path: root/sysdeps/generic/dl-cache.h

/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   Copyright (C) 1999-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef _DL_CACHE_H
#define _DL_CACHE_H

#include <endian.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>

#ifndef _DL_CACHE_DEFAULT_ID
# define _DL_CACHE_DEFAULT_ID	3
#endif

#ifndef _dl_cache_check_flags
# define _dl_cache_check_flags(flags)			\
  ((flags) == 1 || (flags) == _DL_CACHE_DEFAULT_ID)
#endif

#ifndef LD_SO_CACHE
# define LD_SO_CACHE SYSCONFDIR "/ld.so.cache"
#endif

#ifndef add_system_dir
# define add_system_dir(dir) add_dir (dir)
#endif

#define CACHEMAGIC "ld.so-1.7.0"

/* libc5 and glibc 2.0/2.1 use the same format.  For glibc 2.2 another
   format has been added in a compatible way:
   The beginning of the string table is used for the new table:
	old_magic
	nlibs
	libs[0]
	...
	libs[nlibs-1]
	pad, new magic needs to be aligned
	     - this is string[0] for the old format
	new magic - this is string[0] for the new format
	newnlibs
	...
	newlibs[0]
	...
	newlibs[newnlibs-1]
	string 1
	string 2
	...
*/
struct file_entry
{
  int32_t flags;		/* This is 1 for an ELF library.  */
  uint32_t key, value;		/* String table indices.  */
};

struct cache_file
{
  char magic[sizeof CACHEMAGIC - 1];
  unsigned int nlibs;
  struct file_entry libs[0];
};

#define CACHEMAGIC_NEW "glibc-ld.so.cache"
#define CACHE_VERSION "1.1"
#define CACHEMAGIC_VERSION_NEW CACHEMAGIC_NEW CACHE_VERSION


struct file_entry_new
{
  union
  {
    /* Fields shared with struct file_entry.  */
    struct file_entry entry;
    /* Also expose these fields directly.  */
    struct
    {
      int32_t flags;		/* This is 1 for an ELF library.  */
      uint32_t key, value;	/* String table indices.  */
    };
  };
  uint32_t osversion;		/* Required OS version.	 */
  uint64_t hwcap;		/* Hwcap entry.	 */
};

/* See flags member of struct cache_file_new below.  */
enum
  {
    /* No endianness information available.  An old ldconfig version
       without endianness support wrote the file.  */
    cache_file_new_flags_endian_unset = 0,

    /* Cache is invalid and should be ignored.  */
    cache_file_new_flags_endian_invalid = 1,

    /* Cache format is little endian.  */
    cache_file_new_flags_endian_little = 2,

    /* Cache format is big endian.  */
    cache_file_new_flags_endian_big = 3,

    /* Bit mask to extract the cache_file_new_flags_endian_*
       values.  */
    cache_file_new_flags_endian_mask = 3,

    /* Expected value of the endian bits in the flags member for the
       current architecture.  */
    cache_file_new_flags_endian_current
      = (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
	 ? cache_file_new_flags_endian_little
	 : cache_file_new_flags_endian_big),
  };

struct cache_file_new
{
  char magic[sizeof CACHEMAGIC_NEW - 1];
  char version[sizeof CACHE_VERSION - 1];
  uint32_t nlibs;		/* Number of entries.  */
  uint32_t len_strings;		/* Size of string table. */

  /* flags & cache_file_new_flags_endian_mask is one of the values
     cache_file_new_flags_endian_unset, cache_file_new_flags_endian_invalid,
     cache_file_new_flags_endian_little, cache_file_new_flags_endian_big.

     The remaining bits are unused and should be generated as zero and
     ignored by readers.  */
  uint8_t flags;

  uint8_t padding_unsed[3];	/* Not used, for future extensions.  */

  /* File offset of the extension directory.  See struct
     cache_extension below.  Must be a multiple of four.  */
  uint32_t extension_offset;

  uint32_t unused[3];		/* Leave space for future extensions
				   and align to 8 byte boundary.  */
  struct file_entry_new libs[0]; /* Entries describing libraries.  */
  /* After this the string table of size len_strings is found.	*/
};
_Static_assert (sizeof (struct cache_file_new) == 48,
		"size of struct cache_file_new");

