elf/dl-map-segments.h

   1 /* Map in a shared object's segments.  Generic version.
   2    Copyright (C) 1995-2022 Free Software Foundation, Inc.
   3    Copyright The GNU Toolchain Authors.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <dl-load.h>
  21
  22 /* Map a segment and align it properly.  */
  23
  24 static __always_inline ElfW(Addr)
  25 _dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
  26                  const size_t maplength, int fd)
  27 {
  28   if (__glibc_likely (c->mapalign <= GLRO(dl_pagesize)))
  29     return (ElfW(Addr)) __mmap ((void *) mappref, maplength, c->prot,
  30                                 MAP_COPY|MAP_FILE, fd, c->mapoff);
  31
  32   /* If the segment alignment > the page size, allocate enough space to
  33      ensure that the segment can be properly aligned.  */
  34   ElfW(Addr) maplen = (maplength >= c->mapalign
  35                        ? (maplength + c->mapalign)
  36                        : (2 * c->mapalign));
  37   ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
  38                                               PROT_NONE,
  39                                               MAP_ANONYMOUS|MAP_PRIVATE,
  40                                               -1, 0);
  41   if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
  42     return map_start;
  43
  44   ElfW(Addr) map_start_aligned = ALIGN_UP (map_start, c->mapalign);
  45   map_start_aligned = (ElfW(Addr)) __mmap ((void *) map_start_aligned,
  46                                            maplength, c->prot,
  47                                            MAP_COPY|MAP_FILE|MAP_FIXED,
  48                                            fd, c->mapoff);
  49   if (__glibc_unlikely ((void *) map_start_aligned == MAP_FAILED))
  50     __munmap ((void *) map_start, maplen);
  51   else
  52     {
  53       /* Unmap the unused regions.  */
  54       ElfW(Addr) delta = map_start_aligned - map_start;
  55       if (delta)
  56         __munmap ((void *) map_start, delta);
  57       ElfW(Addr) map_end = map_start_aligned + maplength;
  58       map_end = ALIGN_UP (map_end, GLRO(dl_pagesize));
  59       delta = map_start + maplen - map_end;
  60       if (delta)
  61         __munmap ((void *) map_end, delta);
  62     }
  63
  64   return map_start_aligned;
  65 }
  66
  67 /* This implementation assumes (as does the corresponding implementation
  68    of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects
  69    are always laid out with all segments contiguous (or with gaps
  70    between them small enough that it's preferable to reserve all whole
  71    pages inside the gaps with PROT_NONE mappings rather than permitting
  72    other use of those parts of the address space).  */
  73
  74 static __always_inline const char *
  75 _dl_map_segments (struct link_map *l, int fd,
  76                   const ElfW(Ehdr) *header, int type,
  77                   const struct loadcmd loadcmds[], size_t nloadcmds,
  78                   const size_t maplength, bool has_holes,
  79                   struct link_map *loader)
  80 {
  81   const struct loadcmd *c = loadcmds;
  82
  83   if (__glibc_likely (type == ET_DYN))
  84     {
  85       /* This is a position-independent shared object.  We can let the
  86          kernel map it anywhere it likes, but we must have space for all
  87          the segments in their specified positions relative to the first.
  88          So we map the first segment without MAP_FIXED, but with its
  89          extent increased to cover all the segments.  Then we remove
  90          access from excess portion, and there is known sufficient space
  91          there to remap from the later segments.
