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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.
96 lines
3.2 KiB
ArmAsm
96 lines
3.2 KiB
ArmAsm
/* Startup code for programs linked with GNU libc.
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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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In addition to the permissions in the GNU Lesser General Public
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License, the Free Software Foundation gives you unlimited
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permission to link the compiled version of this file with other
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programs, and to distribute those programs without any restriction
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coming from the use of this file. (The GNU Lesser General Public
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License restrictions do apply in other respects; for example, they
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cover modification of the file, and distribution when not linked
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into another program.)
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Note that people who make modified versions of this file are not
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obligated to grant this special exception for their modified
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versions; it is their choice whether to do so. The GNU Lesser
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General Public License gives permission to release a modified
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version without this exception; this exception also makes it
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possible to release a modified version which carries forward this
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exception.
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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 <sysdep.h>
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/* We do not want .eh_frame info for crt1.o since crt1.o is linked
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before crtbegin.o, the file defining __EH_FRAME_BEGIN__. */
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#undef cfi_startproc
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#define cfi_startproc
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#undef cfi_endproc
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#define cfi_endproc
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/* These are the various addresses we require. */
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#ifdef PIC
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.section ".data"
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#else
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.section ".rodata"
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#endif
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.align 2
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L(start_addresses):
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.long _SDA_BASE_
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.long main
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.long 0 /* Used to be init. */
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.long 0 /* Used to be fini. */
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ASM_SIZE_DIRECTIVE(L(start_addresses))
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.section ".text"
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ENTRY(_start)
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/* Save the stack pointer, in case we're statically linked under Linux. */
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mr r9,r1
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/* Set up an initial stack frame, and clear the LR. */
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clrrwi r1,r1,4
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#ifdef PIC
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SETUP_GOT_ACCESS(r13,got_label)
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li r0,0
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#else
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li r0,0
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#endif
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stwu r1,-16(r1)
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mtlr r0
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stw r0,0(r1)
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/* Set r13 to point at the 'small data area', and put the address of
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start_addresses in r8. Also load the GOT pointer so that new PLT
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calls work, like the one to __libc_start_main. */
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#ifdef PIC
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addis r30,r13,_GLOBAL_OFFSET_TABLE_-got_label@ha
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addis r8,r13,L(start_addresses)-got_label@ha
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addi r30,r30,_GLOBAL_OFFSET_TABLE_-got_label@l
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lwzu r13, L(start_addresses)-got_label@l(r8)
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#else
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lis r8,L(start_addresses)@ha
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lwzu r13,L(start_addresses)@l(r8)
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#endif
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/* and continue in libc-start, in glibc. */
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b JUMPTARGET(__libc_start_main)
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END(_start)
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/* Define a symbol for the first piece of initialized data. */
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.section ".data"
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.globl __data_start
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__data_start:
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.long 0
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weak_alias (__data_start, data_start)
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