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035c012e32
It turns out the startup code in csu/elf-init.c has a perfect pair of ROP gadgets (see Marco-Gisbert and Ripoll-Ripoll, "return-to-csu: A New Method to Bypass 64-bit Linux ASLR"). These functions are not needed in dynamically-linked binaries because DT_INIT/DT_INIT_ARRAY are already processed by the dynamic linker. However, the dynamic linker skipped the main program for some reason. For maximum backwards compatibility, this is not changed, and instead, the main map is consulted from __libc_start_main if the init function argument is a NULL pointer. For statically linked binaries, the old approach based on linker symbols is still used because there is nothing else available. A new symbol version __libc_start_main@@GLIBC_2.34 is introduced because new binaries running on an old libc would not run their ELF constructors, leading to difficult-to-debug issues.
124 lines
4.2 KiB
C
124 lines
4.2 KiB
C
/* Run initializers for newly loaded objects.
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Copyright (C) 1995-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <assert.h>
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#include <stddef.h>
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#include <ldsodefs.h>
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#include <elf-initfini.h>
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static void
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call_init (struct link_map *l, int argc, char **argv, char **env)
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{
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/* If the object has not been relocated, this is a bug. The
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function pointers are invalid in this case. (Executables do not
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need relocation, and neither do proxy objects.) */
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assert (l->l_real->l_relocated || l->l_real->l_type == lt_executable);
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if (l->l_init_called)
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/* This object is all done. */
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return;
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/* Avoid handling this constructor again in case we have a circular
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dependency. */
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l->l_init_called = 1;
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/* Check for object which constructors we do not run here. */
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if (__builtin_expect (l->l_name[0], 'a') == '\0'
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&& l->l_type == lt_executable)
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return;
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/* Print a debug message if wanted. */
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if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_IMPCALLS))
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_dl_debug_printf ("\ncalling init: %s\n\n",
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DSO_FILENAME (l->l_name));
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/* Now run the local constructors. There are two forms of them:
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- the one named by DT_INIT
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- the others in the DT_INIT_ARRAY.
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*/
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if (ELF_INITFINI && l->l_info[DT_INIT] != NULL)
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DL_CALL_DT_INIT(l, l->l_addr + l->l_info[DT_INIT]->d_un.d_ptr, argc, argv, env);
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/* Next see whether there is an array with initialization functions. */
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ElfW(Dyn) *init_array = l->l_info[DT_INIT_ARRAY];
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if (init_array != NULL)
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{
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unsigned int j;
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unsigned int jm;
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ElfW(Addr) *addrs;
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jm = l->l_info[DT_INIT_ARRAYSZ]->d_un.d_val / sizeof (ElfW(Addr));
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addrs = (ElfW(Addr) *) (init_array->d_un.d_ptr + l->l_addr);
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for (j = 0; j < jm; ++j)
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((dl_init_t) addrs[j]) (argc, argv, env);
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}
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}
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void
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_dl_init (struct link_map *main_map, int argc, char **argv, char **env)
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{
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ElfW(Dyn) *preinit_array = main_map->l_info[DT_PREINIT_ARRAY];
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ElfW(Dyn) *preinit_array_size = main_map->l_info[DT_PREINIT_ARRAYSZ];
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unsigned int i;
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if (__glibc_unlikely (GL(dl_initfirst) != NULL))
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{
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call_init (GL(dl_initfirst), argc, argv, env);
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GL(dl_initfirst) = NULL;
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}
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/* Don't do anything if there is no preinit array. */
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if (__builtin_expect (preinit_array != NULL, 0)
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&& preinit_array_size != NULL
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&& (i = preinit_array_size->d_un.d_val / sizeof (ElfW(Addr))) > 0)
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{
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ElfW(Addr) *addrs;
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unsigned int cnt;
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if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_IMPCALLS))
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_dl_debug_printf ("\ncalling preinit: %s\n\n",
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DSO_FILENAME (main_map->l_name));
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addrs = (ElfW(Addr) *) (preinit_array->d_un.d_ptr + main_map->l_addr);
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for (cnt = 0; cnt < i; ++cnt)
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((dl_init_t) addrs[cnt]) (argc, argv, env);
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}
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/* Stupid users forced the ELF specification to be changed. It now
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says that the dynamic loader is responsible for determining the
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order in which the constructors have to run. The constructors
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for all dependencies of an object must run before the constructor
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for the object itself. Circular dependencies are left unspecified.
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This is highly questionable since it puts the burden on the dynamic
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loader which has to find the dependencies at runtime instead of
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letting the user do it right. Stupidity rules! */
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i = main_map->l_searchlist.r_nlist;
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while (i-- > 0)
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call_init (main_map->l_initfini[i], argc, argv, env);
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#ifndef HAVE_INLINED_SYSCALLS
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/* Finished starting up. */
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_dl_starting_up = 0;
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#endif
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}
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