xref: /external/elfutils/libdwfl/dwfl_segment_report_module.c

/* Sniff out modules from ELF headers visible in memory segments.
   Copyright (C) 2008-2012 Red Hat, Inc.
   This file is part of elfutils.

   This file is free software; you can redistribute it and/or modify
   it under the terms of either

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at
       your option) any later version

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at
       your option) any later version

   or both in parallel, as here.

   elfutils is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>
#include "../libelf/libelfP.h"	/* For NOTE_ALIGN.  */
#undef	_
#include "libdwflP.h"

#include <elf.h>
#include <gelf.h>
#include <inttypes.h>
#include <sys/param.h>
#include <alloca.h>
#include <endian.h>


/* A good size for the initial read from memory, if it's not too costly.
   This more than covers the phdrs and note segment in the average 64-bit
   binary.  */

#define INITIAL_READ	1024

#if __BYTE_ORDER == __LITTLE_ENDIAN
# define MY_ELFDATA	ELFDATA2LSB
#else
# define MY_ELFDATA	ELFDATA2MSB
#endif


/* Return user segment index closest to ADDR but not above it.
   If NEXT, return the closest to ADDR but not below it.  */
static int
addr_segndx (Dwfl *dwfl, size_t segment, GElf_Addr addr, bool next)
{
  int ndx = -1;
  do
    {
      if (dwfl->lookup_segndx[segment] >= 0)
	ndx = dwfl->lookup_segndx[segment];
      if (++segment >= dwfl->lookup_elts - 1)
	return next ? ndx + 1 : ndx;
    }
  while (dwfl->lookup_addr[segment] < addr);

  if (next)
    {
      while (dwfl->lookup_segndx[segment] < 0)
	if (++segment >= dwfl->lookup_elts - 1)
	  return ndx + 1;
      ndx = dwfl->lookup_segndx[segment];
    }

  return ndx;
}

int
dwfl_segment_report_module (Dwfl *dwfl, int ndx, const char *name,
			    Dwfl_Memory_Callback *memory_callback,
			    void *memory_callback_arg,
			    Dwfl_Module_Callback *read_eagerly,
			    void *read_eagerly_arg)
{
  size_t segment = ndx;

  if (segment >= dwfl->lookup_elts)
    segment = dwfl->lookup_elts - 1;

  while (segment > 0
	 && (dwfl->lookup_segndx[segment] > ndx
	     || dwfl->lookup_segndx[segment] == -1))
    --segment;

  while (dwfl->lookup_segndx[segment] < ndx)
    if (++segment == dwfl->lookup_elts)
      return 0;

  GElf_Addr start = dwfl->lookup_addr[segment];

  inline bool segment_read (int segndx,
			    void **buffer, size_t *buffer_available,
			    GElf_Addr addr, size_t minread)
  {
    return ! (*memory_callback) (dwfl, segndx, buffer, buffer_available,
				 addr, minread, memory_callback_arg);
  }

  inline void release_buffer (void **buffer, size_t *buffer_available)
  {
    if (*buffer != NULL)
      (void) segment_read (-1, buffer, buffer_available, 0, 0);
  }

  /* First read in the file header and check its sanity.  */

  void *buffer = NULL;
  size_t buffer_available = INITIAL_READ;

  inline int finish (void)
  {
    release_buffer (&buffer, &buffer_available);
    return ndx;
  }

  if (segment_read (ndx, &buffer, &buffer_available,
		    start, sizeof (Elf64_Ehdr))
      || memcmp (buffer, ELFMAG, SELFMAG) != 0)
    return finish ();

  inline bool read_portion (void **data, size_t *data_size,
			    GElf_Addr vaddr, size_t filesz)
  {
    if (vaddr - start + filesz > buffer_available
	/* If we're in string mode, then don't consider the buffer we have
	   sufficient unless it contains the terminator of the string.  */
	|| (filesz == 0 && memchr (vaddr - start + buffer, '\0',
				   buffer_available - (vaddr - start)) == NULL))
      {
	*data = NULL;
	*data_size = filesz;
	return segment_read (addr_segndx (dwfl, segment, vaddr, false),
			     data, data_size, vaddr, filesz);
      }

    /* We already have this whole note segment from our initial read.  */
    *data = vaddr - start + buffer;
    *data_size = 0;
    return false;
  }

  inline void finish_portion (void **data, size_t *data_size)
  {
    if (*data_size != 0)
      release_buffer (data, data_size);
  }

