/src/elfutils/libelf/elf_compress.c

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/* Compress or decompress a section.
   Copyright (C) 2015, 2016 Red Hat, Inc.
   Copyright (C) 2023, Mark J. Wielaard <mark@klomp.org>
   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/>.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <libelf.h>
#include "libelfP.h"
#include "common.h"

#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <zlib.h>

#ifdef USE_ZSTD
#include <zstd.h>
#endif

/* Cleanup and return result.  Don't leak memory.  */
static void *
do_deflate_cleanup (void *result, z_stream *z, void *out_buf,
                    Elf_Data *cdatap)
{
  deflateEnd (z);
  free (out_buf);
  if (cdatap != NULL)
    free (cdatap->d_buf);
  return result;
}

#define deflate_cleanup(result, cdata) \
    do_deflate_cleanup(result, &z, out_buf, cdata)

static
void *
__libelf_compress_zlib (Elf_Scn *scn, size_t hsize, int ei_data,
      size_t *orig_size, size_t *orig_addralign,
      size_t *new_size, bool force,
      Elf_Data *data, Elf_Data *next_data,
      void *out_buf, size_t out_size, size_t block)
{
  /* Caller gets to fill in the header at the start.  Just skip it here.  */
  size_t used = hsize;

  z_stream z;
  z.zalloc = Z_NULL;
  z.zfree = Z_NULL;
  z.opaque = Z_NULL;
  int zrc = deflateInit (&z, Z_BEST_COMPRESSION);
  if (zrc != Z_OK)
    {
      __libelf_seterrno (ELF_E_COMPRESS_ERROR);
      return deflate_cleanup(NULL, NULL);
    }

  Elf_Data cdata;
  cdata.d_buf = NULL;

  /* Loop over data buffers.  */
  int flush = Z_NO_FLUSH;
  do
    {
      /* Convert to raw if different endianness.  */
      cdata = *data;
      bool convert = ei_data != MY_ELFDATA && data->d_size > 0;
      if (convert)
  {
    /* Don't do this conversion in place, we might want to keep
       the original data around, caller decides.  */
    cdata.d_buf = malloc (data->d_size);
    if (cdata.d_buf == NULL)
      {
        __libelf_seterrno (ELF_E_NOMEM);
        return deflate_cleanup (NULL, NULL);
      }
    if (gelf_xlatetof (scn->elf, &cdata, data, ei_data) == NULL)
      return deflate_cleanup (NULL, &cdata);
  }

      z.avail_in = cdata.d_size;
      z.next_in = cdata.d_buf;

      /* Get next buffer to see if this is the last one.  */
      data = next_data;
      if (data != NULL)
  {
    *orig_addralign = MAX (*orig_addralign, data->d_align);
    *orig_size += data->d_size;
    next_data = elf_getdata (scn, data);
  }
      else
  flush = Z_FINISH;

      /* Flush one data buffer.  */
      do
  {
    z.avail_out = out_size - used;
    z.next_out = out_buf + used;
    zrc = deflate (&z, flush);
    if (zrc == Z_STREAM_ERROR)
      {
        __libelf_seterrno (ELF_E_COMPRESS_ERROR);
        return deflate_cleanup (NULL, convert ? &cdata : NULL);
      }
    used += (out_size - used) - z.avail_out;

    /* Bail out if we are sure the user doesn't want the
       compression forced and we are using more compressed data
       than original data.  */
    if (!force && flush == Z_FINISH && used >= *orig_size)
      return deflate_cleanup ((void *) -1, convert ? &cdata : NULL);

    if (z.avail_out == 0)
      {
        void *bigger = realloc (out_buf, out_size + block);
        if (bigger == NULL)
    {
      __libelf_seterrno (ELF_E_NOMEM);
      return deflate_cleanup (NULL, convert ? &cdata : NULL);
    }
        out_buf = bigger;
        out_size += block;
      }
  }
      while (z.avail_out == 0); /* Need more output buffer.  */

