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 28 void *scs_alloc(int node); 29 void scs_free(void *s); 30 void scs_init(void); 31 int scs_prepare(struct task_struct *tsk, int node); 32 void scs_release(struct task_struct *tsk); 33 scs_task_reset(struct task_struct * tsk)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 __scs_magic(void * s)43static inline unsigned long *__scs_magic(void *s) 44 { 45 return (unsigned long *)(s + SCS_SIZE) - 1; 46 } 47 task_scs_end_corrupted(struct task_struct * tsk)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 56 DECLARE_STATIC_KEY_FALSE(dynamic_scs_enabled); 57 scs_is_dynamic(void)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 scs_is_enabled(void)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 scs_alloc(int node)74static inline void *scs_alloc(int node) { return NULL; } scs_free(void * s)75static inline void scs_free(void *s) {} scs_init(void)76static inline void scs_init(void) {} scs_task_reset(struct task_struct * tsk)77static inline void scs_task_reset(struct task_struct *tsk) {} scs_prepare(struct task_struct * tsk,int node)78static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; } scs_release(struct task_struct * tsk)79static inline void scs_release(struct task_struct *tsk) {} task_scs_end_corrupted(struct task_struct * tsk)80static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; } scs_is_enabled(void)81static inline bool scs_is_enabled(void) { return false; } scs_is_dynamic(void)82static inline bool scs_is_dynamic(void) { return false; } 83 84 #endif /* CONFIG_SHADOW_CALL_STACK */ 85 86 #endif /* _LINUX_SCS_H */ 87