1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * Shadow Call Stack support. 4 * 5 * Copyright (C) 2019 Google LLC 6 */ 7 8#ifndef _LINUX_SCS_H 9#define _LINUX_SCS_H 10 11#include <linux/gfp.h> 12#include <linux/poison.h> 13#include <linux/sched.h> 14#include <linux/sizes.h> 15 16#ifdef CONFIG_SHADOW_CALL_STACK 17 18#define SCS_ORDER 0 19#define SCS_SIZE (PAGE_SIZE << SCS_ORDER) 20#define GFP_SCS (GFP_KERNEL | __GFP_ZERO) 21 22/* An illegal pointer value to mark the end of the shadow stack. */ 23#define SCS_END_MAGIC (0x5f6UL + POISON_POINTER_DELTA) 24 25#define task_scs(tsk) (task_thread_info(tsk)->scs_base) 26#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp) 27 28void *scs_alloc(int node); 29void scs_free(void *s); 30void scs_init(void); 31int scs_prepare(struct task_struct *tsk, int node); 32void scs_release(struct task_struct *tsk); 33 34static inline void scs_task_reset(struct task_struct *tsk) 35{ 36 /* 37 * Reset the shadow stack to the base address in case the task 38 * is reused. 39 */ 40 task_scs_sp(tsk) = task_scs(tsk); 41} 42 43static inline unsigned long *__scs_magic(void *s) 44{ 45 return (unsigned long *)(s + SCS_SIZE) - 1; 46} 47 48static inline bool task_scs_end_corrupted(struct task_struct *tsk) 49{ 50 unsigned long *magic = __scs_magic(task_scs(tsk)); 51 unsigned long sz = task_scs_sp(tsk) - task_scs(tsk); 52 53 return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC; 54} 55 56DECLARE_STATIC_KEY_FALSE(dynamic_scs_enabled); 57 58static inline bool scs_is_dynamic(void) 59{ 60 if (!IS_ENABLED(CONFIG_DYNAMIC_SCS)) 61 return false; 62 return static_branch_likely(&dynamic_scs_enabled); 63} 64 65static inline bool scs_is_enabled(void) 66{ 67 if (!IS_ENABLED(CONFIG_DYNAMIC_SCS)) 68 return true; 69 return scs_is_dynamic(); 70} 71 72#else /* CONFIG_SHADOW_CALL_STACK */ 73 74static inline void *scs_alloc(int node) { return NULL; } 75static inline void scs_free(void *s) {} 76static inline void scs_init(void) {} 77static inline void scs_task_reset(struct task_struct *tsk) {} 78static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; } 79static inline void scs_release(struct task_struct *tsk) {} 80static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; } 81static inline bool scs_is_enabled(void) { return false; } 82static inline bool scs_is_dynamic(void) { return false; } 83 84#endif /* CONFIG_SHADOW_CALL_STACK */ 85 86#endif /* _LINUX_SCS_H */ 87