  /* Extract the information we need from the file header.  */
  union
  {
    Elf32_Ehdr e32;
    Elf64_Ehdr e64;
  } ehdr;
  GElf_Off phoff;
  uint_fast16_t phnum;
  uint_fast16_t phentsize;
  GElf_Off shdrs_end;
  Elf_Data xlatefrom =
    {
      .d_type = ELF_T_EHDR,
      .d_buf = (void *) buffer,
      .d_version = EV_CURRENT,
    };
  Elf_Data xlateto =
    {
      .d_type = ELF_T_EHDR,
      .d_buf = &ehdr,
      .d_size = sizeof ehdr,
      .d_version = EV_CURRENT,
    };
  switch (((const unsigned char *) buffer)[EI_CLASS])
    {
    case ELFCLASS32:
      xlatefrom.d_size = sizeof (Elf32_Ehdr);
      if (elf32_xlatetom (&xlateto, &xlatefrom,
			  ((const unsigned char *) buffer)[EI_DATA]) == NULL)
	return finish ();
      phoff = ehdr.e32.e_phoff;
      phnum = ehdr.e32.e_phnum;
      phentsize = ehdr.e32.e_phentsize;
      if (phentsize != sizeof (Elf32_Phdr))
	return finish ();
      shdrs_end = ehdr.e32.e_shoff + ehdr.e32.e_shnum * ehdr.e32.e_shentsize;
      break;

    case ELFCLASS64:
      xlatefrom.d_size = sizeof (Elf64_Ehdr);
      if (elf64_xlatetom (&xlateto, &xlatefrom,
			  ((const unsigned char *) buffer)[EI_DATA]) == NULL)
	return finish ();
      phoff = ehdr.e64.e_phoff;
      phnum = ehdr.e64.e_phnum;
      phentsize = ehdr.e64.e_phentsize;
      if (phentsize != sizeof (Elf64_Phdr))
	return finish ();
      shdrs_end = ehdr.e64.e_shoff + ehdr.e64.e_shnum * ehdr.e64.e_shentsize;
      break;

    default:
      return finish ();
    }

  /* The file header tells where to find the program headers.
     These are what we need to find the boundaries of the module.
     Without them, we don't have a module to report.  */

  if (phnum == 0)
    return finish ();

  xlatefrom.d_type = xlateto.d_type = ELF_T_PHDR;
  xlatefrom.d_size = phnum * phentsize;

  void *ph_buffer = NULL;
  size_t ph_buffer_size = 0;
  if (read_portion (&ph_buffer, &ph_buffer_size,
		    start + phoff, xlatefrom.d_size))
    return finish ();

  xlatefrom.d_buf = ph_buffer;

  union
  {
    Elf32_Phdr p32[phnum];
    Elf64_Phdr p64[phnum];
  } phdrs;

  xlateto.d_buf = &phdrs;
  xlateto.d_size = sizeof phdrs;

  /* Track the bounds of the file visible in memory.  */
  GElf_Off file_trimmed_end = 0; /* Proper p_vaddr + p_filesz end.  */
  GElf_Off file_end = 0;	 /* Rounded up to effective page size.  */
  GElf_Off contiguous = 0;	 /* Visible as contiguous file from START.  */
  GElf_Off total_filesz = 0;	 /* Total size of data to read.  */

  /* Collect the bias between START and the containing PT_LOAD's p_vaddr.  */
  GElf_Addr bias = 0;
  bool found_bias = false;

  /* Collect the unbiased bounds of the module here.  */
  GElf_Addr module_start = -1l;
  GElf_Addr module_end = 0;
  GElf_Addr module_address_sync = 0;

  /* If we see PT_DYNAMIC, record it here.  */
  GElf_Addr dyn_vaddr = 0;
  GElf_Xword dyn_filesz = 0;

  /* Collect the build ID bits here.  */
  void *build_id = NULL;
  size_t build_id_len = 0;
  GElf_Addr build_id_vaddr = 0;

  /* Consider a PT_NOTE we've found in the image.  */
  inline void consider_notes (GElf_Addr vaddr, GElf_Xword filesz)
  {
    /* If we have already seen a build ID, we don't care any more.  */
    if (build_id != NULL || filesz == 0)
      return;

    void *data;
    size_t data_size;
    if (read_portion (&data, &data_size, vaddr, filesz))
      return;

    assert (sizeof (Elf32_Nhdr) == sizeof (Elf64_Nhdr));

