glibc/elf/dl-minimal.c

/* Minimal replacements for basic facilities used in the dynamic linker.
   Copyright (C) 1995-2020 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/>.  */

#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <tls.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/types.h>
#include <ldsodefs.h>
#include <dl-irel.h>
#include <dl-hash.h>
#include <dl-sym-post.h>
#include <_itoa.h>
#include <malloc/malloc-internal.h>

#include <assert.h>

/* The rtld startup code calls __rtld_malloc_init_stubs after the
  first self-relocation to adjust the pointers to the minimal
  implementation below.  Before the final relocation,
  __rtld_malloc_init_real is called to replace the pointers with the
  real implementation.  */
__typeof (calloc) *__rtld_calloc attribute_relro;
__typeof (free) *__rtld_free attribute_relro;
__typeof (malloc) *__rtld_malloc attribute_relro;
__typeof (realloc) *__rtld_realloc attribute_relro;

/* Defined below.  */
static __typeof (calloc) rtld_calloc;
static __typeof (free) rtld_free;
static __typeof (malloc) rtld_malloc;
static __typeof (realloc) rtld_realloc;

void
__rtld_malloc_init_stubs (void)
{
  __rtld_calloc = &rtld_calloc;
  __rtld_free = &rtld_free;
  __rtld_malloc = &rtld_malloc;
  __rtld_realloc = &rtld_realloc;
}

bool
__rtld_malloc_is_complete (void)
{
  /* The caller assumes that there is an active malloc.  */
  assert (__rtld_malloc != NULL);
  return __rtld_malloc != &rtld_malloc;
}

/* Lookup NAME at VERSION in the scope of MATCH.  */
static void *
lookup_malloc_symbol (struct link_map *main_map, const char *name,
		      struct r_found_version *version)
{

  const ElfW(Sym) *ref = NULL;
  lookup_t result = _dl_lookup_symbol_x (name, main_map, &ref,
					 main_map->l_scope,
					 version, 0, 0, NULL);

  assert (ELFW(ST_TYPE) (ref->st_info) != STT_TLS);
  void *value = DL_SYMBOL_ADDRESS (result, ref);

  return _dl_sym_post (result, ref, value, 0, main_map);
}

void
__rtld_malloc_init_real (struct link_map *main_map)
{
  /* We cannot use relocations and initializers for this because the
     changes made by __rtld_malloc_init_stubs break REL-style
     (non-RELA) relocations that depend on the previous pointer
     contents.  Also avoid direct relocation depedencies for the
     malloc symbols so this function can be called before the final
     rtld relocation (which enables RELRO, after which the pointer
     variables cannot be written to).  */

  struct r_found_version version;
  version.name = symbol_version_string (libc, GLIBC_2_0);
  version.hidden = 0;
  version.hash = _dl_elf_hash (version.name);
  version.filename = NULL;

  void *new_calloc = lookup_malloc_symbol (main_map, "calloc", &version);
  void *new_free = lookup_malloc_symbol (main_map, "free", &version);
  void *new_malloc = lookup_malloc_symbol (main_map, "malloc", &version);
  void *new_realloc = lookup_malloc_symbol (main_map, "realloc", &version);

  /* Update the pointers in one go, so that any internal allocations
     performed by lookup_malloc_symbol see a consistent
     implementation.  */
  __rtld_calloc = new_calloc;
  __rtld_free = new_free;
  __rtld_malloc = new_malloc;
  __rtld_realloc = new_realloc;
}

/* Minimal malloc allocator for used during initial link.  After the
   initial link, a full malloc implementation is interposed, either
   the one in libc, or a different one supplied by the user through
   interposition.  */

static void *alloc_ptr, *alloc_end, *alloc_last_block;

/* Allocate an aligned memory block.  */
static void *
rtld_malloc (size_t n)
{
  if (alloc_end == 0)
    {
      /* Consume any unused space in the last page of our data segment.  */
      extern int _end attribute_hidden;
      alloc_ptr = &_end;
      alloc_end = (void *) 0 + (((alloc_ptr - (void *) 0)
				 + GLRO(dl_pagesize) - 1)
				& ~(GLRO(dl_pagesize) - 1));
    }

  /* Make sure the allocation pointer is ideally aligned.  */
  alloc_ptr = (void *) 0 + (((alloc_ptr - (void *) 0) + MALLOC_ALIGNMENT - 1)
			    & ~(MALLOC_ALIGNMENT - 1));

  if (alloc_ptr + n >= alloc_end || n >= -(uintptr_t) alloc_ptr)
    {
      /* Insufficient space left; allocate another page plus one extra
	 page to reduce number of mmap calls.  */
      caddr_t page;
      size_t nup = (n + GLRO(dl_pagesize) - 1) & ~(GLRO(dl_pagesize) - 1);
      if (__glibc_unlikely (nup == 0 && n != 0))
	return NULL;
      nup += GLRO(dl_pagesize);
      page = __mmap (0, nup, PROT_READ|PROT_WRITE,
		     MAP_ANON|MAP_PRIVATE, -1, 0);
      if (page == MAP_FAILED)
	return NULL;
      if (page != alloc_end)
	alloc_ptr = page;
      alloc_end = page + nup;
    }

  alloc_last_block = (void *) alloc_ptr;
  alloc_ptr += n;
  return alloc_last_block;
}

