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 
18 /*
19  * The lowest address on tsk's stack which we can plausibly erase.
20  */
21 static __always_inline unsigned long
stackleak_task_low_bound(const struct task_struct * tsk)22 stackleak_task_low_bound(const struct task_struct *tsk)
23 {
24 	/*
25 	 * The lowest unsigned long on the task stack contains STACK_END_MAGIC,
26 	 * which we must not corrupt.
27 	 */
28 	return (unsigned long)end_of_stack(tsk) + sizeof(unsigned long);
29 }
30 
31 /*
32  * The address immediately after the highest address on tsk's stack which we
33  * can plausibly erase.
34  */
35 static __always_inline unsigned long
stackleak_task_high_bound(const struct task_struct * tsk)36 stackleak_task_high_bound(const struct task_struct *tsk)
37 {
38 	/*
39 	 * The task's pt_regs lives at the top of the task stack and will be
40 	 * overwritten by exception entry, so there's no need to erase them.
41 	 */
42 	return (unsigned long)task_pt_regs(tsk);
43 }
44 
45 /*
46  * Find the address immediately above the poisoned region of the stack, where
47  * that region falls between 'low' (inclusive) and 'high' (exclusive).
48  */
49 static __always_inline unsigned long
stackleak_find_top_of_poison(const unsigned long low,const unsigned long high)50 stackleak_find_top_of_poison(const unsigned long low, const unsigned long high)
51 {
52 	const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
53 	unsigned int poison_count = 0;
54 	unsigned long poison_high = high;
55 	unsigned long sp = high;
56 
57 	while (sp > low && poison_count < depth) {
58 		sp -= sizeof(unsigned long);
59 
60 		if (*(unsigned long *)sp == STACKLEAK_POISON) {
61 			poison_count++;
62 		} else {
63 			poison_count = 0;
64 			poison_high = sp;
65 		}
66 	}
67 
68 	return poison_high;
69 }
70 
stackleak_task_init(struct task_struct * t)71 static inline void stackleak_task_init(struct task_struct *t)
72 {
73 	t->lowest_stack = stackleak_task_low_bound(t);
74 # ifdef CONFIG_STACKLEAK_METRICS
75 	t->prev_lowest_stack = t->lowest_stack;
76 # endif
77 }
78 
79 #else /* !CONFIG_GCC_PLUGIN_STACKLEAK */
stackleak_task_init(struct task_struct * t)80 static inline void stackleak_task_init(struct task_struct *t) { }
81 #endif
82 
83 #endif
84