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aarch64: Enable GCS in dynamic linked exe

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Use the dynamic linker start code to enable GCS in the dynamic linked
case after _dl_start returns and before _dl_start_user which marks
the point after which user code may run.

Like in the static linked case this ensures that GCS is enabled on a
top level stack frame.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Szabolcs Nagy 2023-07-14 15:49:11 +01:00 committed by Yury Khrustalev
parent b81ee54bc9
commit 01f52b11de
4 changed files with 66 additions and 6 deletions
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8
sysdeps/aarch64/Makefile
View File

@ -9,7 +9,9 @@ LDFLAGS-rtld += -Wl,-z,force-bti,--fatal-warnings
endif
ifeq ($(subdir),elf)
sysdep-dl-routines += dl-bti
sysdep-dl-routines += \
dl-bti \
dl-gcs
tests += tst-audit26 \
tst-audit27
@ -35,7 +37,9 @@ endif
ifeq ($(subdir),elf)
sysdep-rtld-routines += dl-start
sysdep-dl-routines += tlsdesc dl-tlsdesc
gen-as-const-headers += dl-link.sym
gen-as-const-headers += \
dl-link.sym \
rtld-global-offsets.sym
tests-internal += tst-ifunc-arg-1 tst-ifunc-arg-2

25
sysdeps/aarch64/dl-gcs.c Normal file
View File

@ -0,0 +1,25 @@
/* AArch64 GCS functions.
Copyright (C) 2024-2025 Free Software Foundation, Inc.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <ldsodefs.h>
/* Used to report error when prctl system call to enabled GCS fails. */
void _dl_gcs_enable_failed (int code)
{
_dl_fatal_printf ("failed to enable GCS: %d\n", -code);
}

34
sysdeps/aarch64/dl-start.S
View File

@ -18,6 +18,7 @@
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include <rtld-global-offsets.h>
ENTRY (_start)
/* Create an initial frame with 0 LR and FP */
@ -25,11 +26,33 @@ ENTRY (_start)
mov x29, #0
mov x30, #0
/* Load and relocate all library dependencies. */
mov x0, sp
PTR_ARG (0)
bl _dl_start
/* Returns user entry point in x0. */
mov PTR_REG (21), PTR_REG (0)
/* Use GL(dl_aarch64_gcs) to set the shadow stack status. */
adrp x16, _rtld_local
add PTR_REG (16), PTR_REG (16), :lo12:_rtld_local
ldr x1, [x16, GL_DL_AARCH64_GCS_OFFSET]
cbz x1, L(skip_gcs_enable)
/* Enable GCS before user code runs. Note that IFUNC resolvers and
LD_AUDIT hooks may run before, but should not create threads. */
#define PR_SET_SHADOW_STACK_STATUS 75
#define PR_SHADOW_STACK_ENABLE (1UL << 0)
mov x0, PR_SET_SHADOW_STACK_STATUS
mov x1, PR_SHADOW_STACK_ENABLE
mov x2, 0
mov x3, 0
mov x4, 0
mov x8, #SYS_ify(prctl)
svc 0x0
cbnz w0, L(failed_gcs_enable)
L(skip_gcs_enable):
.globl _dl_start_user
.type _dl_start_user, %function
_dl_start_user:
@ -40,14 +63,17 @@ _dl_start_user:
/* Compute envp. */
add PTR_REG (3), PTR_REG (2), PTR_REG (1), lsl PTR_LOG_SIZE
add PTR_REG (3), PTR_REG (3), PTR_SIZE
adrp x16, _rtld_local
add PTR_REG (16), PTR_REG (16), :lo12:_rtld_local
/* Run the init functions of the loaded modules. */
ldr PTR_REG (0), [x16]
bl _dl_init
/* Load the finalizer function. */
adrp x0, _dl_fini
add PTR_REG (0), PTR_REG (0), :lo12:_dl_fini
/* Jump to the user's entry point. */
mov x16, x21
br x16
mov x16, x21
br x16
L(failed_gcs_enable):
b _dl_gcs_enable_failed
END (_start)

5
sysdeps/aarch64/rtld-global-offsets.sym
View File

@ -3,8 +3,13 @@
#include <ldsodefs.h>
#define GLRO_offsetof(name) offsetof (struct rtld_global_ro, _##name)
#define GL_offsetof(name) offsetof (struct rtld_global, _##name)
-- Offsets of _rtld_global_ro in libc.so
GLRO_DL_HWCAP_OFFSET GLRO_offsetof (dl_hwcap)
GLRO_DL_HWCAP2_OFFSET GLRO_offsetof (dl_hwcap2)
-- Offsets of _rtld_global in libc.so
GL_DL_AARCH64_GCS_OFFSET GL_offsetof (dl_aarch64_gcs)