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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.
182 lines
5.3 KiB
ArmAsm
182 lines
5.3 KiB
ArmAsm
/* Startup code compliant to the ELF Mips ABI.
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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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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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#define __ASSEMBLY__ 1
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#include <entry.h>
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#include <sgidefs.h>
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#include <sys/asm.h>
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#ifndef ENTRY_POINT
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#error ENTRY_POINT needs to be defined for start.S on MIPS/ELF.
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#endif
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/* This is the canonical entry point, usually the first thing in the text
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segment. The SVR4/Mips ABI (pages 3-31, 3-32) says that when the entry
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point runs, most registers' values are unspecified, except for:
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v0 ($2) Contains a function pointer to be registered with `atexit'.
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This is how the dynamic linker arranges to have DT_FINI
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functions called for shared libraries that have been loaded
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before this code runs.
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sp ($29) The stack contains the arguments and environment:
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0(%esp) argc
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4(%esp) argv[0]
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...
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(4*argc)(%esp) NULL
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(4*(argc+1))(%esp) envp[0]
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...
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NULL
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ra ($31) The return address register is set to zero so that programs
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that search backword through stack frames recognize the last
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stack frame.
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*/
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/* We need to call:
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__libc_start_main (int (*main) (int, char **, char **), int argc,
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char **argv, void (*init) (void), void (*fini) (void),
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void (*rtld_fini) (void), void *stack_end)
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*/
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.text
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.globl ENTRY_POINT
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.type ENTRY_POINT,@function
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#ifndef __mips16
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ENTRY_POINT:
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# ifdef __PIC__
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SETUP_GPX($0)
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SETUP_GPX64($25,$0)
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# else
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PTR_LA $28, _gp /* Setup GP correctly if we're non-PIC. */
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move $31, $0
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# endif
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PTR_LA $4, main /* main */
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PTR_L $5, 0($29) /* argc */
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PTR_ADDIU $6, $29, PTRSIZE /* argv */
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/* Allocate space on the stack for seven arguments (o32 only)
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and make sure the stack is aligned to double words (8 bytes)
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on o32 and quad words (16 bytes) on n32 and n64. */
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and $29, -2 * SZREG
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# if _MIPS_SIM == _ABIO32
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PTR_SUBIU $29, 32
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# endif
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move $7, $0 /* Used to be init. */
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# if _MIPS_SIM == _ABIO32
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PTR_S $0, 16($29) /* Used to be fini. */
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PTR_S $2, 20($29) /* rtld_fini */
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PTR_S $29, 24($29) /* stack_end */
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# else
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move $8, $0 /* Used to be fini. */
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move $9, $2 /* rtld_fini */
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move $10, $29 /* stack_end */
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# endif
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PTR_LA $25, __libc_start_main
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jalr $25
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hlt: b hlt /* Crash if somehow it does return. */
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#elif _MIPS_SIM == _ABIO32 /* __mips16 */
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/* MIPS16 entry point. */
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.set mips16
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ENTRY_POINT:
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# ifdef __PIC__
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li $3, %hi(_gp_disp)
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addiu $4, $pc, %lo(_gp_disp)
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sll $3, 16
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addu $3, $4
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move $gp, $3
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# else
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li $3, %hi(_gp)
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sll $3, 16
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addiu $3, %lo(_gp)
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move $gp, $3
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# endif
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/* Tie end of stack frames. */
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li $4, 0
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move $31, $4
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/* Create new SP value in $7, including alignment. */
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li $4, 2 * SZREG
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neg $4, $4
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move $7, $sp
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and $7, $4
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addiu $7, -32
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/* Load arguments with original SP. */
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lw $5, 0($sp)
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addiu $6, $sp, PTRSIZE
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/* Update SP. */
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move $sp, $7
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/* Lay out last arguments, and call __libc_start_main(). */
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# ifdef __PIC__
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sw $7, 24($sp) /* stack_end */
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move $4, $0 /* Used to be ini. */
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sw $0, 16($sp) /* Used to be fini. */
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lw $4, %got(main)($3) /* main */
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lw $3, %call16(__libc_start_main)($3)
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sw $2, 20($sp) /* rtld_fini */
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move $25, $3
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jalr $3
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# else
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sw $7, 24($sp) /* stack_end */
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move $7, $0 /* Used to be init. */
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sw $0, 16($sp) /* Used to be fini. */
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lw $4, 3f /* main */
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sw $2, 20($sp) /* rtld_fini */
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/* Load and call __libc_start_main(). */
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lw $3, 4f
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jalr $3
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# endif
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hlt: b hlt /* Crash if somehow it does return. */
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# ifndef __PIC__
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.align 2
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3: .word main
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4: .word __libc_start_main
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# endif
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#else /* __mips16 && _MIPS_SIM != _ABIO32 */
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# error "MIPS16 support for N32/N64 not implemented"
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#endif /* __mips16 */
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/* Define a symbol for the first piece of initialized data. */
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.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 data_start
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data_start = __data_start
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