  92
  93          As a refinement, sometimes we have an address that we would
  94          prefer to map such objects at; but this is only a preference,
  95          the OS can do whatever it likes. */
  96       ElfW(Addr) mappref
  97         = (ELF_PREFERRED_ADDRESS (loader, maplength,
  98                                   c->mapstart & GLRO(dl_use_load_bias))
  99            - MAP_BASE_ADDR (l));
 100
 101       /* Remember which part of the address space this object uses.  */
 102       l->l_map_start = _dl_map_segment (c, mappref, maplength, fd);
 103       if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED))
 104         return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
 105
 106       l->l_map_end = l->l_map_start + maplength;
 107       l->l_addr = l->l_map_start - c->mapstart;
 108
 109       if (has_holes)
 110         {
 111           /* Change protection on the excess portion to disallow all access;
 112              the portions we do not remap later will be inaccessible as if
 113              unallocated.  Then jump into the normal segment-mapping loop to
 114              handle the portion of the segment past the end of the file
 115              mapping.  */
 116           if (__glibc_unlikely
 117               (__mprotect ((caddr_t) (l->l_addr + c->mapend),
 118                            loadcmds[nloadcmds - 1].mapstart - c->mapend,
 119                            PROT_NONE) < 0))
 120             return DL_MAP_SEGMENTS_ERROR_MPROTECT;
 121         }
 122
 123       l->l_contiguous = 1;
 124
 125       goto postmap;
 126     }
 127
 128   /* Remember which part of the address space this object uses.  */
 129   l->l_map_start = c->mapstart + l->l_addr;
 130   l->l_map_end = l->l_map_start + maplength;
 131   l->l_contiguous = !has_holes;
 132
 133   while (c < &loadcmds[nloadcmds])
 134     {
 135       if (c->mapend > c->mapstart
 136           /* Map the segment contents from the file.  */
 137           && (__mmap ((void *) (l->l_addr + c->mapstart),
 138                       c->mapend - c->mapstart, c->prot,
 139                       MAP_FIXED|MAP_COPY|MAP_FILE,
 140                       fd, c->mapoff)
 141               == MAP_FAILED))
 142         return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
 143
 144     postmap:
 145       _dl_postprocess_loadcmd (l, header, c);
 146
 147       if (c->allocend > c->dataend)
 148         {
 149           /* Extra zero pages should appear at the end of this segment,
 150              after the data mapped from the file.   */
 151           ElfW(Addr) zero, zeroend, zeropage;
 152
 153           zero = l->l_addr + c->dataend;
 154           zeroend = l->l_addr + c->allocend;
 155           zeropage = ((zero + GLRO(dl_pagesize) - 1)
 156                       & ~(GLRO(dl_pagesize) - 1));
 157
 158           if (zeroend < zeropage)
 159             /* All the extra data is in the last page of the segment.
 160                We can just zero it.  */
 161             zeropage = zeroend;
 162
 163           if (zeropage > zero)
 164             {
 165               /* Zero the final part of the last page of the segment.  */
 166               if (__glibc_unlikely ((c->prot & PROT_WRITE) == 0))
 167                 {
 168                   /* Dag nab it.  */
 169                   if (__mprotect ((caddr_t) (zero
 170                                              & ~(GLRO(dl_pagesize) - 1)),
 171                                   GLRO(dl_pagesize), c->prot|PROT_WRITE) < 0)
 172                     return DL_MAP_SEGMENTS_ERROR_MPROTECT;
 173                 }
 174               memset ((void *) zero, '\0', zeropage - zero);
 175               if (__glibc_unlikely ((c->prot & PROT_WRITE) == 0))
 176                 __mprotect ((caddr_t) (zero & ~(GLRO(dl_pagesize) - 1)),
 177                             GLRO(dl_pagesize), c->prot);
 178             }
 179
 180           if (zeroend > zeropage)
 181             {
 182               /* Map the remaining zero pages in from the zero fill FD.  */
 183               caddr_t mapat;
 184               mapat = __mmap ((caddr_t) zeropage, zeroend - zeropage,
 185                               c->prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED,
 186                               -1, 0);
 187               if (__glibc_unlikely (mapat == MAP_FAILED))
 188                 return DL_MAP_SEGMENTS_ERROR_MAP_ZERO_FILL;
 189             }
 190         }
 191
 192       ++c;
 193     }
 194
 195   /* Notify ELF_PREFERRED_ADDRESS that we have to load this one
 196      fixed.  */
 197   ELF_FIXED_ADDRESS (loader, c->mapstart);
 198
 199   return NULL;
 200 }