    void *notes;
    if (ehdr.e32.e_ident[EI_DATA] == MY_ELFDATA)
      notes = data;
    else
      {
	notes = malloc (filesz);
	if (unlikely (notes == NULL))
	  return;
	xlatefrom.d_type = xlateto.d_type = ELF_T_NHDR;
	xlatefrom.d_buf = (void *) data;
	xlatefrom.d_size = filesz;
	xlateto.d_buf = notes;
	xlateto.d_size = filesz;
	if (elf32_xlatetom (&xlateto, &xlatefrom,
			    ehdr.e32.e_ident[EI_DATA]) == NULL)
	  goto done;
      }

    const GElf_Nhdr *nh = notes;
    while ((const void *) nh < (const void *) notes + filesz)
     {
	const void *note_name = nh + 1;
	const void *note_desc = note_name + NOTE_ALIGN (nh->n_namesz);
	if (unlikely ((size_t) ((const void *) notes + filesz
				- note_desc) < nh->n_descsz))
	  break;

	if (nh->n_type == NT_GNU_BUILD_ID
	    && nh->n_descsz > 0
	    && nh->n_namesz == sizeof "GNU"
	    && !memcmp (note_name, "GNU", sizeof "GNU"))
	  {
	    build_id_vaddr = note_desc - (const void *) notes + vaddr;
	    build_id_len = nh->n_descsz;
	    build_id = malloc (nh->n_descsz);
	    if (likely (build_id != NULL))
	      memcpy (build_id, note_desc, build_id_len);
	    break;
	  }

	nh = note_desc + NOTE_ALIGN (nh->n_descsz);
      }

  done:
    if (notes != data)
      free (notes);
    finish_portion (&data, &data_size);
  }

  /* Consider each of the program headers we've read from the image.  */
  inline void consider_phdr (GElf_Word type,
			     GElf_Addr vaddr, GElf_Xword memsz,
			     GElf_Off offset, GElf_Xword filesz,
			     GElf_Xword align)
  {
    switch (type)
      {
      case PT_DYNAMIC:
	dyn_vaddr = vaddr;
	dyn_filesz = filesz;
	break;

      case PT_NOTE:
	/* We calculate from the p_offset of the note segment,
	   because we don't yet know the bias for its p_vaddr.  */
	consider_notes (start + offset, filesz);
	break;

      case PT_LOAD:
	align = dwfl->segment_align > 1 ? dwfl->segment_align : align ?: 1;

	GElf_Addr vaddr_end = (vaddr + memsz + align - 1) & -align;
	GElf_Addr filesz_vaddr = filesz < memsz ? vaddr + filesz : vaddr_end;
	GElf_Off filesz_offset = filesz_vaddr - vaddr + offset;

	if (file_trimmed_end < offset + filesz)
	  {
	    file_trimmed_end = offset + filesz;

	    /* Trim the last segment so we don't bother with zeros
	       in the last page that are off the end of the file.
	       However, if the extra bit in that page includes the
	       section headers, keep them.  */
	    if (shdrs_end <= filesz_offset && shdrs_end > file_trimmed_end)
	      {
		filesz += shdrs_end - file_trimmed_end;
		file_trimmed_end = shdrs_end;
	      }
	  }

	total_filesz += filesz;

	if (file_end < filesz_offset)
	  {
	    file_end = filesz_offset;
	    if (filesz_vaddr - start == filesz_offset)
	      contiguous = file_end;
	  }

	if (!found_bias && (offset & -align) == 0
	    && likely (filesz_offset >= phoff + phnum * phentsize))
	  {
	    bias = start - vaddr;
	    found_bias = true;
	  }

	if ((vaddr & -align) < module_start)
	  {
	    module_start = vaddr & -align;
	    module_address_sync = vaddr + memsz;
	  }

	if (module_end < vaddr_end)
	  module_end = vaddr_end;
	break;
      }
  }
  if (ehdr.e32.e_ident[EI_CLASS] == ELFCLASS32)
    {
      if (elf32_xlatetom (&xlateto, &xlatefrom,
			  ehdr.e32.e_ident[EI_DATA]) == NULL)
	found_bias = false;	/* Trigger error check.  */
      else
	for (uint_fast16_t i = 0; i < phnum; ++i)
	  consider_phdr (phdrs.p32[i].p_type,
			 phdrs.p32[i].p_vaddr, phdrs.p32[i].p_memsz,
			 phdrs.p32[i].p_offset, phdrs.p32[i].p_filesz,
			 phdrs.p32[i].p_align);
    }
  else
    {
      if (elf64_xlatetom (&xlateto, &xlatefrom,
			  ehdr.e32.e_ident[EI_DATA]) == NULL)
	found_bias = false;	/* Trigger error check.  */
      else
	for (uint_fast16_t i = 0; i < phnum; ++i)
	  consider_phdr (phdrs.p64[i].p_type,
			 phdrs.p64[i].p_vaddr, phdrs.p64[i].p_memsz,
			 phdrs.p64[i].p_offset, phdrs.p64[i].p_filesz,
			 phdrs.p64[i].p_align);
    }

  finish_portion (&ph_buffer, &ph_buffer_size);

