld_error("%s: program header too large", path);
		goto error;
	}
	return (hdr);

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

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

    if (obj->tls_done)
	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(obj->rpath);
    if (obj->priv)
	free(obj->priv);
    if (obj->path)
	free(obj->path);
    if (obj->phdr_alloc)
	free((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.
 */
static int
convert_prot(int elfflags)
{
    int prot = 0;
    if (elfflags & PF_R)
	prot |= PROT_READ;
    if (elfflags & PF_W)
	prot |= PROT_WRITE;
    if (elfflags & PF_X)
	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))
	flags |= MAP_NOCORE;
    return flags;
}