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541641a3de
Previously, CET was enabled by kernel before passing control to user space and the startup code must disable CET if applications or shared libraries aren't CET enabled. Since the current kernel only supports shadow stack and won't enable shadow stack before passing control to user space, we need to enable shadow stack during startup if the application and all shared library are shadow stack enabled. There is no need to disable shadow stack at startup. Shadow stack can only be enabled in a function which will never return. Otherwise, shadow stack will underflow at the function return. 1. GL(dl_x86_feature_1) is set to the CET features which are supported by the processor and are not disabled by the tunable. Only non-zero features in GL(dl_x86_feature_1) should be enabled. After enabling shadow stack with ARCH_SHSTK_ENABLE, ARCH_SHSTK_STATUS is used to check if shadow stack is really enabled. 2. Use ARCH_SHSTK_ENABLE in RTLD_START in dynamic executable. It is safe since RTLD_START never returns. 3. Call arch_prctl (ARCH_SHSTK_ENABLE) from ARCH_SETUP_TLS in static executable. Since the start function using ARCH_SETUP_TLS never returns, it is safe to enable shadow stack in ARCH_SETUP_TLS.
63 lines
2.1 KiB
C
63 lines
2.1 KiB
C
/* Linux/x86 CET initializers function.
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Copyright (C) 2018-2023 Free Software Foundation, Inc.
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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 <sys/prctl.h>
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#include <asm/prctl.h>
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static __always_inline int
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dl_cet_disable_cet (unsigned int cet_feature)
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{
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if (cet_feature != GNU_PROPERTY_X86_FEATURE_1_SHSTK)
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return -1;
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long long int kernel_feature = ARCH_SHSTK_SHSTK;
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return (int) INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_DISABLE,
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kernel_feature);
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}
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static __always_inline int
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dl_cet_lock_cet (unsigned int cet_feature)
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{
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if (cet_feature != GNU_PROPERTY_X86_FEATURE_1_SHSTK)
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return -1;
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/* Lock all SHSTK features. */
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long long int kernel_feature = -1;
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return (int) INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_LOCK,
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kernel_feature);
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}
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static __always_inline unsigned int
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dl_cet_get_cet_status (void)
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{
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unsigned long long kernel_feature;
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unsigned int status = 0;
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if (INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_STATUS,
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&kernel_feature) == 0)
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{
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if ((kernel_feature & ARCH_SHSTK_SHSTK) != 0)
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status = GNU_PROPERTY_X86_FEATURE_1_SHSTK;
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}
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return status;
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}
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/* Enable shadow stack with a macro to avoid shadow stack underflow. */
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#define ENABLE_X86_CET(cet_feature) \
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if ((cet_feature & GNU_PROPERTY_X86_FEATURE_1_SHSTK)) \
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{ \
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long long int kernel_feature = ARCH_SHSTK_SHSTK; \
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INTERNAL_SYSCALL_CALL (arch_prctl, ARCH_SHSTK_ENABLE, \
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kernel_feature); \
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}
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