      if (convert)
  {
    free (cdata.d_buf);
    cdata.d_buf = NULL;
  }
    }
  while (flush != Z_FINISH); /* More data blocks.  */

  if (zrc != Z_STREAM_END)
    {
      __libelf_seterrno (ELF_E_COMPRESS_ERROR);
      return deflate_cleanup (NULL, NULL);
    }

  deflateEnd (&z);
  *new_size = used;
  return out_buf;
}

#ifdef USE_ZSTD_COMPRESS
/* Cleanup and return result.  Don't leak memory.  */
static void *
do_zstd_cleanup (void *result, ZSTD_CCtx * const cctx, void *out_buf,
     Elf_Data *cdatap)
{
  ZSTD_freeCCtx (cctx);
  free (out_buf);
  if (cdatap != NULL)
    free (cdatap->d_buf);
  return result;
}

#define zstd_cleanup(result, cdata) \
    do_zstd_cleanup(result, cctx, out_buf, cdata)

static
void *
__libelf_compress_zstd (Elf_Scn *scn, size_t hsize, int ei_data,
      size_t *orig_size, size_t *orig_addralign,
      size_t *new_size, bool force,
      Elf_Data *data, Elf_Data *next_data,
      void *out_buf, size_t out_size, size_t block)
{
  /* Caller gets to fill in the header at the start.  Just skip it here.  */
  size_t used = hsize;

  ZSTD_CCtx* const cctx = ZSTD_createCCtx();
  Elf_Data cdata;
  cdata.d_buf = NULL;

  /* Loop over data buffers.  */
  ZSTD_EndDirective mode = ZSTD_e_continue;

  do
    {
      /* Convert to raw if different endianness.  */
      cdata = *data;
      bool convert = ei_data != MY_ELFDATA && data->d_size > 0;
      if (convert)
  {
    /* Don't do this conversion in place, we might want to keep
       the original data around, caller decides.  */
    cdata.d_buf = malloc (data->d_size);
    if (cdata.d_buf == NULL)
      {
        __libelf_seterrno (ELF_E_NOMEM);
        return zstd_cleanup (NULL, NULL);
      }
    if (gelf_xlatetof (scn->elf, &cdata, data, ei_data) == NULL)
      return zstd_cleanup (NULL, &cdata);
  }

      ZSTD_inBuffer ib = { cdata.d_buf, cdata.d_size, 0 };

      /* Get next buffer to see if this is the last one.  */
      data = next_data;
      if (data != NULL)
  {
    *orig_addralign = MAX (*orig_addralign, data->d_align);
    *orig_size += data->d_size;
    next_data = elf_getdata (scn, data);
  }
      else
  mode = ZSTD_e_end;

      /* Flush one data buffer.  */
      for (;;)
  {
    ZSTD_outBuffer ob = { out_buf + used, out_size - used, 0 };
    size_t ret = ZSTD_compressStream2 (cctx, &ob, &ib, mode);
    if (ZSTD_isError (ret))
      {
        __libelf_seterrno (ELF_E_COMPRESS_ERROR);
        return zstd_cleanup (NULL, convert ? &cdata : NULL);
      }
    used += ob.pos;

    /* Bail out if we are sure the user doesn't want the
       compression forced and we are using more compressed data
       than original data.  */
    if (!force && mode == ZSTD_e_end && used >= *orig_size)
      return zstd_cleanup ((void *) -1, convert ? &cdata : NULL);

    if (ret > 0)
      {
        void *bigger = realloc (out_buf, out_size + block);
        if (bigger == NULL)
    {
      __libelf_seterrno (ELF_E_NOMEM);
      return zstd_cleanup (NULL, convert ? &cdata : NULL);
    }
        out_buf = bigger;
        out_size += block;
      }
    else
      break;
  }

      if (convert)
  {
    free (cdata.d_buf);
    cdata.d_buf = NULL;
  }
    }
  while (mode != ZSTD_e_end); /* More data blocks.  */

