include/linux/scs.h

   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
  34 static 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
  43 static inline unsigned long *__scs_magic(void *s)
  44 {
  45         return (unsigned long *)(s + SCS_SIZE) - 1;
  46 }
  47
  48 static 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 #else /* CONFIG_SHADOW_CALL_STACK */
  57
  58 static inline void *scs_alloc(int node) { return NULL; }
  59 static inline void scs_free(void *s) {}
  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 void scs_release(struct task_struct *tsk) {}
  64 static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
  65
  66 #endif /* CONFIG_SHADOW_CALL_STACK */
  67
  68 #endif /* _LINUX_SCS_H */