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9beccca098
In order to allow arches to use code patching to conditionally emit the shadow stack pushes and pops, rather than always taking the performance hit even on CPUs that implement alternatives such as stack pointer authentication on arm64, add a Kconfig symbol that can be set by the arch to omit the SCS codegen itself, without otherwise affecting how support code for SCS and compiler options (for register reservation, for instance) are emitted. Also, add a static key and some plumbing to omit the allocation of shadow call stack for dynamic SCS configurations if SCS is disabled at runtime. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Tested-by: Sami Tolvanen <samitolvanen@google.com> Link: https://lore.kernel.org/r/20221027155908.1940624-3-ardb@kernel.org Signed-off-by: Will Deacon <will@kernel.org>
86 lines
2.3 KiB
C
86 lines
2.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Shadow Call Stack support.
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*
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* Copyright (C) 2019 Google LLC
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*/
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#ifndef _LINUX_SCS_H
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#define _LINUX_SCS_H
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#include <linux/gfp.h>
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#include <linux/poison.h>
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#include <linux/sched.h>
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#include <linux/sizes.h>
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#ifdef CONFIG_SHADOW_CALL_STACK
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#define SCS_ORDER 0
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#define SCS_SIZE (PAGE_SIZE << SCS_ORDER)
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#define GFP_SCS (GFP_KERNEL | __GFP_ZERO)
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/* An illegal pointer value to mark the end of the shadow stack. */
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#define SCS_END_MAGIC (0x5f6UL + POISON_POINTER_DELTA)
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#define task_scs(tsk) (task_thread_info(tsk)->scs_base)
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#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp)
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void *scs_alloc(int node);
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void scs_free(void *s);
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void scs_init(void);
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int scs_prepare(struct task_struct *tsk, int node);
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void scs_release(struct task_struct *tsk);
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static inline void scs_task_reset(struct task_struct *tsk)
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{
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/*
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* Reset the shadow stack to the base address in case the task
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* is reused.
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*/
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task_scs_sp(tsk) = task_scs(tsk);
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}
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static inline unsigned long *__scs_magic(void *s)
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{
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return (unsigned long *)(s + SCS_SIZE) - 1;
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}
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static inline bool task_scs_end_corrupted(struct task_struct *tsk)
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{
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unsigned long *magic = __scs_magic(task_scs(tsk));
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unsigned long sz = task_scs_sp(tsk) - task_scs(tsk);
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return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC;
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}
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DECLARE_STATIC_KEY_FALSE(dynamic_scs_enabled);
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static inline bool scs_is_dynamic(void)
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{
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if (!IS_ENABLED(CONFIG_DYNAMIC_SCS))
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return false;
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return static_branch_likely(&dynamic_scs_enabled);
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}
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static inline bool scs_is_enabled(void)
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{
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if (!IS_ENABLED(CONFIG_DYNAMIC_SCS))
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return true;
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return scs_is_dynamic();
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}
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#else /* CONFIG_SHADOW_CALL_STACK */
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static inline void *scs_alloc(int node) { return NULL; }
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static inline void scs_free(void *s) {}
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static inline void scs_init(void) {}
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static inline void scs_task_reset(struct task_struct *tsk) {}
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static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
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static inline void scs_release(struct task_struct *tsk) {}
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static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
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static inline bool scs_is_enabled(void) { return false; }
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static inline bool scs_is_dynamic(void) { return false; }
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#endif /* CONFIG_SHADOW_CALL_STACK */
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#endif /* _LINUX_SCS_H */
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