  ZSTD_freeCCtx (cctx);
  *new_size = used;
  return out_buf;
}
#endif

/* Given a section, uses the (in-memory) Elf_Data to extract the
   original data size (including the given header size) and data
   alignment.  Returns a buffer that has at least hsize bytes (for the
   caller to fill in with a header) plus zlib compressed date.  Also
   returns the new buffer size in new_size (hsize + compressed data
   size).  Returns (void *) -1 when FORCE is false and the compressed
   data would be bigger than the original data.  */
void *
internal_function
__libelf_compress (Elf_Scn *scn, size_t hsize, int ei_data,
       size_t *orig_size, size_t *orig_addralign,
       size_t *new_size, bool force, bool use_zstd)
{
  /* The compressed data is the on-disk data.  We simplify the
     implementation a bit by asking for the (converted) in-memory
     data (which might be all there is if the user created it with
     elf_newdata) and then convert back to raw if needed before
     compressing.  Should be made a bit more clever to directly
     use raw if that is directly available.  */
  Elf_Data *data = elf_getdata (scn, NULL);
  if (data == NULL)
    return NULL;

  /* When not forced and we immediately know we would use more data by
     compressing, because of the header plus zlib overhead (five bytes
     per 16 KB block, plus a one-time overhead of six bytes for the
     entire stream), don't do anything.
     Size estimation for ZSTD compression would be similar.  */
  Elf_Data *next_data = elf_getdata (scn, data);
  if (next_data == NULL && !force
      && data->d_size <= hsize + 5 + 6)
    return (void *) -1;

  *orig_addralign = data->d_align;
  *orig_size = data->d_size;

  /* Guess an output block size. 1/8th of the original Elf_Data plus
     hsize.  Make the first chunk twice that size (25%), then increase
     by a block (12.5%) when necessary.  */
  size_t block = (data->d_size / 8) + hsize;
  size_t out_size = 2 * block;
  void *out_buf = malloc (out_size);
  if (out_buf == NULL)
    {
      __libelf_seterrno (ELF_E_NOMEM);
      return NULL;
    }

  if (use_zstd)
    {
#ifdef USE_ZSTD_COMPRESS
      return __libelf_compress_zstd (scn, hsize, ei_data, orig_size,
           orig_addralign, new_size, force,
           data, next_data, out_buf, out_size,
           block);
#else
    __libelf_seterrno (ELF_E_UNKNOWN_COMPRESSION_TYPE);
    return NULL;
#endif
    }
  else
    return __libelf_compress_zlib (scn, hsize, ei_data, orig_size,
           orig_addralign, new_size, force,
           data, next_data, out_buf, out_size,
           block);
}

void *
internal_function
__libelf_decompress_zlib (void *buf_in, size_t size_in, size_t size_out)
{
  /* Catch highly unlikely compression ratios so we don't allocate
     some giant amount of memory for nothing. The max compression
     factor 1032:1 comes from http://www.zlib.net/zlib_tech.html  */
  if (unlikely (size_out / 1032 > size_in))
    {
      __libelf_seterrno (ELF_E_INVALID_DATA);
      return NULL;
    }

  /* Malloc might return NULL when requesting zero size.  This is highly
     unlikely, it would only happen when the compression was forced.
     But we do need a non-NULL buffer to return and set as result.
     Just make sure to always allocate at least 1 byte.  */
  void *buf_out = malloc (size_out ?: 1);
  if (unlikely (buf_out == NULL))
    {
      __libelf_seterrno (ELF_E_NOMEM);
      return NULL;
    }

  z_stream z =
    {
      .next_in = buf_in,
      .avail_in = size_in,
      .next_out = buf_out,
      .avail_out = size_out
    };
  int zrc = inflateInit (&z);
  while (z.avail_in > 0 && likely (zrc == Z_OK))
    {
      z.next_out = buf_out + (size_out - z.avail_out);
      zrc = inflate (&z, Z_FINISH);
      if (unlikely (zrc != Z_STREAM_END))
  {
    zrc = Z_DATA_ERROR;
    break;
  }
      zrc = inflateReset (&z);
    }

