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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.
103 lines
3.1 KiB
C
103 lines
3.1 KiB
C
/* Copyright (C) 1998-2021 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 <stdlib.h>
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#include <unistd.h>
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#include <ldsodefs.h>
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#include <sysdep.h>
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#ifndef SHARED
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#include <hwcapinfo.h>
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#endif
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/* The main work is done in the generic function. */
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#define LIBC_START_MAIN generic_start_main
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#define LIBC_START_DISABLE_INLINE
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#define LIBC_START_MAIN_AUXVEC_ARG
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#define MAIN_AUXVEC_ARG
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#define INIT_MAIN_ARGS
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#include <csu/libc-start.c>
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struct startup_info
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{
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void *sda_base;
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int (*main) (int, char **, char **, void *);
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int (*init) (int, char **, char **, void *);
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void (*fini) (void);
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};
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int
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__libc_start_main_impl (int argc, char **argv,
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char **ev,
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ElfW (auxv_t) * auxvec,
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void (*rtld_fini) (void),
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struct startup_info *stinfo,
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char **stack_on_entry)
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{
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/* the PPC SVR4 ABI says that the top thing on the stack will
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be a NULL pointer, so if not we assume that we're being called
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as a statically-linked program by Linux... */
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if (*stack_on_entry != NULL)
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{
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char **temp;
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/* ...in which case, we have argc as the top thing on the
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stack, followed by argv (NULL-terminated), envp (likewise),
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and the auxiliary vector. */
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/* 32/64-bit agnostic load from stack */
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argc = *(long int *) stack_on_entry;
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argv = stack_on_entry + 1;
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ev = argv + argc + 1;
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#ifdef HAVE_AUX_VECTOR
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temp = ev;
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while (*temp != NULL)
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++temp;
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auxvec = (ElfW (auxv_t) *)++ temp;
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#endif
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rtld_fini = NULL;
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}
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for (ElfW (auxv_t) * av = auxvec; av->a_type != AT_NULL; ++av)
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switch (av->a_type)
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{
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/* For the static case, we also need _dl_hwcap, _dl_hwcap2 and
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_dl_platform, so we can call
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__tcb_parse_hwcap_and_convert_at_platform (). */
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#ifndef SHARED
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case AT_HWCAP:
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_dl_hwcap = (unsigned long int) av->a_un.a_val;
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break;
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case AT_HWCAP2:
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_dl_hwcap2 = (unsigned long int) av->a_un.a_val;
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break;
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case AT_PLATFORM:
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_dl_platform = (void *) av->a_un.a_val;
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break;
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#endif
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}
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/* Initialize hwcap/hwcap2 and platform data so it can be copied to
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the TCB later in __libc_setup_tls (). (static case only). */
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#ifndef SHARED
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__tcb_parse_hwcap_and_convert_at_platform ();
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#endif
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return generic_start_main (stinfo->main, argc, argv, auxvec,
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stinfo->init, stinfo->fini, rtld_fini,
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stack_on_entry);
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}
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DEFINE_LIBC_START_MAIN_VERSION
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