From: Kees Cook <keescook@chromium.org>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
Dave Martin <Dave.Martin@arm.com>,
x86-patch-review@intel.com
Subject: Re: [RFC PATCH v9 17/27] x86/cet/shstk: User-mode Shadow Stack support
Date: Tue, 25 Feb 2020 13:07:44 -0800 [thread overview]
Message-ID: <202002251306.2011C9374@keescook> (raw)
In-Reply-To: <20200205181935.3712-18-yu-cheng.yu@intel.com>
On Wed, Feb 05, 2020 at 10:19:25AM -0800, Yu-cheng Yu wrote:
> This patch adds basic Shadow Stack (SHSTK) enabling/disabling routines.
> A task's SHSTK is allocated from memory with VM_SHSTK flag and read-only
> protection. It has a fixed size of RLIMIT_STACK.
>
> v9:
> - Change cpu_feature_enabled() to static_cpu_has().
> - Merge cet_disable_shstk to cet_disable_free_shstk.
> - Remove the empty slot at the top of the SHSTK, as it is not needed.
> - Move do_mmap_locked() to alloc_shstk(), which is a static function.
>
> v6:
> - Create a function do_mmap_locked() for SHSTK allocation.
>
> v2:
> - Change noshstk to no_cet_shstk.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> ---
> arch/x86/include/asm/cet.h | 31 +++++
> arch/x86/include/asm/disabled-features.h | 8 +-
> arch/x86/include/asm/processor.h | 5 +
> arch/x86/kernel/Makefile | 2 +
> arch/x86/kernel/cet.c | 121 ++++++++++++++++++
> arch/x86/kernel/cpu/common.c | 25 ++++
> arch/x86/kernel/process.c | 1 +
> .../arch/x86/include/asm/disabled-features.h | 8 +-
> 8 files changed, 199 insertions(+), 2 deletions(-)
> create mode 100644 arch/x86/include/asm/cet.h
> create mode 100644 arch/x86/kernel/cet.c
>
> diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
> new file mode 100644
> index 000000000000..c44c991ca91f
> --- /dev/null
> +++ b/arch/x86/include/asm/cet.h
> @@ -0,0 +1,31 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_X86_CET_H
> +#define _ASM_X86_CET_H
> +
> +#ifndef __ASSEMBLY__
> +#include <linux/types.h>
> +
> +struct task_struct;
> +/*
> + * Per-thread CET status
> + */
> +struct cet_status {
> + unsigned long shstk_base;
> + unsigned long shstk_size;
> + unsigned int shstk_enabled:1;
> +};
> +
> +#ifdef CONFIG_X86_INTEL_CET
> +int cet_setup_shstk(void);
> +void cet_disable_free_shstk(struct task_struct *p);
> +#else
> +static inline void cet_disable_free_shstk(struct task_struct *p) {}
> +#endif
> +
> +#define cpu_x86_cet_enabled() \
> + (static_cpu_has(X86_FEATURE_SHSTK) || \
> + static_cpu_has(X86_FEATURE_IBT))
> +
> +#endif /* __ASSEMBLY__ */
> +
> +#endif /* _ASM_X86_CET_H */
> diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index 8e1d0bb46361..e1454509ad83 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -62,6 +62,12 @@
> # define DISABLE_PTI (1 << (X86_FEATURE_PTI & 31))
> #endif
>
> +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
> +#define DISABLE_SHSTK 0
> +#else
> +#define DISABLE_SHSTK (1<<(X86_FEATURE_SHSTK & 31))
> +#endif
> +
> /*
> * Make sure to add features to the correct mask
> */
> @@ -81,7 +87,7 @@
> #define DISABLED_MASK13 0
> #define DISABLED_MASK14 0
> #define DISABLED_MASK15 0
> -#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP)
> +#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP|DISABLE_SHSTK)
> #define DISABLED_MASK17 0
> #define DISABLED_MASK18 0
> #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 0340aad3f2fc..793d210e64da 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -25,6 +25,7 @@ struct vm86;
> #include <asm/special_insns.h>
> #include <asm/fpu/types.h>
> #include <asm/unwind_hints.h>
> +#include <asm/cet.h>
>
> #include <linux/personality.h>
> #include <linux/cache.h>
> @@ -539,6 +540,10 @@ struct thread_struct {
> unsigned int sig_on_uaccess_err:1;
> unsigned int uaccess_err:1; /* uaccess failed */
>
> +#ifdef CONFIG_X86_INTEL_CET
> + struct cet_status cet;
> +#endif
> +
> /* Floating point and extended processor state */
> struct fpu fpu;
> /*
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 6175e370ee4a..b8c1ea4ab7eb 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -142,6 +142,8 @@ obj-$(CONFIG_UNWINDER_ORC) += unwind_orc.o
> obj-$(CONFIG_UNWINDER_FRAME_POINTER) += unwind_frame.o
> obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o
>
> +obj-$(CONFIG_X86_INTEL_CET) += cet.o
> +
> ###
> # 64 bit specific files
> ifeq ($(CONFIG_X86_64),y)
> diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
> new file mode 100644
> index 000000000000..b4c7d88e9a8f
> --- /dev/null
> +++ b/arch/x86/kernel/cet.c
> @@ -0,0 +1,121 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * cet.c - Control-flow Enforcement (CET)
> + *
> + * Copyright (c) 2019, Intel Corporation.
