glibc/malloc/hooks.c

/* Malloc implementation for multiple threads without lock contention.
   Copyright (C) 2001-2021 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Wolfram Gloger <wg@malloc.de>, 2001.

   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; see the file COPYING.LIB.  If
   not, see <https://www.gnu.org/licenses/>.  */

/* What to do if the standard debugging hooks are in place and a
   corrupt pointer is detected: do nothing (0), print an error message
   (1), or call abort() (2). */

/* Hooks for debugging versions.  The initial hooks just call the
   initialization routine, then do the normal work. */

static void *
malloc_hook_ini (size_t sz, const void *caller)
{
  __malloc_hook = NULL;
  ptmalloc_init ();
  return __libc_malloc (sz);
}

static void *
realloc_hook_ini (void *ptr, size_t sz, const void *caller)
{
  __malloc_hook = NULL;
  __realloc_hook = NULL;
  ptmalloc_init ();
  return __libc_realloc (ptr, sz);
}

static void *
memalign_hook_ini (size_t alignment, size_t sz, const void *caller)
{
  __memalign_hook = NULL;
  ptmalloc_init ();
  return __libc_memalign (alignment, sz);
}

/* Whether we are using malloc checking.  */
static int using_malloc_checking;

/* Activate a standard set of debugging hooks. */
void
__malloc_check_init (void)
{
  using_malloc_checking = 1;
  __malloc_hook = malloc_check;
  __free_hook = free_check;
  __realloc_hook = realloc_check;
  __memalign_hook = memalign_check;
}

/* When memory is tagged, the checking data is stored in the user part
   of the chunk.  We can't rely on the user not having modified the
   tags, so fetch the tag at each location before dereferencing
   it.  */
#define SAFE_CHAR_OFFSET(p,offset) \
  ((unsigned char *) tag_at (((unsigned char *) p) + offset))

/* A simple, standard set of debugging hooks.  Overhead is `only' one
   byte per chunk; still this will catch most cases of double frees or
   overruns.  The goal here is to avoid obscure crashes due to invalid
   usage, unlike in the MALLOC_DEBUG code. */

static unsigned char
magicbyte (const void *p)
{
  unsigned char magic;

  magic = (((uintptr_t) p >> 3) ^ ((uintptr_t) p >> 11)) & 0xFF;
  /* Do not return 1.  See the comment in mem2mem_check().  */
  if (magic == 1)
    ++magic;
  return magic;
}

/* Visualize the chunk as being partitioned into blocks of 255 bytes from the
   highest address of the chunk, downwards.  The end of each block tells
   us the size of that block, up to the actual size of the requested
   memory.  Our magic byte is right at the end of the requested size, so we
   must reach it with this iteration, otherwise we have witnessed a memory
   corruption.  */
static size_t
malloc_check_get_size (mchunkptr p)
{
  size_t size;
  unsigned char c;
  unsigned char magic = magicbyte (p);

  assert (using_malloc_checking == 1);

  for (size = CHUNK_HDR_SZ + memsize (p) - 1;
       (c = *SAFE_CHAR_OFFSET (p, size)) != magic;
       size -= c)
    {
      if (c <= 0 || size < (c + CHUNK_HDR_SZ))
	malloc_printerr ("malloc_check_get_size: memory corruption");
    }

  /* chunk2mem size.  */
  return size - CHUNK_HDR_SZ;
}

/* Instrument a chunk with overrun detector byte(s) and convert it
   into a user pointer with requested size req_sz. */

static void *
mem2mem_check (void *ptr, size_t req_sz)
{
  mchunkptr p;
  unsigned char *m_ptr = ptr;
  size_t max_sz, block_sz, i;
  unsigned char magic;

  if (!ptr)
    return ptr;

  p = mem2chunk (ptr);
  magic = magicbyte (p);
  max_sz = memsize (p);

  for (i = max_sz - 1; i > req_sz; i -= block_sz)
    {
      block_sz = MIN (i - req_sz, 0xff);
      /* Don't allow the magic byte to appear in the chain of length bytes.
         For the following to work, magicbyte cannot return 0x01.  */
      if (block_sz == magic)
        --block_sz;

      *SAFE_CHAR_OFFSET (m_ptr, i) = block_sz;
    }
  *SAFE_CHAR_OFFSET (m_ptr, req_sz) = magic;
  return (void *) m_ptr;
}