/* Returns false if *CACHE has the wrong endianness for this
   architecture, and true if the endianness matches (or is
   unknown).  */
static inline bool
cache_file_new_matches_endian (const struct cache_file_new *cache)
{
  /* A zero value for cache->flags means that no endianness
     information is available.  */
  return cache->flags == 0
    || ((cache->flags & cache_file_new_flags_endian_big)
	== cache_file_new_flags_endian_current);
}


/* Randomly chosen magic value, which allows for additional
   consistency verification.  */
enum { cache_extension_magic = (uint32_t) -358342284 };

/* Tag values for different kinds of extension sections.  Similar to
   SHT_* constants.  */
enum cache_extension_tag
  {
   /* Array of bytes containing the glibc version that generated this
      cache file.  */
   cache_extension_tag_generator,

   /* Total number of known cache extension tags.  */
   cache_extension_count
  };

/* Element in the array following struct cache_extension.  Similar to
   an ELF section header.  */
struct cache_extension_section
{
  /* Type of the extension section.  A enum cache_extension_tag value.  */
  uint32_t tag;

  /* Extension-specific flags.  Currently generated as zero.  */
  uint32_t flags;

  /* Offset from the start of the file for the data in this extension
     section.  Specific extensions can have alignment constraints.  */
  uint32_t offset;

  /* Length in bytes of the extension data.  Specific extensions may
     have size requirements.  */
  uint32_t size;
};

/* The extension directory in the cache.  An array of struct
   cache_extension_section entries.  */
struct cache_extension
{
  uint32_t magic;		/* Always cache_extension_magic.  */
  uint32_t count;		/* Number of following entries.  */

  /* count section descriptors of type struct cache_extension_section
     follow.  */
  struct cache_extension_section sections[];
};

/* A relocated version of struct cache_extension_section.  */
struct cache_extension_loaded
{
  /* Address and size of this extension section.  base is NULL if the
     section is missing from the file.  */
  const void *base;
  size_t size;

  /* Flags from struct cache_extension_section.  */
  uint32_t flags;
};

/* All supported extension sections, relocated.  Filled in by
   cache_extension_load below.  */
struct cache_extension_all_loaded
{
  struct cache_extension_loaded sections[cache_extension_count];
};

static bool __attribute__ ((unused))
cache_extension_load (const struct cache_file_new *cache,
		      const void *file_base, size_t file_size,
		      struct cache_extension_all_loaded *loaded)
{
  memset (loaded, 0, sizeof (*loaded));
  if (cache->extension_offset == 0)
    /* No extensions present.  This is not a format error.  */
    return true;
  if ((cache->extension_offset % 4) != 0)
    /* Extension offset is misaligned.  */
    return false;
  size_t size_tmp;
  if (__builtin_add_overflow (cache->extension_offset,
			      sizeof (struct cache_extension), &size_tmp)
      || size_tmp > file_size)
    /* Extension extends beyond the end of the file.  */
    return false;
  const struct cache_extension *ext = file_base + cache->extension_offset;
  if (ext->magic != cache_extension_magic)
    return false;
  if (__builtin_mul_overflow (ext->count,
			      sizeof (struct cache_extension_section),
			      &size_tmp)
      || __builtin_add_overflow (cache->extension_offset
				 + sizeof (struct cache_extension), size_tmp,
				 &size_tmp)
      || size_tmp > file_size)
    /* Extension array extends beyond the end of the file.  */
    return false;
  for (uint32_t i = 0; i < ext->count; ++i)
    {
      if (__builtin_add_overflow (ext->sections[i].offset,
				  ext->sections[i].size, &size_tmp)
	  || size_tmp > file_size)
	/* Extension data extends beyond the end of the file.  */
	return false;

      uint32_t tag = ext->sections[i].tag;
      if (tag >= cache_extension_count)
	/* Tag is out of range and unrecognized.  */
	continue;
      loaded->sections[tag].base = file_base + ext->sections[i].offset;
      loaded->sections[tag].size = ext->sections[i].size;
      loaded->sections[tag].flags = ext->sections[i].flags;
    }
  return true;
}

/* Used to align cache_file_new.  */
#define ALIGN_CACHE(addr)				\
(((addr) + __alignof__ (struct cache_file_new) -1)	\
 & (~(__alignof__ (struct cache_file_new) - 1)))

extern int _dl_cache_libcmp (const char *p1, const char *p2) attribute_hidden;

#endif /* _DL_CACHE_H */