> + * Yu-cheng Yu <yu-cheng.yu@intel.com>
> + */
> +
> +#include <linux/types.h>
> +#include <linux/mm.h>
> +#include <linux/mman.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +#include <linux/sched/signal.h>
> +#include <linux/compat.h>
> +#include <asm/msr.h>
> +#include <asm/user.h>
> +#include <asm/fpu/internal.h>
> +#include <asm/fpu/xstate.h>
> +#include <asm/fpu/types.h>
> +#include <asm/cet.h>
> +
> +static void start_update_msrs(void)
> +{
> + fpregs_lock();
> + if (test_thread_flag(TIF_NEED_FPU_LOAD))
> + __fpregs_load_activate();
> +}
> +
> +static void end_update_msrs(void)
> +{
> + fpregs_unlock();
> +}
> +
> +static unsigned long cet_get_shstk_addr(void)
> +{
> + struct fpu *fpu = ¤t->thread.fpu;
> + unsigned long ssp = 0;
> +
> + fpregs_lock();
> +
> + if (fpregs_state_valid(fpu, smp_processor_id())) {
> + rdmsrl(MSR_IA32_PL3_SSP, ssp);
> + } else {
> + struct cet_user_state *p;
> +
> + p = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER);
> + if (p)
> + ssp = p->user_ssp;
> + }
> +
> + fpregs_unlock();
> + return ssp;
> +}
> +
> +static unsigned long alloc_shstk(unsigned long size)
> +{
> + struct mm_struct *mm = current->mm;
> + unsigned long addr, populate;
> +
> + down_write(&mm->mmap_sem);
> + addr = do_mmap(NULL, 0, size, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE,
> + VM_SHSTK, 0, &populate, NULL);
> + up_write(&mm->mmap_sem);
> +
> + if (populate)
> + mm_populate(addr, populate);
> +
> + return addr;
> +}
> +
> +int cet_setup_shstk(void)
> +{
> + unsigned long addr, size;
> + struct cet_status *cet = ¤t->thread.cet;
> +
> + if (!static_cpu_has(X86_FEATURE_SHSTK))
> + return -EOPNOTSUPP;
> +
> + size = rlimit(RLIMIT_STACK);
> + addr = alloc_shstk(size);
> +
> + if (IS_ERR((void *)addr))
> + return PTR_ERR((void *)addr);
> +
> + cet->shstk_base = addr;
> + cet->shstk_size = size;
> + cet->shstk_enabled = 1;
> +
> + start_update_msrs();
> + wrmsrl(MSR_IA32_PL3_SSP, addr + size);
> + wrmsrl(MSR_IA32_U_CET, MSR_IA32_CET_SHSTK_EN);
> + end_update_msrs();
> + return 0;
> +}
> +
> +void cet_disable_free_shstk(struct task_struct *tsk)
> +{
> + struct cet_status *cet = &tsk->thread.cet;
> +
> + if (!static_cpu_has(X86_FEATURE_SHSTK) ||
> + !cet->shstk_enabled || !cet->shstk_base)
> + return;
> +
> + if (!tsk->mm || (tsk->mm != current->mm))
> + return;
> +
> + if (tsk == current) {
> + u64 msr_val;
> +
> + start_update_msrs();
> + rdmsrl(MSR_IA32_U_CET, msr_val);
> + wrmsrl(MSR_IA32_U_CET, msr_val & ~MSR_IA32_CET_SHSTK_EN);
> + end_update_msrs();
> + }
> +
> + vm_munmap(cet->shstk_base, cet->shstk_size);
> + cet->shstk_base = 0;
> + cet->shstk_size = 0;
> + cet->shstk_enabled = 0;
> +}
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 2e4d90294fe6..40498ec72fda 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -54,6 +54,7 @@
> #include <asm/microcode_intel.h>
> #include <asm/intel-family.h>
> #include <asm/cpu_device_id.h>
> +#include <asm/cet.h>
> #include <asm/uv/uv.h>
>
> #include "cpu.h"
> @@ -486,6 +487,29 @@ static __init int setup_disable_pku(char *arg)
> __setup("nopku", setup_disable_pku);
> #endif /* CONFIG_X86_64 */
>
> +static __always_inline void setup_cet(struct cpuinfo_x86 *c)
> +{
> + if (cpu_x86_cet_enabled())
> + cr4_set_bits(X86_CR4_CET);
> +}
> +
> +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
> +static __init int setup_disable_shstk(char *s)
> +{
> + /* require an exact match without trailing characters */
> + if (s[0] != '\0')
> + return 0;
> +
> + if (!boot_cpu_has(X86_FEATURE_SHSTK))
> + return 1;
> +
> + setup_clear_cpu_cap(X86_FEATURE_SHSTK);
> + pr_info("x86: 'no_cet_shstk' specified, disabling Shadow Stack\n");