/* Convert a pointer to be free()d or realloc()ed to a valid chunk
   pointer.  If the provided pointer is not valid, return NULL. */

static mchunkptr
mem2chunk_check (void *mem, unsigned char **magic_p)
{
  mchunkptr p;
  INTERNAL_SIZE_T sz, c;
  unsigned char magic;

  if (!aligned_OK (mem))
    return NULL;

  p = mem2chunk (mem);
  sz = chunksize (p);
  magic = magicbyte (p);
  if (!chunk_is_mmapped (p))
    {
      /* Must be a chunk in conventional heap memory. */
      int contig = contiguous (&main_arena);
      if ((contig &&
           ((char *) p < mp_.sbrk_base ||
            ((char *) p + sz) >= (mp_.sbrk_base + main_arena.system_mem))) ||
          sz < MINSIZE || sz & MALLOC_ALIGN_MASK || !inuse (p) ||
          (!prev_inuse (p) && ((prev_size (p) & MALLOC_ALIGN_MASK) != 0 ||
                               (contig && (char *) prev_chunk (p) < mp_.sbrk_base) ||
                               next_chunk (prev_chunk (p)) != p)))
        return NULL;

      for (sz = CHUNK_HDR_SZ + memsize (p) - 1;
	   (c = *SAFE_CHAR_OFFSET (p, sz)) != magic;
	   sz -= c)
        {
          if (c == 0 || sz < (c + CHUNK_HDR_SZ))
            return NULL;
        }
    }
  else
    {
      unsigned long offset, page_mask = GLRO (dl_pagesize) - 1;

      /* mmap()ed chunks have MALLOC_ALIGNMENT or higher power-of-two
         alignment relative to the beginning of a page.  Check this
         first. */
      offset = (unsigned long) mem & page_mask;
      if ((offset != MALLOC_ALIGNMENT && offset != 0 && offset != 0x10 &&
           offset != 0x20 && offset != 0x40 && offset != 0x80 && offset != 0x100 &&
           offset != 0x200 && offset != 0x400 && offset != 0x800 && offset != 0x1000 &&
           offset < 0x2000) ||
          !chunk_is_mmapped (p) || prev_inuse (p) ||
          ((((unsigned long) p - prev_size (p)) & page_mask) != 0) ||
          ((prev_size (p) + sz) & page_mask) != 0)
        return NULL;

      for (sz = CHUNK_HDR_SZ + memsize (p) - 1;
	   (c = *SAFE_CHAR_OFFSET (p, sz)) != magic;
	   sz -= c)
        {
          if (c == 0 || sz < (c + CHUNK_HDR_SZ))
            return NULL;
        }
    }

  unsigned char* safe_p = SAFE_CHAR_OFFSET (p, sz);
  *safe_p ^= 0xFF;
  if (magic_p)
    *magic_p = safe_p;
  return p;
}

/* Check for corruption of the top chunk.  */
static void
top_check (void)
{
  mchunkptr t = top (&main_arena);

  if (t == initial_top (&main_arena) ||
      (!chunk_is_mmapped (t) &&
       chunksize (t) >= MINSIZE &&
       prev_inuse (t) &&
       (!contiguous (&main_arena) ||
        (char *) t + chunksize (t) == mp_.sbrk_base + main_arena.system_mem)))
    return;

  malloc_printerr ("malloc: top chunk is corrupt");
}

static void *
malloc_check (size_t sz, const void *caller)
{
  void *victim;
  size_t nb;

  if (__builtin_add_overflow (sz, 1, &nb))
    {
      __set_errno (ENOMEM);
      return NULL;
    }

  __libc_lock_lock (main_arena.mutex);
  top_check ();
  victim = _int_malloc (&main_arena, nb);
  __libc_lock_unlock (main_arena.mutex);
  return mem2mem_check (tag_new_usable (victim), sz);
}

static void
free_check (void *mem, const void *caller)
{
  mchunkptr p;

  if (!mem)
    return;

  int err = errno;

  /* Quickly check that the freed pointer matches the tag for the memory.
     This gives a useful double-free detection.  */
  if (__glibc_unlikely (mtag_enabled))
    *(volatile char *)mem;

