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