> + return 1;
> +}
> +__setup("no_cet_shstk", setup_disable_shstk);
> +#endif
I wonder if this should be "cet_shstk=..." instead? Will it always be a
giant knob like this? Will we want to disable it for userspace but keep
it for kernel space, etc?
> +
> /*
> * Some CPU features depend on higher CPUID levels, which may not always
> * be available due to CPUID level capping or broken virtualization
> @@ -1510,6 +1534,7 @@ static void identify_cpu(struct cpuinfo_x86 *c)
> x86_init_rdrand(c);
> x86_init_cache_qos(c);
> setup_pku(c);
> + setup_cet(c);
>
> /*
> * Clear/Set all flags overridden by options, need do it
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 8d0b9442202e..e102e63de641 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -43,6 +43,7 @@
> #include <asm/spec-ctrl.h>
> #include <asm/io_bitmap.h>
> #include <asm/proto.h>
> +#include <asm/cet.h>
>
> #include "process.h"
>
> diff --git a/tools/arch/x86/include/asm/disabled-features.h b/tools/arch/x86/include/asm/disabled-features.h
> index 8e1d0bb46361..e1454509ad83 100644
> --- a/tools/arch/x86/include/asm/disabled-features.h
> +++ b/tools/arch/x86/include/asm/disabled-features.h
> @@ -62,6 +62,12 @@
> # define DISABLE_PTI (1 << (X86_FEATURE_PTI & 31))
> #endif
>
> +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
> +#define DISABLE_SHSTK 0
> +#else
> +#define DISABLE_SHSTK (1<<(X86_FEATURE_SHSTK & 31))
> +#endif
> +
> /*
> * Make sure to add features to the correct mask
> */
> @@ -81,7 +87,7 @@
> #define DISABLED_MASK13 0
> #define DISABLED_MASK14 0
> #define DISABLED_MASK15 0
> -#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP)
> +#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP|DISABLE_SHSTK)
> #define DISABLED_MASK17 0
> #define DISABLED_MASK18 0
> #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
> --
> 2.21.0
>
>
Otherwise, looks good to me. :)
--
Kees Cook
next prev parent reply other threads:[~2020-02-25 21:07 UTC|newest]
Thread overview: 107+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 18:19 [RFC PATCH v9 00/27] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 01/27] Documentation/x86: Add CET description Yu-cheng Yu
2020-02-06 0:16 ` Randy Dunlap
2020-02-06 20:17 ` Yu-cheng Yu
2020-02-25 20:02 ` Kees Cook
2020-02-28 15:55 ` Yu-cheng Yu
2020-02-26 17:57 ` Dave Hansen
2020-03-09 17:00 ` Yu-cheng Yu
2020-03-09 17:21 ` Dave Hansen
2020-03-09 19:27 ` Yu-cheng Yu
2020-03-09 19:35 ` Dave Hansen
2020-03-09 19:50 ` H.J. Lu
2020-03-09 20:16 ` Andy Lutomirski
2020-03-09 20:54 ` H.J. Lu
2020-03-09 20:59 ` Dave Hansen
2020-03-09 21:12 ` H.J. Lu
2020-03-09 22:02 ` Andy Lutomirski
2020-03-09 22:19 ` Dave Hansen
2020-03-09 23:11 ` H.J. Lu
2020-03-09 23:20 ` Dave Hansen
2020-03-09 23:51 ` H.J. Lu
2020-03-09 23:59 ` Andy Lutomirski
2020-03-10 0:08 ` H.J. Lu
2020-03-10 1:21 ` Andy Lutomirski
2020-03-10 2:13 ` H.J. Lu
2020-02-05 18:19 ` [RFC PATCH v9 02/27] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-02-25 20:02 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 03/27] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-02-25 20:04 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 04/27] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-02-25 20:06 ` Kees Cook
2020-02-26 17:10 ` Dave Hansen
2020-03-05 20:44 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection Yu-cheng Yu
2020-02-25 20:07 ` Kees Cook
2020-02-26 17:03 ` Dave Hansen
2020-02-26 19:57 ` Pavel Machek
2020-03-05 20:38 ` Yu-cheng Yu
2020-02-26 18:05 ` Dave Hansen
2020-02-27 1:02 ` H.J. Lu
2020-02-27 1:16 ` Dave Hansen
2020-02-27 2:11 ` H.J. Lu
2020-02-27 3:57 ` Andy Lutomirski