  if (unlikely (zrc != Z_OK) || unlikely (z.avail_out != 0))
    {
      free (buf_out);
      buf_out = NULL;
      __libelf_seterrno (ELF_E_DECOMPRESS_ERROR);
    }

  inflateEnd(&z);
  return buf_out;
}

#ifdef USE_ZSTD
static void *
__libelf_decompress_zstd (void *buf_in, size_t size_in, size_t size_out)
{
  /* Malloc might return NULL when requesting zero size.  This is highly
     unlikely, it would only happen when the compression was forced.
     But we do need a non-NULL buffer to return and set as result.
     Just make sure to always allocate at least 1 byte.  */
  void *buf_out = malloc (size_out ?: 1);
  if (unlikely (buf_out == NULL))
    {
      __libelf_seterrno (ELF_E_NOMEM);
      return NULL;
    }

  size_t ret = ZSTD_decompress (buf_out, size_out, buf_in, size_in);
  if (unlikely (ZSTD_isError (ret)) || unlikely (ret != size_out))
    {
      free (buf_out);
      __libelf_seterrno (ELF_E_DECOMPRESS_ERROR);
      return NULL;
    }
  else
    return buf_out;
}
#endif

void *
internal_function
__libelf_decompress (int chtype, void *buf_in, size_t size_in, size_t size_out)
{
  if (chtype == ELFCOMPRESS_ZLIB)
    return __libelf_decompress_zlib (buf_in, size_in, size_out);
  else
    {
#ifdef USE_ZSTD
    return __libelf_decompress_zstd (buf_in, size_in, size_out);
#else
    __libelf_seterrno (ELF_E_UNKNOWN_COMPRESSION_TYPE);
    return NULL;
#endif
    }
}

void *
internal_function
__libelf_decompress_elf (Elf_Scn *scn, size_t *size_out, size_t *addralign)
{
  GElf_Chdr chdr;
  if (gelf_getchdr (scn, &chdr) == NULL)
    return NULL;

  bool unknown_compression = false;
  if (chdr.ch_type != ELFCOMPRESS_ZLIB)
    {
      if (chdr.ch_type != ELFCOMPRESS_ZSTD)
  unknown_compression = true;

#ifndef USE_ZSTD
      if (chdr.ch_type == ELFCOMPRESS_ZSTD)
  unknown_compression = true;
#endif
    }

  if (unknown_compression)
    {
      __libelf_seterrno (ELF_E_UNKNOWN_COMPRESSION_TYPE);
      return NULL;
    }

  if (! powerof2 (chdr.ch_addralign))
    {
      __libelf_seterrno (ELF_E_INVALID_ALIGN);
      return NULL;
    }

  /* Take the in-memory representation, so we can even handle a
     section that has just been constructed (maybe it was copied
     over from some other ELF file first with elf_newdata).  This
     is slightly inefficient when the raw data needs to be
     converted since then we'll be converting the whole buffer and
     not just Chdr.  */
  Elf_Data *data = elf_getdata (scn, NULL);
  if (data == NULL)
    return NULL;

  int elfclass = scn->elf->class;
  size_t hsize = (elfclass == ELFCLASS32
      ? sizeof (Elf32_Chdr) : sizeof (Elf64_Chdr));
  size_t size_in = data->d_size - hsize;
  void *buf_in = data->d_buf + hsize;
  void *buf_out
    = __libelf_decompress (chdr.ch_type, buf_in, size_in, chdr.ch_size);

  *size_out = chdr.ch_size;
  *addralign = chdr.ch_addralign;
  return buf_out;
}

/* Assumes buf is a malloced buffer.  */
void
internal_function
__libelf_reset_rawdata (Elf_Scn *scn, void *buf, size_t size, size_t align,
      Elf_Type type)
{
  /* This is the new raw data, replace and possibly free old data.  */
  scn->rawdata.d.d_off = 0;
  scn->rawdata.d.d_version = EV_CURRENT;
  scn->rawdata.d.d_buf = buf;
  scn->rawdata.d.d_size = size;
  scn->rawdata.d.d_align = align;
  scn->rawdata.d.d_type = type;