/* We use this function occasionally since the real implementation may
   be optimized when it can assume the memory it returns already is
   set to NUL.  */
static void *
rtld_calloc (size_t nmemb, size_t size)
{
  /* New memory from the trivial malloc above is always already cleared.
     (We make sure that's true in the rare occasion it might not be,
     by clearing memory in free, below.)  */
  size_t bytes = nmemb * size;

#define HALF_SIZE_T (((size_t) 1) << (8 * sizeof (size_t) / 2))
  if (__builtin_expect ((nmemb | size) >= HALF_SIZE_T, 0)
      && size != 0 && bytes / size != nmemb)
    return NULL;

  return malloc (bytes);
}

/* This will rarely be called.  */
void
rtld_free (void *ptr)
{
  /* We can free only the last block allocated.  */
  if (ptr == alloc_last_block)
    {
      /* Since this is rare, we clear the freed block here
	 so that calloc can presume malloc returns cleared memory.  */
      memset (alloc_last_block, '\0', alloc_ptr - alloc_last_block);
      alloc_ptr = alloc_last_block;
    }
}

/* This is only called with the most recent block returned by malloc.  */
void *
rtld_realloc (void *ptr, size_t n)
{
  if (ptr == NULL)
    return malloc (n);
  assert (ptr == alloc_last_block);
  size_t old_size = alloc_ptr - alloc_last_block;
  alloc_ptr = alloc_last_block;
  void *new = malloc (n);
  return new != ptr ? memcpy (new, ptr, old_size) : new;
}

/* Avoid signal frobnication in setjmp/longjmp.  Keeps things smaller.  */

#include <setjmp.h>

int weak_function
__sigjmp_save (sigjmp_buf env, int savemask __attribute__ ((unused)))
{
  env[0].__mask_was_saved = 0;
  return 0;
}

/* Define our own version of the internal function used by strerror.  We
   only provide the messages for some common errors.  This avoids pulling
   in the whole error list.  */

char * weak_function
__strerror_r (int errnum, char *buf, size_t buflen)
{
  char *msg;

  switch (errnum)
    {
    case ENOMEM:
      msg = (char *) "Cannot allocate memory";
      break;
    case EINVAL:
      msg = (char *) "Invalid argument";
      break;
    case ENOENT:
      msg = (char *) "No such file or directory";
      break;
    case EPERM:
      msg = (char *) "Operation not permitted";
      break;
    case EIO:
      msg = (char *) "Input/output error";
      break;
    case EACCES:
      msg = (char *) "Permission denied";
      break;
    default:
      /* No need to check buffer size, all calls in the dynamic linker
	 provide enough space.  */
      buf[buflen - 1] = '\0';
      msg = _itoa (errnum, buf + buflen - 1, 10, 0);
      msg = memcpy (msg - (sizeof ("Error ") - 1), "Error ",
		    sizeof ("Error ") - 1);
      break;
    }

  return msg;
}

void
__libc_fatal (const char *message)
{
  _dl_fatal_printf ("%s", message);
}
rtld_hidden_def (__libc_fatal)

void
__attribute__ ((noreturn))
__chk_fail (void)
{
  _exit (127);
}
rtld_hidden_def (__chk_fail)

#ifndef NDEBUG
/* Define (weakly) our own assert failure function which doesn't use stdio.
   If we are linked into the user program (-ldl), the normal __assert_fail
   defn can override this one.  */

void weak_function
__assert_fail (const char *assertion,
	       const char *file, unsigned int line, const char *function)
{
  _dl_fatal_printf ("\
Inconsistency detected by ld.so: %s: %u: %s%sAssertion `%s' failed!\n",
		    file, line, function ?: "", function ? ": " : "",
		    assertion);

}
rtld_hidden_weak (__assert_fail)

void weak_function
__assert_perror_fail (int errnum,
		      const char *file, unsigned int line,
		      const char *function)
{
  char errbuf[400];
  _dl_fatal_printf ("\
Inconsistency detected by ld.so: %s: %u: %s%sUnexpected error: %s.\n",
		    file, line, function ?: "", function ? ": " : "",
		    __strerror_r (errnum, errbuf, sizeof errbuf));

}
rtld_hidden_weak (__assert_perror_fail)
#endif

#undef _itoa
/* We always use _itoa instead of _itoa_word in ld.so since the former
   also has to be present and it is never about speed when these
   functions are used.  */
char *
_itoa (unsigned long long int value, char *buflim, unsigned int base,
       int upper_case)
{
  assert (! upper_case);

  do
    *--buflim = _itoa_lower_digits[value % base];
  while ((value /= base) != 0);

  return buflim;
}

/* The '_itoa_lower_digits' variable in libc.so is able to handle bases
   up to 36.  We don't need this here.  */
const char _itoa_lower_digits[16] = "0123456789abcdef";
rtld_hidden_data_def (_itoa_lower_digits)

/* The following is not a complete strsep implementation.  It cannot
   handle empty delimiter strings.  But this isn't necessary for the
   execution of ld.so.  */
#undef strsep
#undef __strsep
char *
__strsep (char **stringp, const char *delim)
{
  char *begin;

  assert (delim[0] != '\0');

  begin = *stringp;
  if (begin != NULL)
    {
      char *end = begin;

      while (*end != '\0' || (end = NULL))
	{
	  const char *dp = delim;

	  do
	    if (*dp == *end)
	      break;
	  while (*++dp != '\0');

	  if (*dp != '\0')
	    {
	      *end++ = '\0';
	      break;
	    }

	  ++end;
	}

      *stringp = end;
    }

  return begin;
}
weak_alias (__strsep, strsep)
strong_alias (__strsep, __strsep_g)