1  /* SPDX-License-Identifier: GPL-2.0 */
2  #ifndef _LINUX_STACKLEAK_H
3  #define _LINUX_STACKLEAK_H
4  
5  #include <linux/sched.h>
6  #include <linux/sched/task_stack.h>
7  
8  /*
9   * Check that the poison value points to the unused hole in the
10   * virtual memory map for your platform.
11   */
12  #define STACKLEAK_POISON -0xBEEF
13  #define STACKLEAK_SEARCH_DEPTH 128
14  
15  #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
16  #include <asm/stacktrace.h>
17  #include <linux/linkage.h>
18  
19  /*
20   * The lowest address on tsk's stack which we can plausibly erase.
21   */
22  static __always_inline unsigned long
stackleak_task_low_bound(const struct task_struct * tsk)23  stackleak_task_low_bound(const struct task_struct *tsk)
24  {
25  	/*
26  	 * The lowest unsigned long on the task stack contains STACK_END_MAGIC,
27  	 * which we must not corrupt.
28  	 */
29  	return (unsigned long)end_of_stack(tsk) + sizeof(unsigned long);
30  }
31  
32  /*
33   * The address immediately after the highest address on tsk's stack which we
34   * can plausibly erase.
35   */
36  static __always_inline unsigned long
stackleak_task_high_bound(const struct task_struct * tsk)37  stackleak_task_high_bound(const struct task_struct *tsk)
38  {
39  	/*
40  	 * The task's pt_regs lives at the top of the task stack and will be
41  	 * overwritten by exception entry, so there's no need to erase them.
42  	 */
43  	return (unsigned long)task_pt_regs(tsk);
44  }
45  
46  /*
47   * Find the address immediately above the poisoned region of the stack, where
48   * that region falls between 'low' (inclusive) and 'high' (exclusive).
49   */
50  static __always_inline unsigned long
stackleak_find_top_of_poison(const unsigned long low,const unsigned long high)51  stackleak_find_top_of_poison(const unsigned long low, const unsigned long high)
52  {
53  	const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
54  	unsigned int poison_count = 0;
55  	unsigned long poison_high = high;
56  	unsigned long sp = high;
57  
58  	while (sp > low && poison_count < depth) {
59  		sp -= sizeof(unsigned long);
60  
61  		if (*(unsigned long *)sp == STACKLEAK_POISON) {
62  			poison_count++;
63  		} else {
64  			poison_count = 0;
65  			poison_high = sp;
66  		}
67  	}
68  
69  	return poison_high;
70  }
71  
stackleak_task_init(struct task_struct * t)72  static inline void stackleak_task_init(struct task_struct *t)
73  {
74  	t->lowest_stack = stackleak_task_low_bound(t);
75  # ifdef CONFIG_STACKLEAK_METRICS
76  	t->prev_lowest_stack = t->lowest_stack;
77  # endif
78  }
79  
80  asmlinkage void noinstr stackleak_erase(void);
81  asmlinkage void noinstr stackleak_erase_on_task_stack(void);
82  asmlinkage void noinstr stackleak_erase_off_task_stack(void);
83  void __no_caller_saved_registers noinstr stackleak_track_stack(void);
84  
85  #else /* !CONFIG_GCC_PLUGIN_STACKLEAK */
stackleak_task_init(struct task_struct * t)86  static inline void stackleak_task_init(struct task_struct *t) { }
87  #endif
88  
89  #endif
90