  /* Remove the old data.  */
  Elf_Data_List *runp = scn->data_list.next;
  while (runp != NULL)
    {
      Elf_Data_List *oldp = runp;
      runp = runp->next;
      if ((oldp->flags & ELF_F_MALLOCED) != 0)
  free (oldp);
    }
  /* Existing existing data is no longer valid.  */
  scn->data_list.next = NULL;
  scn->data_list_rear = NULL;
  if (scn->data_base != scn->rawdata_base)
    free (scn->data_base);
  scn->data_base = NULL;
  if (scn->zdata_base != buf
      && scn->zdata_base != scn->rawdata_base)
    {
      free (scn->zdata_base);
      scn->zdata_base = NULL;
    }
  if (scn->elf->map_address == NULL
      || scn->rawdata_base == scn->zdata_base
      || (scn->flags & ELF_F_MALLOCED) != 0)
    {
      free (scn->rawdata_base);
      scn->rawdata_base = NULL;
      scn->zdata_base = NULL;
    }

  scn->rawdata_base = buf;
  scn->flags |= ELF_F_MALLOCED;

  /* Pretend we (tried to) read the data from the file and setup the
     data (might have to convert the Chdr to native format).  */
  scn->data_read = 1;
  scn->flags |= ELF_F_FILEDATA;
  __libelf_set_data_list_rdlock (scn, 1);
}

int
elf_compress (Elf_Scn *scn, int type, unsigned int flags)
{
  if (scn == NULL)
    return -1;

  if ((flags & ~ELF_CHF_FORCE) != 0)
    {
      __libelf_seterrno (ELF_E_INVALID_OPERAND);
      return -1;
    }

  bool force = (flags & ELF_CHF_FORCE) != 0;

  Elf *elf = scn->elf;
  GElf_Ehdr ehdr;
  if (gelf_getehdr (elf, &ehdr) == NULL)
    return -1;

  int elfclass = elf->class;
  int elfdata = ehdr.e_ident[EI_DATA];

  Elf64_Xword sh_flags;
  Elf64_Word sh_type;
  Elf64_Xword sh_addralign;
  union shdr
  {
    Elf32_Shdr *s32;
    Elf64_Shdr *s64;
  } shdr;
  if (elfclass == ELFCLASS32)
    {
      shdr.s32 = elf32_getshdr (scn);
      if (shdr.s32 == NULL)
  return -1;

      sh_flags = shdr.s32->sh_flags;
      sh_type = shdr.s32->sh_type;
      sh_addralign = shdr.s32->sh_addralign;
    }
  else
    {
      shdr.s64 = elf64_getshdr (scn);
      if (shdr.s64 == NULL)
  return -1;

      sh_flags = shdr.s64->sh_flags;
      sh_type = shdr.s64->sh_type;
      sh_addralign = shdr.s64->sh_addralign;
    }

  if ((sh_flags & SHF_ALLOC) != 0)
    {
      __libelf_seterrno (ELF_E_INVALID_SECTION_FLAGS);
      return -1;
    }

  if (sh_type == SHT_NULL || sh_type == SHT_NOBITS)
    {
      __libelf_seterrno (ELF_E_INVALID_SECTION_TYPE);
      return -1;
    }

  int compressed = (sh_flags & SHF_COMPRESSED);
  if (type == ELFCOMPRESS_ZLIB || type == ELFCOMPRESS_ZSTD)
    {
      /* Compress/Deflate.  */
      if (compressed == 1)
  {
    __libelf_seterrno (ELF_E_ALREADY_COMPRESSED);
    return -1;
  }

      size_t hsize = (elfclass == ELFCLASS32
          ? sizeof (Elf32_Chdr) : sizeof (Elf64_Chdr));
      size_t orig_size, orig_addralign, new_size;
      void *out_buf = __libelf_compress (scn, hsize, elfdata,
           &orig_size, &orig_addralign,
           &new_size, force,
           type == ELFCOMPRESS_ZSTD);