2020-02-27 18:03 ` Dave Hansen
2020-03-06 18:37 ` Yu-cheng Yu
2020-03-06 19:02 ` Dave Hansen
2020-03-06 21:16 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 06/27] mm: Introduce VM_SHSTK for Shadow Stack memory Yu-cheng Yu
2020-02-25 20:07 ` Kees Cook
2020-02-26 18:07 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 07/27] Add guard pages around a Shadow Stack Yu-cheng Yu
2020-02-25 20:11 ` Kees Cook
2020-02-26 18:17 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 08/27] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-02-25 20:12 ` Kees Cook
2020-02-26 18:20 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 09/27] x86/mm: Introduce _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:12 ` Kees Cook
2020-02-26 21:35 ` Dave Hansen
2020-04-01 19:08 ` Yu-cheng Yu
2020-04-01 19:22 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 10/27] x86/mm: Update pte_modify, pmd_modify, and _PAGE_CHG_MASK for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-26 22:02 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 11/27] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-02-25 20:13 ` Kees Cook
2020-02-26 22:04 ` Dave Hansen
2020-04-03 15:42 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 12/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:14 ` Kees Cook
2020-02-26 22:20 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 13/27] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-02-25 20:16 ` Kees Cook
2020-02-26 22:47 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 14/27] mm: Handle Shadow Stack page fault Yu-cheng Yu
2020-02-25 20:20 ` Kees Cook
2020-03-05 18:30 ` Yu-cheng Yu
2020-02-27 0:08 ` Dave Hansen
2020-04-07 18:14 ` Yu-cheng Yu
2020-04-07 22:21 ` Dave Hansen
2020-04-08 18:18 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 15/27] mm: Handle THP/HugeTLB " Yu-cheng Yu
2020-02-25 20:59 ` Kees Cook
2020-03-13 22:00 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 16/27] mm: Update can_follow_write_pte() for Shadow Stack Yu-cheng Yu
2020-02-27 0:34 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 17/27] x86/cet/shstk: User-mode Shadow Stack support Yu-cheng Yu
2020-02-25 21:07 ` Kees Cook [this message]
2020-02-27 0:55 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 18/27] x86/cet/shstk: Introduce WRUSS instruction Yu-cheng Yu
2020-02-25 21:10 ` Kees Cook
2020-03-05 18:39 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 19/27] x86/cet/shstk: Handle signals for Shadow Stack Yu-cheng Yu
2020-02-25 21:17 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 20/27] ELF: UAPI and Kconfig additions for ELF program properties Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 21/27] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND Yu-cheng Yu
2020-02-25 21:18 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 22/27] ELF: Add ELF program property parsing support Yu-cheng Yu
2020-02-25 21:20 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 23/27] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 24/27] x86/cet/shstk: ELF header parsing for Shadow Stack Yu-cheng Yu
2020-02-25 21:22 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 25/27] x86/cet/shstk: Handle thread " Yu-cheng Yu
2020-02-25 21:29 ` Kees Cook
2020-03-25 21:51 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 26/27] mm/mmap: Add Shadow Stack pages to memory accounting Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 27/27] x86/cet/shstk: Add arch_prctl functions for Shadow Stack Yu-cheng Yu
2020-02-25 21:31 ` [RFC PATCH v9 00/27] Control-flow Enforcement: " Kees Cook
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