  /* We must have seen the segment covering offset 0, or else the ELF
     header we read at START was not produced by these program headers.  */
  if (unlikely (!found_bias))
    return finish ();

  /* Now we know enough to report a module for sure: its bounds.  */
  module_start += bias;
  module_end += bias;

  dyn_vaddr += bias;

  /* Our return value now says to skip the segments contained
     within the module.  */
  ndx = addr_segndx (dwfl, segment, module_end, true);

  /* Examine its .dynamic section to get more interesting details.
     If it has DT_SONAME, we'll use that as the module name.
     If it has a DT_DEBUG, then it's actually a PIE rather than a DSO.
     We need its DT_STRTAB and DT_STRSZ to decipher DT_SONAME,
     and they also tell us the essential portion of the file
     for fetching symbols.  */
  GElf_Addr soname_stroff = 0;
  GElf_Addr dynstr_vaddr = 0;
  GElf_Xword dynstrsz = 0;
  bool execlike = false;
  inline bool consider_dyn (GElf_Sxword tag, GElf_Xword val)
  {
    switch (tag)
      {
      default:
	return false;

      case DT_DEBUG:
	execlike = true;
	break;

      case DT_SONAME:
	soname_stroff = val;
	break;

      case DT_STRTAB:
	dynstr_vaddr = val;
	break;

      case DT_STRSZ:
	dynstrsz = val;
	break;
      }

    return soname_stroff != 0 && dynstr_vaddr != 0 && dynstrsz != 0;
  }

  const size_t dyn_entsize = (ehdr.e32.e_ident[EI_CLASS] == ELFCLASS32
			      ? sizeof (Elf32_Dyn) : sizeof (Elf64_Dyn));
  void *dyn_data = NULL;
  size_t dyn_data_size = 0;
  if (dyn_filesz != 0 && dyn_filesz % dyn_entsize == 0
      && ! read_portion (&dyn_data, &dyn_data_size, dyn_vaddr, dyn_filesz))
    {
      union
      {
	Elf32_Dyn d32[dyn_filesz / sizeof (Elf32_Dyn)];
	Elf64_Dyn d64[dyn_filesz / sizeof (Elf64_Dyn)];
      } dyn;

      xlatefrom.d_type = xlateto.d_type = ELF_T_DYN;
      xlatefrom.d_buf = (void *) dyn_data;
      xlatefrom.d_size = dyn_filesz;
      xlateto.d_buf = &dyn;
      xlateto.d_size = sizeof dyn;

      if (ehdr.e32.e_ident[EI_CLASS] == ELFCLASS32)
	{
	  if (elf32_xlatetom (&xlateto, &xlatefrom,
			      ehdr.e32.e_ident[EI_DATA]) != NULL)
	    for (size_t i = 0; i < dyn_filesz / sizeof dyn.d32[0]; ++i)
	      if (consider_dyn (dyn.d32[i].d_tag, dyn.d32[i].d_un.d_val))
		break;
	}
      else
	{
	  if (elf64_xlatetom (&xlateto, &xlatefrom,
			      ehdr.e32.e_ident[EI_DATA]) != NULL)
	    for (size_t i = 0; i < dyn_filesz / sizeof dyn.d64[0]; ++i)
	      if (consider_dyn (dyn.d64[i].d_tag, dyn.d64[i].d_un.d_val))
		break;
	}
    }
  finish_portion (&dyn_data, &dyn_data_size);

  /* We'll use the name passed in or a stupid default if not DT_SONAME.  */
  if (name == NULL)
    name = ehdr.e32.e_type == ET_EXEC ? "[exe]" : execlike ? "[pie]" : "[dso]";

  void *soname = NULL;
  size_t soname_size = 0;
  if (dynstrsz != 0 && dynstr_vaddr != 0)
    {
      /* We know the bounds of the .dynstr section.

