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 /* 19 * In testing, 1 KiB shadow stack size (i.e. 128 stack frames on a 64-bit 20 * architecture) provided ~40% safety margin on stack usage while keeping 21 * memory allocation overhead reasonable. 22 */ 23 #define SCS_SIZE SZ_1K 24 #define GFP_SCS (GFP_KERNEL | __GFP_ZERO) 25 26 /* An illegal pointer value to mark the end of the shadow stack. */ 27 #define SCS_END_MAGIC (0x5f6UL + POISON_POINTER_DELTA) 28 29 #define task_scs(tsk) (task_thread_info(tsk)->scs_base) 30 #define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp) 31 32 void scs_init(void); 33 int scs_prepare(struct task_struct *tsk, int node); 34 void scs_release(struct task_struct *tsk); 35 36 static inline void scs_task_reset(struct task_struct *tsk) 37 { 38 /* 39 * Reset the shadow stack to the base address in case the task 40 * is reused. 41 */ 42 task_scs_sp(tsk) = task_scs(tsk); 43 } 44 45 static inline unsigned long *__scs_magic(void *s) 46 { 47 return (unsigned long *)(s + SCS_SIZE) - 1; 48 } 49 50 static inline bool scs_corrupted(struct task_struct *tsk) 51 { 52 unsigned long *magic = __scs_magic(task_scs(tsk)); 53 unsigned long sz = task_scs_sp(tsk) - task_scs(tsk); 54 55 return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC; 56 } 57 58 #else /* CONFIG_SHADOW_CALL_STACK */ 59 60 static inline void scs_init(void) {} 61 static inline void scs_task_reset(struct task_struct *tsk) {} 62 static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; } 63 static inline bool scs_corrupted(struct task_struct *tsk) { return false; } 64 static inline void scs_release(struct task_struct *tsk) {} 65 66 #endif /* CONFIG_SHADOW_CALL_STACK */ 67 68 #endif /* _LINUX_SCS_H */ 69