sysdeps/aarch64/dl-bti.c

   1 /* AArch64 BTI functions.
   2    Copyright (C) 2020-2023 Free Software Foundation, Inc.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <unistd.h>
  19 #include <errno.h>
  20 #include <libintl.h>
  21 #include <ldsodefs.h>
  22 #include <sys/mman.h>
  23
  24 /* See elf/dl-load.h.  */
  25 #ifndef MAP_COPY
  26 # define MAP_COPY (MAP_PRIVATE | MAP_DENYWRITE)
  27 #endif
  28
  29 /* Enable BTI protection for MAP.  */
  30
  31 void
  32 _dl_bti_protect (struct link_map *map, int fd)
  33 {
  34   const size_t pagesz = GLRO(dl_pagesize);
  35   const ElfW(Phdr) *phdr;
  36
  37   for (phdr = map->l_phdr; phdr < &map->l_phdr[map->l_phnum]; ++phdr)
  38     if (phdr->p_type == PT_LOAD && (phdr->p_flags & PF_X))
  39       {
  40         size_t vstart = ALIGN_DOWN (phdr->p_vaddr, pagesz);
  41         size_t vend = ALIGN_UP (phdr->p_vaddr + phdr->p_filesz, pagesz);
  42         off_t off = ALIGN_DOWN (phdr->p_offset, pagesz);
  43         void *start = (void *) (vstart + map->l_addr);
  44         size_t len = vend - vstart;
  45
  46         unsigned prot = PROT_EXEC | PROT_BTI;
  47         if (phdr->p_flags & PF_R)
  48           prot |= PROT_READ;
  49         if (phdr->p_flags & PF_W)
  50           prot |= PROT_WRITE;
  51
  52         if (fd == -1)
  53           /* Ignore failures for kernel mapped binaries.  */
  54           __mprotect (start, len, prot);
  55         else
  56           map->l_mach.bti_fail = __mmap (start, len, prot,
  57                                          MAP_FIXED|MAP_COPY|MAP_FILE,
  58                                          fd, off) == MAP_FAILED;
  59       }
  60 }
  61
  62
  63 static void
  64 bti_failed (struct link_map *l, const char *program)
  65 {
  66   if (program)
  67     _dl_fatal_printf ("%s: %s: failed to turn on BTI protection\n",
  68                       program, l->l_name);
  69   else
  70     /* Note: the errno value is not available any more.  */
  71     _dl_signal_error (0, l->l_name, "dlopen",
  72                       N_("failed to turn on BTI protection"));
  73 }
  74
  75
  76 /* Enable BTI for L and its dependencies.  */
  77
  78 void
  79 _dl_bti_check (struct link_map *l, const char *program)
  80 {
  81   if (!GLRO(dl_aarch64_cpu_features).bti)
  82     return;
  83
  84   if (l->l_mach.bti_fail)
  85     bti_failed (l, program);
  86
  87   unsigned int i = l->l_searchlist.r_nlist;
  88   while (i-- > 0)
  89     {
  90       struct link_map *dep = l->l_initfini[i];
  91       if (dep->l_mach.bti_fail)
  92         bti_failed (dep, program);
  93     }
  94 }