	 The DYNSTR_VADDR pointer comes from the .dynamic section
	 (DT_STRTAB, detected above).  Ordinarily the dynamic linker
	 will have adjusted this pointer in place so it's now an
	 absolute address.  But sometimes .dynamic is read-only (in
	 vDSOs and odd architectures), and sometimes the adjustment
	 just hasn't happened yet in the memory image we looked at.
	 So treat DYNSTR_VADDR as an absolute address if it falls
	 within the module bounds, or try applying the phdr bias
	 when that adjusts it to fall within the module bounds.  */

      if ((dynstr_vaddr < module_start || dynstr_vaddr >= module_end)
	  && dynstr_vaddr + bias >= module_start
	  && dynstr_vaddr + bias < module_end)
	dynstr_vaddr += bias;

      if (unlikely (dynstr_vaddr + dynstrsz > module_end))
	dynstrsz = 0;

      /* Try to get the DT_SONAME string.  */
      if (soname_stroff != 0 && soname_stroff + 1 < dynstrsz
	  && ! read_portion (&soname, &soname_size,
			     dynstr_vaddr + soname_stroff, 0))
	name = soname;
    }

  /* Now that we have chosen the module's name and bounds, report it.
     If we found a build ID, report that too.  */

  Dwfl_Module *mod = INTUSE(dwfl_report_module) (dwfl, name,
						 module_start, module_end);
  if (likely (mod != NULL) && build_id != NULL
      && unlikely (INTUSE(dwfl_module_report_build_id) (mod,
							build_id,
							build_id_len,
							build_id_vaddr)))
    {
      mod->gc = true;
      mod = NULL;
    }

  /* At this point we do not need BUILD_ID or NAME any more.
     They have been copied.  */
  free (build_id);
  finish_portion (&soname, &soname_size);

  if (unlikely (mod == NULL))
    {
      ndx = -1;
      return finish ();
    }

  /* We have reported the module.  Now let the caller decide whether we
     should read the whole thing in right now.  */

  const GElf_Off cost = (contiguous < file_trimmed_end ? total_filesz
			 : buffer_available >= contiguous ? 0
			 : contiguous - buffer_available);
  const GElf_Off worthwhile = ((dynstr_vaddr == 0 || dynstrsz == 0) ? 0
			       : dynstr_vaddr + dynstrsz - start);
  const GElf_Off whole = MAX (file_trimmed_end, shdrs_end);

  Elf *elf = NULL;
  if ((*read_eagerly) (MODCB_ARGS (mod), &buffer, &buffer_available,
		       cost, worthwhile, whole, contiguous,
		       read_eagerly_arg, &elf)
      && elf == NULL)
    {
      /* The caller wants to read the whole file in right now, but hasn't
	 done it for us.  Fill in a local image of the virtual file.  */

      void *contents = calloc (1, file_trimmed_end);
      if (unlikely (contents == NULL))
	return finish ();

      inline void final_read (size_t offset, GElf_Addr vaddr, size_t size)
      {
	void *into = contents + offset;
	size_t read_size = size;
	(void) segment_read (addr_segndx (dwfl, segment, vaddr, false),
			     &into, &read_size, vaddr, size);
      }

      if (contiguous < file_trimmed_end)
	{
	  /* We can't use the memory image verbatim as the file image.
	     So we'll be reading into a local image of the virtual file.  */

	  inline void read_phdr (GElf_Word type, GElf_Addr vaddr,
				 GElf_Off offset, GElf_Xword filesz)
	  {
	    if (type == PT_LOAD)
	      final_read (offset, vaddr + bias, filesz);
	  }

	  if (ehdr.e32.e_ident[EI_CLASS] == ELFCLASS32)
	    for (uint_fast16_t i = 0; i < phnum; ++i)
	      read_phdr (phdrs.p32[i].p_type, phdrs.p32[i].p_vaddr,
			 phdrs.p32[i].p_offset, phdrs.p32[i].p_filesz);
	  else
	    for (uint_fast16_t i = 0; i < phnum; ++i)
	      read_phdr (phdrs.p64[i].p_type, phdrs.p64[i].p_vaddr,
			 phdrs.p64[i].p_offset, phdrs.p64[i].p_filesz);
	}
      else
	{
	  /* The whole file sits contiguous in memory,
	     but the caller didn't want to just do it.  */

	  const size_t have = MIN (buffer_available, file_trimmed_end);
	  memcpy (contents, buffer, have);

	  if (have < file_trimmed_end)
	    final_read (have, start + have, file_trimmed_end - have);
	}

      elf = elf_memory (contents, file_trimmed_end);
      if (unlikely (elf == NULL))
	free (contents);
      else
	elf->flags |= ELF_F_MALLOCED;
    }

  if (elf != NULL)
    {
      /* Install the file in the module.  */
      mod->main.elf = elf;
      mod->main.vaddr = module_start - bias;
      mod->main.address_sync = module_address_sync;
      mod->main_bias = bias;
    }

  return finish ();
}