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Reduce the statically linked startup code [BZ #23323]

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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.
This commit is contained in:
Florian Weimer
2021-02-25 12:10:57 +01:00
parent a79328c745
commit 035c012e32
63 changed files with 275 additions and 314 deletions
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18
sysdeps/mips/start.S
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@ -96,13 +96,13 @@ ENTRY_POINT:
# if _MIPS_SIM == _ABIO32
PTR_SUBIU $29, 32
# endif
PTR_LA $7, __libc_csu_init /* init */
PTR_LA $8, __libc_csu_fini
move $7, $0 /* Used to be init. */
# if _MIPS_SIM == _ABIO32
PTR_S $8, 16($29) /* fini */
PTR_S $0, 16($29) /* Used to be fini. */
PTR_S $2, 20($29) /* rtld_fini */
PTR_S $29, 24($29) /* stack_end */
# else
move $8, $0 /* Used to be fini. */
move $9, $2 /* rtld_fini */
move $10, $29 /* stack_end */
# endif
@ -143,19 +143,17 @@ ENTRY_POINT:
/* Lay out last arguments, and call __libc_start_main(). */
# ifdef __PIC__
sw $7, 24($sp) /* stack_end */
lw $4, %got(__libc_csu_fini)($3)
lw $7, %got(__libc_csu_init)($3) /* init */
sw $4, 16($sp) /* fini */
move $4, $0 /* Used to be ini. */
sw $0, 16($sp) /* Used to be fini. */
lw $4, %got(main)($3) /* main */
lw $3, %call16(__libc_start_main)($3)
sw $2, 20($sp) /* rtld_fini */
move $25, $3
jalr $3
# else
lw $4, 1f
sw $7, 24($sp) /* stack_end */
lw $7, 2f /* init */
sw $4, 16($sp) /* fini */
move $7, $0 /* Used to be init. */
sw $0, 16($sp) /* Used to be fini. */
lw $4, 3f /* main */
sw $2, 20($sp) /* rtld_fini */
/* Load and call __libc_start_main(). */
@ -165,8 +163,6 @@ ENTRY_POINT:
hlt: b hlt /* Crash if somehow it does return. */
# ifndef __PIC__
.align 2
1: .word __libc_csu_fini
2: .word __libc_csu_init
3: .word main
4: .word __libc_start_main
# endif