  __libc_lock_lock (main_arena.mutex);
  p = mem2chunk_check (mem, NULL);
  if (!p)
    malloc_printerr ("free(): invalid pointer");
  if (chunk_is_mmapped (p))
    {
      __libc_lock_unlock (main_arena.mutex);
      munmap_chunk (p);
    }
  else
    {
      /* Mark the chunk as belonging to the library again.  */
      (void)tag_region (chunk2mem (p), memsize (p));
      _int_free (&main_arena, p, 1);
      __libc_lock_unlock (main_arena.mutex);
    }
  __set_errno (err);
}

static void *
realloc_check (void *oldmem, size_t bytes, const void *caller)
{
  INTERNAL_SIZE_T chnb;
  void *newmem = 0;
  unsigned char *magic_p;
  size_t rb;

  if (__builtin_add_overflow (bytes, 1, &rb))
    {
      __set_errno (ENOMEM);
      return NULL;
    }
  if (oldmem == 0)
    return malloc_check (bytes, NULL);

  if (bytes == 0)
    {
      free_check (oldmem, NULL);
      return NULL;
    }

  /* Quickly check that the freed pointer matches the tag for the memory.
     This gives a useful double-free detection.  */
  if (__glibc_unlikely (mtag_enabled))
    *(volatile char *)oldmem;

  __libc_lock_lock (main_arena.mutex);
  const mchunkptr oldp = mem2chunk_check (oldmem, &magic_p);
  __libc_lock_unlock (main_arena.mutex);
  if (!oldp)
    malloc_printerr ("realloc(): invalid pointer");
  const INTERNAL_SIZE_T oldsize = chunksize (oldp);

  if (!checked_request2size (rb, &chnb))
    goto invert;

  __libc_lock_lock (main_arena.mutex);

  if (chunk_is_mmapped (oldp))
    {
#if HAVE_MREMAP
      mchunkptr newp = mremap_chunk (oldp, chnb);
      if (newp)
        newmem = chunk2mem_tag (newp);
      else
#endif
      {
	/* Note the extra SIZE_SZ overhead. */
        if (oldsize - SIZE_SZ >= chnb)
          newmem = oldmem; /* do nothing */
        else
          {
            /* Must alloc, copy, free. */
	    top_check ();
	    newmem = _int_malloc (&main_arena, rb);
            if (newmem)
              {
                memcpy (newmem, oldmem, oldsize - CHUNK_HDR_SZ);
                munmap_chunk (oldp);
              }
          }
      }
    }
  else
    {
      top_check ();
      newmem = _int_realloc (&main_arena, oldp, oldsize, chnb);
    }

  DIAG_PUSH_NEEDS_COMMENT;
#if __GNUC_PREREQ (7, 0)
  /* GCC 7 warns about magic_p may be used uninitialized.  But we never
     reach here if magic_p is uninitialized.  */
  DIAG_IGNORE_NEEDS_COMMENT (7, "-Wmaybe-uninitialized");
#endif
  /* mem2chunk_check changed the magic byte in the old chunk.
     If newmem is NULL, then the old chunk will still be used though,
     so we need to invert that change here.  */
invert:
  if (newmem == NULL)
    *magic_p ^= 0xFF;
  DIAG_POP_NEEDS_COMMENT;

  __libc_lock_unlock (main_arena.mutex);

  return mem2mem_check (tag_new_usable (newmem), bytes);
}

static void *
memalign_check (size_t alignment, size_t bytes, const void *caller)
{
  void *mem;

  if (alignment <= MALLOC_ALIGNMENT)
    return malloc_check (bytes, NULL);

  if (alignment < MINSIZE)
    alignment = MINSIZE;

  /* If the alignment is greater than SIZE_MAX / 2 + 1 it cannot be a
     power of 2 and will cause overflow in the check below.  */
  if (alignment > SIZE_MAX / 2 + 1)
    {
      __set_errno (EINVAL);
      return 0;
    }

  /* Check for overflow.  */
  if (bytes > SIZE_MAX - alignment - MINSIZE)
    {
      __set_errno (ENOMEM);
      return 0;
    }

  /* Make sure alignment is power of 2.  */
  if (!powerof2 (alignment))
    {
      size_t a = MALLOC_ALIGNMENT * 2;
      while (a < alignment)
        a <<= 1;
      alignment = a;
    }