      /* Compression would make section larger, don't change anything.  */
      if (out_buf == (void *) -1)
  return 0;

      /* Compression failed, return error.  */
      if (out_buf == NULL)
  return -1;

      /* Put the header in front of the data.  */
      if (elfclass == ELFCLASS32)
  {
    Elf32_Chdr chdr;
    chdr.ch_type = type;
    chdr.ch_size = orig_size;
    chdr.ch_addralign = orig_addralign;
    if (elfdata != MY_ELFDATA)
      {
        CONVERT (chdr.ch_type);
        CONVERT (chdr.ch_size);
        CONVERT (chdr.ch_addralign);
      }
    memcpy (out_buf, &chdr, sizeof (Elf32_Chdr));
  }
      else
  {
    Elf64_Chdr chdr;
    chdr.ch_type = type;
    chdr.ch_reserved = 0;
    chdr.ch_size = orig_size;
    chdr.ch_addralign = sh_addralign;
    if (elfdata != MY_ELFDATA)
      {
        CONVERT (chdr.ch_type);
        CONVERT (chdr.ch_reserved);
        CONVERT (chdr.ch_size);
        CONVERT (chdr.ch_addralign);
      }
    memcpy (out_buf, &chdr, sizeof (Elf64_Chdr));
  }

      /* Note we keep the sh_entsize as is, we assume it is setup
   correctly and ignored when SHF_COMPRESSED is set.  */
      if (elfclass == ELFCLASS32)
  {
    shdr.s32->sh_size = new_size;
    shdr.s32->sh_addralign = __libelf_type_align (ELFCLASS32,
              ELF_T_CHDR);
    shdr.s32->sh_flags |= SHF_COMPRESSED;
  }
      else
  {
    shdr.s64->sh_size = new_size;
    shdr.s64->sh_addralign = __libelf_type_align (ELFCLASS64,
              ELF_T_CHDR);
    shdr.s64->sh_flags |= SHF_COMPRESSED;
  }

      __libelf_reset_rawdata (scn, out_buf, new_size, 1, ELF_T_CHDR);

      /* The section is now compressed, we could keep the uncompressed
   data around, but since that might have been multiple Elf_Data
   buffers let the user uncompress it explicitly again if they
   want it to simplify bookkeeping.  */
      free (scn->zdata_base);
      scn->zdata_base = NULL;

      return 1;
    }
  else if (type == 0)
    {
      /* Decompress/Inflate.  */
      if (compressed == 0)
  {
    __libelf_seterrno (ELF_E_NOT_COMPRESSED);
    return -1;
  }

      /* If the data is already decompressed (by elf_strptr), then we
   only need to setup the rawdata and section header. XXX what
   about elf_newdata?  */
      if (scn->zdata_base == NULL)
  {
    size_t size_out, addralign;
    void *buf_out = __libelf_decompress_elf (scn, &size_out, &addralign);
    if (buf_out == NULL)
      return -1;

    scn->zdata_base = buf_out;
    scn->zdata_size = size_out;
    scn->zdata_align = addralign;
  }

      /* Note we keep the sh_entsize as is, we assume it is setup
   correctly and ignored when SHF_COMPRESSED is set.  */
      if (elfclass == ELFCLASS32)
  {
    shdr.s32->sh_size = scn->zdata_size;
    shdr.s32->sh_addralign = scn->zdata_align;
    shdr.s32->sh_flags &= ~SHF_COMPRESSED;
  }
      else
  {
    shdr.s64->sh_size = scn->zdata_size;
    shdr.s64->sh_addralign = scn->zdata_align;
    shdr.s64->sh_flags &= ~SHF_COMPRESSED;
  }

      __libelf_reset_rawdata (scn, scn->zdata_base,
            scn->zdata_size, scn->zdata_align,
            __libelf_data_type (&ehdr, sh_type,
              scn->zdata_align));

      return 1;
    }
  else
    {
      __libelf_seterrno (ELF_E_UNKNOWN_COMPRESSION_TYPE);
      return -1;
    }
}

Coverage Report

Created: 2025-08-24 06:28