/* 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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#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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#endif /* CONFIG_SHADOW_CALL_STACK */
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#endif /* _LINUX_SCS_H */
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