  __libc_lock_lock (main_arena.mutex);
  top_check ();
  mem = _int_memalign (&main_arena, alignment, bytes + 1);
  __libc_lock_unlock (main_arena.mutex);
  return mem2mem_check (tag_new_usable (mem), bytes);
}

#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_25)

/* Support for restoring dumped heaps contained in historic Emacs
   executables.  The heap saving feature (malloc_get_state) is no
   longer implemented in this version of glibc, but we have a heap
   rewriter in malloc_set_state which transforms the heap into a
   version compatible with current malloc.  */

#define MALLOC_STATE_MAGIC   0x444c4541l
#define MALLOC_STATE_VERSION (0 * 0x100l + 5l) /* major*0x100 + minor */

struct malloc_save_state
{
  long magic;
  long version;
  mbinptr av[NBINS * 2 + 2];
  char *sbrk_base;
  int sbrked_mem_bytes;
  unsigned long trim_threshold;
  unsigned long top_pad;
  unsigned int n_mmaps_max;
  unsigned long mmap_threshold;
  int check_action;
  unsigned long max_sbrked_mem;
  unsigned long max_total_mem;	/* Always 0, for backwards compatibility.  */
  unsigned int n_mmaps;
  unsigned int max_n_mmaps;
  unsigned long mmapped_mem;
  unsigned long max_mmapped_mem;
  int using_malloc_checking;
  unsigned long max_fast;
  unsigned long arena_test;
  unsigned long arena_max;
  unsigned long narenas;
};

/* Dummy implementation which always fails.  We need to provide this
   symbol so that existing Emacs binaries continue to work with
   BIND_NOW.  */
void *
attribute_compat_text_section
malloc_get_state (void)
{
  __set_errno (ENOSYS);
  return NULL;
}
compat_symbol (libc, malloc_get_state, malloc_get_state, GLIBC_2_0);

int
attribute_compat_text_section
malloc_set_state (void *msptr)
{
  struct malloc_save_state *ms = (struct malloc_save_state *) msptr;

  if (ms->magic != MALLOC_STATE_MAGIC)
    return -1;

  /* Must fail if the major version is too high. */
  if ((ms->version & ~0xffl) > (MALLOC_STATE_VERSION & ~0xffl))
    return -2;

  /* We do not need to perform locking here because malloc_set_state
     must be called before the first call into the malloc subsytem
     (usually via __malloc_initialize_hook).  pthread_create always
     calls calloc and thus must be called only afterwards, so there
     cannot be more than one thread when we reach this point.  */

  /* Disable the malloc hooks (and malloc checking).  */
  __malloc_hook = NULL;
  __realloc_hook = NULL;
  __free_hook = NULL;
  __memalign_hook = NULL;
  using_malloc_checking = 0;

  /* Patch the dumped heap.  We no longer try to integrate into the
     existing heap.  Instead, we mark the existing chunks as mmapped.
     Together with the update to dumped_main_arena_start and
     dumped_main_arena_end, realloc and free will recognize these
     chunks as dumped fake mmapped chunks and never free them.  */

  /* Find the chunk with the lowest address with the heap.  */
  mchunkptr chunk = NULL;
  {
    size_t *candidate = (size_t *) ms->sbrk_base;
    size_t *end = (size_t *) (ms->sbrk_base + ms->sbrked_mem_bytes);
    while (candidate < end)
      if (*candidate != 0)
	{
	  chunk = mem2chunk ((void *) (candidate + 1));
	  break;
	}
      else
	++candidate;
  }
  if (chunk == NULL)
    return 0;

  /* Iterate over the dumped heap and patch the chunks so that they
     are treated as fake mmapped chunks.  */
  mchunkptr top = ms->av[2];
  while (chunk < top)
    {
      if (inuse (chunk))
	{
	  /* Mark chunk as mmapped, to trigger the fallback path.  */
	  size_t size = chunksize (chunk);
	  set_head (chunk, size | IS_MMAPPED);
	}
      chunk = next_chunk (chunk);
    }

  /* The dumped fake mmapped chunks all lie in this address range.  */
  dumped_main_arena_start = (mchunkptr) ms->sbrk_base;
  dumped_main_arena_end = top;

  return 0;
}
compat_symbol (libc, malloc_set_state, malloc_set_state, GLIBC_2_0);

#endif	/* SHLIB_COMPAT */

/*
 * Local variables:
 * c-basic-offset: 2
 * End:
 */